FalcorJS with AngularJS v1.x

Ever since it was presented at ng-conf, I've been excited to get my hands on Netflix's new "One Model Everywhere" data-fetching framework: FalcorJS.  Now it's been released on the world as a Developer Preview, I wanted to show how it can be used with AngularJS v1.x.

What is FalcorJS?

"A JavaScript library for efficient data fetching"

That sums up FalcorJS pretty well.
It's designed to retrieve only as much data as you need at a time by letting the view specify the values it needs, then the model can batch those requests up when it calls the server.

Falcor represents your data as a big JSON 'graph', which means you can request the same data from different paths and it will use the cache from the first request.

Sample from FalcorJS' JSON Graph Guide

One odd thing you will have to get used to with FalcorJS is that you only request 1 value at a time. And by "value" I mean: string, number, boolean, or null. This feels totally alien coming from... everything else, but it works because FalcorJS takes care of the efficiencies for you. Instead of having 1 request for an array of objects, which you then have to split up into 20 fields on your view - you instead make 20 requests from your view, which are automatically batched for you into 1 request.

Other mechanics that Falcor provides is functions on your JSON Graph than you can 'call()', which is good for things like creating whole new objects and transactions where you want to be sure everything is being handled in one go. Responses can also include multiple values, for situations where you're sure it's going to be required, and can specify what routes should have their cache invalidated.

The last thing to mention is that FalcorJS is built on Observables from RxJS for all it's asynchronous operations. For those unfamiliar with them, Observables and the whole ReactiveX API are the ultimate asynchronous toolkit. Observables fill in the gaps with Promises, things like how to handle multiple values over time, and whether new 'observers' see just new values or the preceding values too. I won't go into Observables too much, but there are lots and lots of excellent resources online.

Using with AngularJS v1.x

Disclaimer: Once again, FalcorJS is in Developer Preview. So what's written here today may not work tomorrow. Check the FalcorJS API Reference and Github if you have difficulties.

In this example we're going to build a UI with AngularJS v1.x that uses a FalcorJS Model with a HttpDataSource pointed at our falcor-express-demo and falcor-router-demo server.

With our Model setup we can pull values from the server using this.model.getValue(path). It will then build the necessary XHR call and return an Observable for it's result.

The $apply problem

Wait a sec... if it makes it's own XHR call, how will Angular know when to start a $digest loop?

Well the usual solution in these circumstances is to use $scope.$apply(), such as when binding to an event that's not triggered within Angular's digest loop. However we can't actually be 100% sure that we're not in the digest loop either. For example, if we're hitting cached values, all the callback functions could be called immediately. A better solution is to use $scope.$evalAsync() which will start a new digest loop if, and only if, one is not already in progress. So any time we subscribe to an Observable, we simply need to call $scope.$evalAsync() and we're good to go.

Calling from the View

The next thing we want is to start making calls from the View rather than making it the controller's responsibility. This helps to decouple the view and the controller further (all the controller supplies is a reference to the model), and means we're only requesting as much data as we're actually using. eg. If we're showing a cut-down mobile friendly view, we don't have to pull back as much data.
But how are we going to get our results onto the View? All our requests are going to return fresh Observables.

This is where the Model.getCache(path) method comes in. It synchronously returns the value from the Model's cache. If that returns undefined, we can call Model.getValue(path).subscribe(_ => $scope.$evalAsync()) - It'll request the value and call $scope.$evalAsync() once it returns, which means a new digest loop, which will trigger a new call, which will get a successful hit from the cache.

Dealing with collections

Since FalcorJS doesn't support returning objects and arrays (well, sort of) we need a way to deal with collections in our data. The solution that I prefer is to generate an array of index numbers which represent a 'page range', and request the length of your collection ahead of time to set your max index.

Another thing you may be able to use is the Model.deref(path) method, passing the result to another directive that can handle resolving the Observable.

What about writing data?

Falcor comes with two primary methods for writing values: setValue(path, value) and call(path, args).

setValue() sets the value for a particular path, returning an Observable for the result. Integrating it with ng-model is simple using ng-model-options="{getterSetter: true}". We create a function which takes the model and the path, then returns a function which either calls getValue() or setValue(), depending on the number of arguments.

setValue() is great if you want to set one value at a time. But what if you want to save the entire form at once, after you've confirmed your data is valid?
This is where call() comes in.

The Falcor Router supports 3 different types of operations on each route: get, set, and call. call turns the route into an RPC endpoint where you pass in arguments, which can include objects and arrays (anything that can be JSON encoded), and it returns a set of PathValues and cache invalidations for the Falcor Model to interpret.

Summary

Once again I have to repeat: Falcor is in "Developer Preview" mode. Which means that not only is it not ready for production, but it's also only recommended for those of us who like to cut ourselves on the bleeding edge.

With that in mind: Falcor is pretty solid, and the learning curve is quite smooth. It does require rethinking your data API to fit "the falcor way", but that's a common cost with opinionated frameworks which pays back with simpler and more consistent code.

Where it really excels most is with "mostly-read/rarely-write" type applications, but you can still do write operations with `setValue()` and `calls()`. I probably wouldn't try to write any games with it (though that might be a fun exercise all the same).

I've started a github repository with a working example of everything I've shown here, along with a "falcor" module that encapsulates the falcor specific code.

Cheers,
Jason Stone

Tips for designing a JSON Schema

I've been writing a lot of JSON schemas lately.
Some were just small API requests and responses.
Some were big all encompassing documents that involves over 20 unique object types.

When I started the big ones, I went looking around the internet for some resources.  What I found was plenty on how to write a JSON Schema (This being the best one), but not on how to design one.
To contrast, there's plenty of material available on how to design relational database schemas - from blog articles to university subjects.
I still managed to come up with something resembling a process, so I thought I'd share with the class in the hopes it'll help someone else.

Just a quick disclaimer: These are just my own personal findings and opinions.
If you have your own findings that you think are better, by all means stick to them.  Share them with the class too, if you can.

Read the 'JSON API' standard

I cannot emphasise this point enough.
Go to http://jsonapi.org/ and read through the documentation and examples.
I'm not expecting you to implement it - especially if you're not creating JSON Schemas for a web API - but it's great example of a JSON based standard, and well worth the time to look at.  I've based a lot of my own schemas off elements of it, without implementing it completely.
Things like using the "id", "type", and "links" keywords.

If you do decide to implement it, take into account that it's a work in progress.
In the last month they've published a release candidate which had some significant differences from the previously published versions. But the fact that they're calling it a "release candidate" says it should be pretty stable by now.

Keep a flat structure

Don't embed objects within objects within objects within objects.
You're better off keeping a flat structure of one or many arrays at the top level containing objects.
Rather than nesting one object inside another, create a separate object in one of those arrays and link the two together - even if you're sure it's a 1-to-1 relationship for both objects.
The JSON API uses a single "included" array that contains all additional objects.  I personally prefer having multiple arrays that group the objects by "type" - but that's me.

You can also use the same prefix for property names, rather than creating a new embedded object.
eg. {"name": {"first": "John", "last": "Smith"}} becomes {"nameFirst": "John", "nameLast": "Smith"}

Why?

• It means less code like this:
  var value = data.article && data.article.author && data.article.author.phone && data.article.author.phone.number;
• It simplifies things if you're marshalling and unmarshalling your JSON into and out of other data structure. eg. Classes and SQL tables.
  Even if you're using a NoSQL DB with NodeJS today - tomorrow you might create a new microservice in something new. Doesn't hurt to be flexible.
• You have a 1-to-1 link today, but a new feature tomorrow might change that.
  Keeping things flat give you some extra flexibility for the future.

Work out how relationships are defined

Even if you don't go with a flat structure, you're going to need some way to say "X relates to Y because Z" - unless you honestly plan to duplicate and embed each and every object.
Take a look at how JSON API does it - the way the "links" property contains relationships, and each of those has a "linkage" object(s) with the "id" and "type" of the other object(s).
You don't need to do the exact same thing. But you should be consistent throughout your entire schema.
Preferably throughout all the schemas in your organisation, if you can manage it.

Why?

Because if you have a consistent format for defining relationship, you can write functions that will traverse those relationships for you.

New properties are cheap

Sometimes there's the temptation to reuse the same property for a slightly different purpose.
Maybe you want to define an "accountType" which then gives a completely different context to the 5 other properties, and you think "I just saved myself from writing 5 new properties into the schema, for the price of 1 - woooo!"

Don't do that.

Of all the possible schema changes you could make - new properties are the cheapest.
Don't make things more confusing by trying to shove square pegs into round holes.
Unless you are writing super memory efficient software, where you need to squeeze every last bit from the hardware (in which case, why are you using JSON at all?) - just make a new property.

Prepare for change

No matter how hard you try, how long you work, how much you analyse and survey and workshop - there's going to be something you need to change in the structure of the schema.
Now you can either live in constant fear of this day, or you can work out your strategy ahead of time.

Embed the version of the schema in your JSON documents and have a process in place for running migration scripts.
Whether your strategy is a 'big-bang' during downtime or an ongoing background process.
Just have your migration process ready.

Use "allOf" to create schema mixins

I said this wasn't about how to write a JSON Schema, just how to design it - this is the exception.

I gave the example earlier of prefixing property names rather than nesting objects - 'name' to 'firstName' and 'lastName'.
But what if you have 5 different objects that need to have a 'name'?
Am I supposed to duplicate that in the schema 5 times too?

No.

The JSON Schema standard defines a number of keywords that can be used to combine schemas: "oneOf", "allOf", and "anyOf".
"oneOf" is good for applying "switch" logic branching.
"anyOf" is for when you're a lot more forgiving.
"allOf" is great for constructing a schema from sub-schemas.
For example you can create a sub-schema for an object with "nameFirst" and "nameLast" properties, and include it as part of the schema for a completely different object.

Cheers,
Jason Stone

Using ES6 with your AngularJS project

Earlier this month Glen Maddern (aka. The <x-gif> guy) posted an article, Javascript in 2015, with a YouTube video giving "A brief tour of JSPM, SystemJS & ES6 features".
If you haven't seen it already, go take a look.

In a short time he has a front-end application written in ES6 running, with modules being loaded and transpiled (via Traceur) by SystemJS.  And at the end he creates a self-executing, minified bundle of that application code, including source maps.

These tools make it easy to start using ES6 now with your existing AngularJS applications - which will almost certainly be step 1 on the migration plan to Angular v2.0. Even without that, the goodies from ES6 are too good to pass up.

As a demonstration, we're going to take angular-seed, update it to ES6 using SystemJS, bundle the app for production with systemjs-builder, and configure Karma to run unit tests using the karma-systemjs plugin.

SystemJS Setup

OK - lets get started.
We're going to clone an angular-seed repo, switch to a new es6 branch, then install dependencies from npm and bower. The dependencies for angular-seed are a bit old, so we've updated them too:

git clone https://github.com/angular/angular-seed.git
cd angular-seed
git checkout -b es6
npm install --save-dev systemjs-builder karma-systemjs karma#~0.12 karma-chrome-launcher karma-firefox-launcher karma-jasmine
bower install -f -S angular#1.3.x angular-route#1.3.x angular-mocks#~1.3.x system.js

Next thing we need is a config file for SystemJS: `app/system.config.js`. This is where we tell SystemJS how to find certain modules.  In this case, we're going to map the module names 'angular' and 'angular-route' to their long paths:

Next we'll change `app/index-async.html` to use SystemJS rather than angular-loader:

Last thing to do is add `import` statements to `app/app.js` to include the rest of the application, as it's what will be loaded by `System.import('app')`:

Now if you load up `app/index-async.html` using a local webserver (The one included with angular-seed start with `npm start`) you should see the angular-seed application running as normal, only it's been loaded as a set of ES6 files.

This is just the bare minimum required to get existing code to ES6 using SystemJS.
You can add more ES6 syntax and rearrange the modules as you like.

Here's my suggestions:

• Use classes for Controllers (Controller as), Services (.service()), and Providers
• Use ES6 modules over angular modules
• Use arrow functions - cause they're sugary sweet!

Bundling for Production

With our SystemJS config file already in place, we only need to pass that into systemjs-builder with a slight tweak to bundle our code for production. This is a simple node script you can run with `node bundle.js` that will bundle all the modules imported by `app/app.js` and output the result to `app/bundle.js`:

And finally we change `app/index.html` to include `traceur-runtime.js` and the `bundle.js` file we just created:

Unit Testing

Karma works like most a typical browser application: Load all <script/> tags, then start the application `onload`. In this case, we want Karma to let SystemJS handle loading everything, then start the test runner once everything is ready.  This is essentially what karma-systemjs does for us.

First we need to adjust `karma.conf.js`:

Next we update our test suites to act like ES6 modules - importing the code to be tested, along with any dependency libraries.

Note how `module()` has been changed to `angular.mock.module()`.

And that's it.
An existing AngularJS project converted over to using ES6 with SystemJS, with working unit tests and a means of generating bundles for production.
You can find the complete code here: https://github.com/rolaveric/angular-seed/tree/es6

Cheers,
Jason Stone

ng-europe Retrospective Part 2: RIP

In the last post we went through some of the new Javascript syntax that the Angular team are trialling through AtScript, a superset of TypeScript, which is a superset of ES6...

In this post we'll look at what's being removed between v1.x and v2.0 - The victims from Igor Minar and Tobias Bosch's talk at ng-europe.

First, it's worth mentioning some of the great material that's come up since the last post.

• More videos from ng-europe have been uploaded to YouTube: ng-europe channel
• Tero Parviainen talked about why Angular 2 will still be Angular.
• Lukas Ruebbelke gives us 10 Things To Consider While Keeping a Level Head About AngularJS 2.0.
• Misko Hevery opens up discussion about the templating syntax in Angular 2.
• Matt Asay explains Why Web Tools Like AngularJS Need To Keep Breaking Themselves.

And no doubt there'll be more good stuff published in the coming days.  Keep an eye on #AngularJS and the AngularJS team on Twitter and Google+.

Now then.  Lets take a look at the kill list.

RIP

First, a little disclaimer: I don't know for sure what Angular v2.0 will look like.
Nobody does for sure.  Not even the Angular team, because they haven't finished it yet.
I'm merely extrapolating from the ng-europe presentations, and what's currently available in AngularDart.

Controllers

Controllers, as we know them, are going.
This has already been trialled in AngularDart.  Controllers were originally a sub-class of directives, but were eventually deprecated and then removed for the release of v1.0.

Instead you will have a way to expose the properties and methods of a class with a @Directive annotation onto your templates.  Igor and Tobias' talk mentioned some of the potential Directive subclasses that will make things easier for you.

The closest equivalent in v1.x I can think of would be a directive with a 'controller' and a 'controllerAs', like so:

Directive Definition Object (DDO)

The old DDO syntax that we all know and... know, for writing directives will be gone.
The heart of your directive logic will be a class, with annotations that describe how the directive will be used.

Once again, to get the best idea of how this will work, look no further than AngularDart.

$scope

Now this is an interesting one - the classic $scope object gone for good.
How is that even possible?

Well, $scope provides 3 main functions:

• exposing properties to the template
• creating watchers
• and handling events

The first is somewhat redundant because every control-I mean, every component class will be exposing it's public properties to the template.  As though "controllerAs" had become mandatory.

Watchers will be handled by their own new module: watchtower.js
This allows watchers to be grouped together in a way which doesn't depend on... well, anything really. But certainly not a scope hierarchy like in Angular v1.x

As for events... I'm not sure.
I haven't seen anything specific about events, so I can only speculate.
In saying that - my money is on using the native DOM API for events, as that's how Angular v2.0 is heading for DOM manipulation.

Speaking of which...

jqLite

The Angular team have found that jqLite has become too much of a performance bottleneck for them.
And since Angular v2.0 is for evergreen browsers, they have no fear of relying on native implementations of the DOM API.

DOM traversal is easily handled by querySelector() and querySelectorAll(), events with addEventListener(), and good old createElement(), setAttribute(), and appendChild() for manipulation.

But in the end, if you want to use jQuery, there's nothing stopping you from using it.
It just won't be part of the Angular Core.

angular.module

angular.module() has 2 somewhat overlapping jobs:

• Register different types of components (eg. Directives, controllers, filters, etc.)
• and register injectables and their dependencies.

The first has been replaced by annotations, like @Directive.
The second has been split into it's own module: di.js

The workings of di.js is pretty simple.
You declare the dependencies for a class using the @Inject annotation, specifying the class for each dependency (The actual class - not just it's name as a string, like Angular v1.x does), and then create an Injector for the classes you want.
Checkout the example on the di.js github: kitchen-di

The great thing about this is that it doesn't make any assumptions about your application.  It's totally separated from Angular.
You can even create multiple injectors, maybe one for each instance of a directive.

ng-app

This wasn't listed with the other tombstones, but you'll notice it was missing from the slide with the experimental template syntax.
It's also not used by AngularDart applications.
Instead they create their own application object, which you then register classes with, and then run the application.  Not unlike "angular.bootstrap()".
I think Angular v2.0 will do something similar.

Final Thoughts

These changes are about making your code less "Angular" and more "Javascript".
But nothing is really set in stone yet for Angular v2.0:

Reminder that the @angularjs 2.0 announcements are a call for feedback, not a final design. We're listening to your feedback!
— Brian Ford (@briantford) October 31, 2014

In my next post I'm going to make some wild assumptions about Angular v2.0 and come up with some things we can do with our v1.x code to make the transition easier.
(Spoiler alert: It's going to involve ES6)

ng-europe Retrospective Part 1: New Syntax

ng-europe, the European AngularJS conference, was held last week in Paris (France - not that other Paris), and the videos from the sessions were uploaded to Youtube earlier this week:
https://www.youtube.com/channel/UCEGUP3TJJfMsEM_1y8iviSQ

The main topic around the conference was, to no one's surprise, AngularJS v2.0
When will it be released? What will it bring? What will it break?
The answers to which break down to: Soon ™; The same but faster and using future standards; And a lot less than some people are panicking about.

If I were to sum up what I've seen of AngularJS v2.0: It will have everything that AngularDart got, with some of the crust cut off.
In fact, the Angular team have organised the source code so that they can build AngularJS and AngularDart from the same code base, which is an impressive feat.

New Syntax

Wait... but how can they do that?
AngularDart uses classes and type reflection to handle dependency injection, and annotations for marking classes as directives or web components.
These things aren't in Javascript...
But they are in ES6, TypeScript, and AtScript.

Confused?
That's where this slide comes in handy.

Classes

The class syntax is being standardised in ES6.
And when it's compiled down to ES5, it uses the good old Javascript prototype chain: Effective but ugly.

Types

For dependency injection to work we need to know what type of objects each dependency is.  Today this is achieved by identifying dependencies with strings.
For Angular v2.0, the Angular team wants to move away from this idea that everything must be registered explicitly with Angular (ie. module.factory(), module.value(), etc.) and instead just use classes.  Same way it's been done for AngularDart.

The trouble is that ES6 still has no syntax for declaring that a parameter should be a particular type.
If I want my function to only accept parameter "meep" if it came from "MyClass", then I'm going to have to do my own manual "meep instanceof MyClass" check.
This is where the "name:type" syntax comes in.  It provides both type assertions at runtime, and documentation.
It's currently being used by TypeScript, and a proposal was drafted for ES6, but it looks like it will be deferred till ES7 at least.

Type Introspection

What TypeScript does is great for doing type checking on values, but it doesn't actually help with things like dependency injection.  It's not about passing in the correct values to a function - It's about knowing what the function wants in the first place.
That's where the need for type introspection (or type reflection) comes in.

Looking at the code generated by traceur, AtScript's solution is to attach the classes or some equivalent to the function as a property called "parameters".  Simple, but effective.

Annotations

The last piece is annotations.  Metadata which declares something about a class or function without directly interfering with it.
Annotations become a property of the function called "annotations", similar to parameters.

Final Thoughts

All of these new syntaxes are going to be added to Javascript, sooner or later, and I believe they'll be a welcome addition to the language.

Creating class-like structures right now requires either a third-party library or some very ugly looking uses of the 'prototype' property.  It's about time it got standardised.

Fact: Types are useful.
If you don't want to use them, fine.  The type system is optional.

But they can help stop trivial bugs, make IDEs more useful, and refactoring a lot easier.

And I think the way Angular uses annotations proves just how useful they can be.

Next Time

Next time I'm going to take a look through the things Igor and Tobias mentioned will be killed off in Angular v2.0, and what will replace them.
After that I'll take a look at a few things we could do in v1.x that might make migrating to v2.0 a little less jarring.

Till then.

Cheers,

Jason Stone

Guide to Javascript on Classic ASP

Disclaimer: As the title says, this is for Classic ASP with "Javascript".  If your project is using Visual Basic, you may be able to glean some information from this article, but it's not written with you in mind.

I've had some recent experience with a legacy system using Javascript (technically "JScript") on Classic ASP, and the thing I found most frustrating was the lack of coherent documentation available. Despite it's reputation, w3schools is still one of the best references available on the web.

I guess this shouldn't be a surprise.  It is a deprecated platform, and they don't call it "Classic" for nothing. But there are still legacy systems out there which need to be maintained. If the system is purely in maintenance mode, you can probably get along just by reading the existing code and holding your nose. But if you need to add features and make significant changes, it's worth knowing some of Classic ASP's secrets so you can take advantage of the modern Javascript ecosystem.

Note: This is meant to be a reference for anyone who's forced to work with Classic ASP. In no way am I condoning using it by choice.  But if you've got to use it - use it right.

Javascript in Classic ASP is ECMAScript 3

First thing to be aware of is that the code you're writing, at it's core, is ECMAScript 3.  Another way to think of it: If your code runs in IE8 (minus the DOM API, obviously) it'll run in Classic ASP.

I've seen some developers approach Classic ASP code like it's some ancient writing which only the old masters knew how to interpret.  It's not.  There are only 6 things which are not, strictly speaking, Javascript: Request, Response, Server, Application, Session, and ASPError.

Your biggest challenge is learning to live without features from ES5, or finding appropriate shims.

The global scope cannot be directly manipulated

This is the biggest WTF to get your head around if you're used to coding in browsers or NodeJS. Trying to work with the global scope object as "this" will cause errors, giving developers the false impression that modern libraries won't work with Classic ASP.

Say you've got a third party library (like UnderscoreJS) that declares itself like so:

(function () {

  this.myExport = {};

}).call(this);

If I try to run this in Classic ASP, it will throw an error.

You can easily work around it, though it is somewhat tedious:

var surrogate = {};

(function () {

  this.myExport = {};

}).call(surrogate);

var myExport = surrogate.myExport;

Use <script src="" runat="server"> to include code without tags

Most Classic ASP I know uses the #include directive provided by IIS to compose source files.  The directive works by essentially pasting the entire file content into the directive location, like so:

include.asp:

<script runat="server">

var myInclude = {};

</script>

main.asp:

<!-- #include file="include.asp" -->

<script runat="server">

var myProgram = {include: myInclude};

</script>

Results in:

<script runat="server">

var myInclude = {};

</script>

<script runat="server">

var myProgram = {include: myInclude};

</script>

The downside to this is that you can't use any Javascript code quality tools.  They'll start to parse your file, find the tags, and throw syntax errors. This prevents you from doing style checks, code coverage, and code metrics. It can also cause headaches for editors and IDEs.

Instead you can use <script src="" runat="server"> to include files into your tags, just like any ".js" file into HTML:

include.js

var myInclude = {};

main.asp:

<script src="include.js" runat="server"></script>

<script runat="server">

var myProgram = {include: myInclude};

</script>

Using this method, there's noth... very little to stop you using the same tools enjoyed by NodeJS developers. Though you obviously need to be configure IIS so that it doesn't expose your code files as static resources.
That would be bad...

Code in <% %> tags is parsed before <script runat="server"></script> tags

This was a bit of a head scratcher when I first discovered it.  But sure enough, code in <% %> tags executes before <script runat="server"></script> tags (stackoverflow).

<script runat="server">Response.Write("first");</script>

<%Response.Write("second");%>

Result: second, first

My recommendation is: Don't use <% %> tags.

It's too easy to create tag soup, and you're better off using <script src="" runat="server"> anyway for JS code tooling.

Core ASP objects don't produce Javascript primitives

var param = Request.QueryString('param');

param == "test"; // true

param === "test"; // false

String(param) === "test"; true

This means you tried to call "param.substring(1)", it would throw an error saying that "substring" was undefined.  So you need to make sure you wrap results from core ASP objects in String(), Number(), or Boolean() before you try to use them.

That about does it.

To all the poor bastards out there stuck working on Classic ASP: This is for you.

See more on Know Your Meme

E2E testing AngularJS with Protractor

In the beginning, there was JSTestDriver.
It was a dark time, with much wailing and gnashing of teeth.

Then came Testacular: The spectacular test runner.
For a time, once everyone stopped sniggering like teenagers, it was good.
Unit tests ran quick as lightning on any browser that could call a web page.

Finally, to please the squeamish who were too embarrassed to speak of Testacular to colleagues and managers, the creator moved heaven and earth to rename it Karma.
And it was, and still is, good.

But there was still unrest.
While unit tests were as quick as the wind, E2E (end-to-end) tests were constrained from within the Javascript VM.
"Free me from this reverse proxy! Treat me as though I were a real user!"
And thus Protractor was born.

*ahem*
Protractor is the official E2E testing framework for AngularJS applications, working as a wrapper around Web Driver (ie. Selenium 2.0) which is a well established and widely used platform for writing functional test for web applications.  What makes it different from Karma is that Karma acts as a reverse proxy in front of your live AngularJS code, while Web Driver accesses the browser directly. So your tests become more authentic in regards to the user's experience.

One cool thing about Web Driver, which I didn't realise till recently, is that it's API is currently being drafted up as a W3 standard.  We're also seeing a number of services appear for running your selenium tests using their VMs, which is useful for doing CI and performance testing without taking on the operational overhead yourself.

Let's go!

The App

I've created a simple application to write tests for.  So first we'll clone the application from github, install the local NodeJS modules, and then install the required bower components:

git clone https://github.com/rolaveric/protractorDemo
cd protractorDemo
npm install
node node_modules/bower/bin/bower install

Now you should have a copy of the application with node modules 'bower' and 'protractor' installed, and AngularJS installed as a bower component.

The application is dead simple.  It has a button with the label "Click to reverse".  When you click it, it (you guessed it) reverses the label. So our tests should look something like this:

• Load App
• Click button
• Assert that label is now reversed
• Click button again
• Assert that label is now back to normal

Installing Selenium

Protractor comes with a utility program for installing and managing a selenium server locally: webdriver-manager
Calling it with "update" will download a copy of the selenium standalone server to run.

node node_modules/protractor/bin/webdriver-manager update

Setting up for tests

First thing we need is a configuration file for protractor.  It tells protractor everything it needs to know to run your tests:  Where to find or how to start Selenium, where to find the web application, and where to find the tests.

Since we're using webdriver-manager to run selenium server, we'll tell it the default address to find it: http://localhost:4444/wd/hub
Optionally you could give it the location of the selenium server JAR file to start itself, or a set of credentials to use SauceLabs.

The tests we'll place in "test/e2e", and npm start spins up a local web server at "http://localhost:8000/".  So the basic configuration file stored in "config/protractor.conf.js" looks like this:

exports.config = {
seleniumAddress: 'http://localhost:4444/wd/hub',
specs: ['../test/e2e/*.js'],
baseUrl: 'http://localhost:8000/'
};

There's actually a lot more you can do with the configuration file, but this is all we need to get going. Check out the reference config in protractor's github for more options.  You can do things like pass parameters to selenium, your testing framework, and even to your tests (eg. login details).

Writing tests

In "test/e2e/click.js" is a simple test for the "Click to reverse" behaviour:

The process behind writing E2E tests is pretty simple: Perform an action, get some data, then test that data.  Generally each action or query also involves finding a particular element on the page, either by CSS selector, ng-model name, or template binding.

First it opens the "index.html" file (which it finds relative to the baseUrl in the configuration file), finds the button by it's binding, clicks the button, then gets the button's text value and tests it.  Then we click the button again, get it's text value, and test that it's changed back to normal.

Running tests

Now for the payoff - the running of the tests.

First we'll start up the web and webdriver servers:

npm start
node node_modules/protractor/bin/webdriver-manager start

Then we tell protractor to run the tests according to our configuration file:

node node_modules/protractor/bin/protractor config/protractor.conf.js

If everything's gone well, you should soon be rewarded with the following result:

Finished in 2.061 seconds
2 tests, 2 assertions, 0 failures

And there you have it.  Webdriver tests for your AngularJS application with minimum pain.  If you already have angular-scenario based tests, converting them to Protractor should be a trivial "search & replace" exercise with the right regular expressions.

GopherJS: Go to Javascript Transpiler

In my last entry I talked about the idea of migrating from a legacy platform to a modern platform by implementing the new platform as a reverse proxy.  That way you can keep your existing platform active while gradually migrating over to the new platform with minimal risk; No need to maintain 2 code bases, and no need to keep your new code on the shelf collecting dust until you've finished porting everything else.  Then I demonstrating how you can do this using Go.

Amongst the feedback from the community (For which I say, thank you to everyone who read, shared, and commented.  It was much appreciated.  Let no one doubt how nice the online Go community is) was the question "What about your common libraries?".  It's a good point.  The reverse proxy solves the problem nicely when porting code route by route.  But you're likely to have some common libraries shared across multiple routes.  If you've only migrated some of those routes, you're going to be dual-maintaining both an old and a new version of that library until all your routes have been ported.

Maybe that's okay.  Maybe you're comfortable with the pace of your migration vs the need to make maintenance changes.  But if you're not in that position, you can use a transpiler to convert your code from the new language back to the old one.  For my situation of moving from Javascript to Go, that means using GopherJS.

GopherJS

GopherJS transpiles Go source code to Javascript, which means you can get all the development and build time advantages of Go (eg. Static type checking, built in code coverage tool, etc.) and then run it in a Javascript library like NodeJS or the browser.  The creator, Richard Musiol, has even setup a GopherJS Playground so you can give it a try online and immediately execute the code in your browser.  You can even use AngularJS.  In fact, that's what the playground uses, along with an AngularJS wrapper library, go-angularjs.

Naturally, there are some limitations. Like you can't run anything anything that requires cgo or anything that needs low level access to the OS (unless you build an adapter for NodeJS).  Even so, it's a pretty impressive list of core packages which are compatible.  And don't let the lack of "net/http" or "database/sql" access scare you away - you can still use existing Javascript libraries to fill those gaps, and I'm going to show you how.

Another thing you need to be aware of is that GopherJS produces Javascript suitable for an ECMAScript 5 (or ES5) compliant environment.  So if you're building code for an older Javascript environment, like IE8 or Windows Host Script, you're going to need shims for at least Object.keys(), Object.defineProperty(), Object.getOwnPropertyNames(), and the various Typed Arrays.

And last, you need to be aware that it's not an all access border between Go and Javascript.  If you want to pass a struct with methods from Go, you need to use "js.MakeWrapper()" to make those methods safe.  Similarly, you can't implement Go interfaces with Javascript objects.  You'll need an intermediary that accesses the Javascript object as a "*js.Object".

What does Go look like in Javascript?

First I'm going to show you what Go code looks like as Javascript.  We eventually want to take an existing Javascript library and convert it to Go, so we need to know what changes (if any) we should make to our code before porting it to Go.

You can see I've created a (rather contrived) Go package called 'pet' which defines a simple 'Pet' struct type, and a factory method called 'New()'.  Since 'Pet' includes a method, 'New()' uses 'js.MakeWrapper()' to make the methods safe to use in Javascript.  Then in 'main' I'm importing 'pet' and the 'github.com/gopherjs/gopherjs/js' package, which gives me access to Javascript context objects like the global scope.  So I attach the 'New()' factory under the namespace 'pet'.

Here's the result when built with GopherJS.

1470 LOC and 45kb, uncompressed and unminified.  The bulk of which is the builtin library.
It will only compile what it needs to.  So if you declare types that are never used, they won't show up in the resulting code.  This goes for core packages too.  If I change that code so it requires "fmt", the result explodes to 12845 LOC and 624kb ("fmt" imports a LOT of stuff).

Lets take a look at what the code we wrote looks like:

You can easily recognise the "pet" package from lines 10-36 in that extract. I wouldn't get too worried about what it's doing there. The important thing is that it's there.

One thing I will draw your attention to is our main method, specifically line 41.
It's creating a map and setting the value of "New" to the function "pet.New()". It's then passing that to "go$externalize" which is a helper method GopherJS uses for turning Go types into primitive Javascript types. Take maps as an example. In Javascript, map keys can only be strings. But in Go, they can be anything. So GopherJS uses it's own special "Go$Map()" type internally, and then tries to convert it to a standard Javascript object when passed to "go$externalize".

Then it's assigning our externalised map to "go$global.pet". "go$global" is an internal variable for referencing the global scope object in Javascript. You can see it being declared on line 2. If used in a browser, it will be equivalent to "window". Otherwise, it's whatever the "GLOBAL" variable currently is. If you're using a Javascript runtime that doesn't include either of these, you'll need to manually declare "GLOBAL" yourself.

Porting a Javascript library to Go

Now we've got an idea of what our Go code will look like when it's converted to Javascript, we can start thinking about how we're going to port a part of our Javascript code to Go without breaking the rest of our Javascript code.

Lets say we've got a 'User' model object which uses the global variable 'DB' to make SQL database calls:

Couple of things we know will be different when we convert this to Go.

1. The method names will start with an uppercase letter, otherwise they won't be exported.
   This isn't idiomatic for Javascript, but that's OK because we're not writing Javacript.  We're writing Go that runs as Javascript.
2. DB will need to be an interface, with a new function for registering a DB implementation.
   That way we can switch implementations for Go and Javascript.
3. In Go, "User" will be a type of struct, not a type of function.
   And while we can create methods for type instances, we can't create static methods like "User.new()". They'll need to go into the package namespace.
4. While it's possible to wraps all "User" objects with "js.MakeWrapper()" so we can access "user.Save()", that means we also have to create getters and setter for the regular properties.  Rather than add the extra boilerplate, "Save()" will be moved to the package namespace and take the "user" as a parameter.

With that in mind, here's what the refactored API looks like:

The main difference is the addition of the "registerDB()" method for registering a DB interface implementation, rather than finding it on the global scope.

Now to the Go code:

The "Save()" method required a "SaveJS()" wrapper to bridge the JS <-> Go barrier for the "user" object, and "RegisterDBJS()" does the same for the database adapter.  You can find the full working code examples at: https://github.com/rolaveric/gopherjs-demo

There you have it: A Javascript library written in Go with only a little tweaking to the original API.
And without compromising on the quality of our Go code either.

Conclusion

GopherJS bridges that gap between Go and Javascript quite nicely without compromising on quality.
There is a cost in the size of the generating code, but lets remember just how little is provided by Javascript's standard library compared to Go's core library.  And once you get past that initial bootstrap, there's definitely no issue with performance.

So if you're looking for a way to port away from Javascript to Go without dual-maintaining libraries, or if you're so enamoured with Go that you can't bare to write Javascript even for the browser, then GopherJS is for you.

UPDATE: GopherJS has matured since I originally wrote this article.  So with Richard Musiol's help, I've updated the examples to be more conscious of the Go <-> JS barriers.  I've also created a github repo with the examples so they can be tested from end to end.

Wading into Go

I first took notice of Go last year when I read this article about how Iron.io went from 30 servers down to 2 by converting from Ruby to Go.  Since then I keep peeking back at it, reading a bit more doco here, trying out the tour, and eventually attending the local Go meetups.  There I finally got my burst of inspiration to build a proof of concept for replacing an old enterprise backend I work with, built on Classic ASP, with Go.

The experience was quite fascinating for me because my primary language is Javascript, and my experience with modern server-side web frameworks is pretty shallow.  For example, the way I keep thinking of pointers vs values in Go is the same way I think of objects vs strings in Javascript.  The former is mutable, meaning it's possible to get side effects when it gets passed around, and the later is immutable.  It probably oversimplifies the difference, but it works for me.

The Plan

OK.  We're porting a legacy web application to a new platform.  What's the plan?

It'd be naive to say "X is better than Y, therefore we shall port all our Y to X immediately!" and leave it at that.  There's other questions we need to answer:

• How long will it take?
• What does all the X you've written do while you're still dependant on Y?
• What if there's just some things that Y can do which X can't (yet)?

The answers should be:

• "A long time" cause that's the truth
• "It gets used in production" because code has no value until it's used, and
• "Then you keep using Y for those things" because, as they say, "you don't throw out the baby with the bath water".

The plan is to use the new technology as a reverse proxy which, initially, takes all requests and forwards them on to your legacy back end.  Then, over time, you start porting features from the legacy platform to the new one.  If something goes wrong, you can turn off that route handler and let the legacy platform pick it up again.

Doing this in Go is trivial.  The core library already comes with a simple reverse proxy that suits our needs:

The Martini Web Framework

While the Go core library is very complete, especially for the building of web applications, there is still plenty of room to build libraries on top.  For example, while Go comes with the "testing" library and the "go test" and "go cover" commands, there's space for third-party libraries to define their own DSLs for writing tests, such as GoConvey.  In the same vein, there's plenty room for different web frameworks to implement different opinions and architectures.  My personal favourite is Martini.

Martini is a micro-framework, similar to Sinatra and Express.  It doesn't give you bells and whistles to plug into your application (well, not out of the box), but it does give you a simple way to define chains of request handlers (like filters, if you're coming from Java servlets) and pass values to handlers through dependency injection.

You can have common handlers, called middleware, which run against every request, and handlers for routes.  So you can have a common Authentication handler that identifies the user for every request, and then specific Authorization handlers for different routes that make sure the user has the required access before running the final handler.  Here's an example:

Here's what a request to this code looks like, with the flow of control through the request and response:

But how does the Authorization handler know what the result of the Authentication handler was?  That's where Martini's dependency injection comes into play.

It uses Go's reflect package to determine what types a handler is expecting as parameters.  By default it knows about the http.Request and *http.ResponseWriter objects, which is why Martini also works with any handlers designed for http.HandleFunc().

You can add your own injectables or services by calling the MapTo() method on the martini.Context (Another default injectable) for the request.  MapTo() takes a variable and the type that it should be injected for.  You can also use this to wrap existing services, as Martini does with the *http.ResponseWriter.

Impressions of Go

Now that you've got an idea of what I've been working on, here's some of the impressions that Go made on me.

A well stocked box of goodies

Out of the box, Go comes with a standard library to be proud of.  Take for example the fact that it comes with a simple reverse web proxy, ready to go.  It also comes with a set of packages for compression, including gzip, and 11 different packages for encoding, including JSON, XML, and Base64.  Normally I'd expect to go to third-party libraries or roll my own for at least a few of these.  Not in Go.

And let's not forget the 'go' command line tool itself, which can:

• Build
• Test
• Benchmark
• Calculate code coverage from tests
• Format code
• Fix code written for older versions of Go
• Host a web server for serving code documentation
• and retrieve dependant packages from Git and Mercurial repositories

The convention of using the repository domain as the package namespace is a great idea which keeps dependency management nice and simple.  The only drawback I've heard is that it doesn't support the ability to set specific revisions as a dependency, which will make it awkward if a third-party package introduces non-backwards compatible changes.  But there are examples of the community stepping up to fill the gap.

Another favourite feature of mine is "go fmt", and the way the formatting conventions are enforced by the compiler.  I am tired of arguments over code formatting, and I'm glad that the creators of Go have cut those arguments off at the knees, saying "This is how it is - deal with it.  Now, back to the show!".

Third-party support isn't perfect, yet

I had one third-party technology requirement for my Go program; It had to support MS SQL, because that's what the legacy platform was using for persistence.

go-wiki's list of supported SQL drivers included an ODBC driver which is cross-platform, using Free TDS for Mac and Linux, so I thought this wouldn't be a problem.  Sure enough, when I first tested it on Windows, everything seemed fine.  Then I did some benchmarks and realised every stored procedure call was taking a lot longer than it should.  When I tried the same calls with an ADODB driver (which I didn't want to use because it only works on Windows), I was getting much better speeds.

I haven't exhausted all my options yet to fix the issue yet.  For example I've only tested it on Windows, and I haven't explored whether connection pooling will help (I'm currently opening and closing a connection on each query).  But it's an unhealthy reminder that there's likely to be issues like this when moving from legacy platforms to something new like Go.  If I were using Postgres or a NoSQL database, there'd be no problem. But I'm not, and so there is.

Types: The good, the bad, and the "what the?"

Go uses strict typing, which can be a bit of a shock coming from a dynamic typing language like Javascript. Most of the time it makes perfect sense and you wouldn't have it any other way.  Here's a few common examples:

The simplest example possible - a function that expects a number rather than, say, a string.

Unlike Java but similar to Scala, Go treats functions as first class.  This means you can pass functions as parameters to other functions, and return them as results.  But you don't want just any old function, you want one which matches your callback schema: message string as a parameter, and an error (if any) as the result.

One thing that's unique to Go is the way it handles interfaces.  They're implemented implicitly.  So an interface becomes a way of saying "I need 'something' which can do X" rather than "I need a Y, which is 'something' that can do X".  Anything can say "I can do X" will be accepted, and can be declared without even know what a "Y" is.

Interfaces also give us a way to cheat the typing system entirely.  An empty interface can be implemented by anything.  So if we have a function which expects an empty interface, we can pass anything to it.  Or we can have a slice (Equivalent of a Javascript Array) of empty interfaces, which can store anything.  But that just means we need to use type assertions when we try to do something with that value, otherwise we could end up trying to get the substring of a number.

Here's an example which did my head in a bit at first.
The Rows.Scan() method in the database/sql package expects a slice of empty interfaces, which are the destination for the values found in the current row.  Empty interfaces can be anything, right?  So a slice of empty interfaces can contain anything.  That makes sense because you could have numbers, strings, dates, etc. all returned in the same row.

The SQL driver I'm currently using returns everything as strings.  So I thought "OK, I can just pass in a slice of strings.  Strings can be empty interfaces, so therefore a slice of strings can be a slice of empty interfaces, right?

Wrong.

It's not the containers that can be anything, it's the contents.  A container for strings and a container for anything are two different things; If I ask for one, I don't expect the other.
In this example of Rows.Scan(), you can get around it by loading a slice of empty interfaces with the pointers from a slice of strings.

Thankfully this example is the exception, not the rule.  And it demonstrates that if the typing system does start to restrict you, there are ways to bend it to your will.  But it's always better to discover a problem at compile time than run time.

New language insecurity

This isn't really related to Go, it just happened to be the unknown language that I was trying.

I found that doing things in Go took 3-4 times longer than it would have done in Javascript.  When working on something in Javascript I would simply plan it out, and then implement it.  In Go I would plan it out, implement half of it, then go back to the plan, then start implementing from scratch, then back to the plan, then redo the original implementation.

This isn't because there's anything wrong with Go or right with Javascript.  It's because I'm experienced with Javascript and inexperienced with Go.  Experience doesn't just bring competence, it also brings confidence. When I was restarting my work in Go, it's not that it wasn't working, it's that I would start second guessing the design.  "Should that have been a type? Or maybe an interface?  Maybe I should just split these into separate packages... or, maybe less packages?".

Sometimes you need to put your head down and say "If it compiles and my tests pass, that's good enough for me!". You can always comes back to it later when you've: a) Got a more experienced Go developer to critique your work, or b) enough hours reading other people's Go code to form your own opinions.

Conclusion

Coming from Javascript world, Go is an intriguing place that I'd like to get to know better.  The core library is very complete and powerful, though somewhat dry at times.  But this allows the community to build on top of it with their own opinions, like how Martini builds on top of net/http, or GoConvey on top of testing.

If you're interested in Go but haven't found the excuse to give it a try, my advice is: Find that excuse. Rewrite something, anything, just to get a taste for it.  If people at your company are dismissive of the idea, then practices a little "Constructive Disobedience" and do it anyway.  "You decide your own level of involvement".

Unit Testing AngularJS

It's not always obvious how to write automated tests for the different components in AngularJS, so I'd like to share some of my techniques for testing AngularJS applications.

Automated Testing Stack

If you've got absolutely no automated testing setup at all, then I recommend looking at using one of the following to give you some scaffolding: angular-seed, Yeoman, or ng-boilerplate.

Here's a quick overview of each piece of the unit testing stack.

Karma: The Test Runner

Karma does the work of starting our browser(s), running the tests, and reporting the results in whatever format we desire.  It can also handle pre-processing code for doing things like compiling CoffeeScript or injecting Code Coverage markers.

Jasmine: The Test Framework

We need a format to write our tests in.  The default one used by the AngularJS community, and what I'll be writing the rest of this article with, is Jasmine.  It uses a BDD (Behaviour Driven Development) style, which essentially means it tries to make your tests read like business specifications that an analyst could understand.

Here's a quick example of a Jasmine test:

The "describe()" method is used to group tests.  The "it()" method is the specification: a descriptive string for the spec, and a function for testing that spec.  The "expect(value).toSomething()" is an assertion.  You pass a value to "expect()" and then you run what's called a 'matcher' method against it.  You can also run setup and teardown code using "beforeEach()" and "afterEach()" methods.

Karma has an adapter for interpreting the results from Jasmine, which it can then feed into various reporters.  So if Jasmine isn't your poison, chances are there's an adapter out there for whatever testing framework you prefer.

ng-mocks: The Helper Library

If you've ever downloaded AngularJS as an archive, you may have spotted the angular-mocks.js file.  This contains the ngMock module, which provides a set of helper functions to make your testing life easier.  Particular the inject() method which you can pass a function with injectable parameters (eg. Services), and it will handle all the dependency injection for you.

Services

Alright.  Down to the actual testing.
I'm going to start with the simplest example.  This will work for anything produced with "module.value()", "module.constant()", "module.factory()", or "module.service()".

The relevant parts for AngularJS developers is "module()" and "inject()".

The best way to think of the "module()" function is that it's doing the same job as the "ng-app" directive - it bootstraps that module so you can inject it's components.  The great thing is that the scope for that module only lasts for a single test.  So changes you make in one test won't have an effect on the next test.

The "inject()" method hooks into Angular's dependency injector.  So you can pass it a function with your dependencies, and it will handle their injection for you.  Although it won't work if the module those components belong to has not been loaded yet by "module()".

Here's a more verbose example; a pattern which I often use myself:

Handling Dependencies

I try not to make any function calls in my service constructor.  This makes things simpler if, for example, I depend upon another service which I want to mock during testing (It is called "unit" testing for a reason).  Lets say "myService.myMethod()" called "anotherService.anotherMethod()".  Rather than test what "anotherMethod()" does within the test for "myMethod()", I just want to confirm that it gets called.  I can do this by getting an instance of "anotherService", using "inject()", and replace "anotherMethod()" with a spy which tracks if and how it gets called:

If "myService" was using a method from "anotherService" in it's constructor, that would make things trickier, but not impossible, to test.  Services are constructed only when they're first injected (no point constructing something that's not even being used).  So the trick is to inject "anotherService" first, set up your spy, then inject "myService".

You couldn't do this if your constructor was calling one of it's own methods (eg. "myService.init()").  So when you're writing a complex constructor for a service, or controller, you really need to sit back and think "How am I going to test this?".

Filters

Filters are just functions.  The key to testing them is to get yourself a reference to those functions.  This is simple with "inject()".  You should set a parameter with the name of your filter with the suffix "Filter".  Here's an example:

Alternatively you can use the "$filter()" function, like so:

Controllers

Now we're getting somewhere interesting.  Controllers are different to services in that their dependencies aren't just services - they can be "resolve" values, such as "$scope".  On top of that, not all controllers just attach properties to "$scope".  Some will attach properties to themselves through "this".  2 examples are using controllers for directive to directive communication, and the new 'ng-controller="MyCtrl as scope"' optional syntax for controllers being introduced in AngularJS v1.2

So we need a way to inject specific dependencies into our controller, and then we (may) need a reference to the instance of that controller function.  The way to achieve this is to use the $controller service:

That works if you're not doing much with the $scope except for attaching properties.  But what if I'm using some of the built in functionality for scopes like "$watch", "$on()", "$broadcast()", or  "$emit()"?  You could create spies to mock all these things.  I personally like to use a real $scope object.  So how do I get one?  Inject "$rootScope" and call "$new()" on it:

Here's my template for controller tests:

Directives

The key to testing directives is to use the $compile service to compile a DOM element which includes your directive.  $compile will trigger your directive's code, and you can then start querying the DOM element and scope to test it's behaviour.
Here's a simplified version of the ng-hide directive (Similar to the original, but without $animate support):

To test it, we need to compile the directive, and then test how the element reacts when we change the scope or trigger use actions.
Here's a test taken straight from the AngularJS source code (The best source for writing and testing directives):

Walking through it, first it uses jqLite/jQuery to create a DOM element with the directive.
Then it passes the element to the $compile service, along with a scope object (in this case $rootScope), which runs the code for any directives it finds.
Then it tests that the element is still visible, since "exp" is undefined and therefore falsy.
Then it sets "exp" to "true", triggers the digest loop so that the $watch gets run, and then tests that the element is now hidden.

Most of your directive tests are going to follow this pattern some how:

1. Create a DOM element with your directive.
2. Pass it to $compile(), along with a scope object.
3. Change the scope.
4. Query the DOM for changes.

Providers

A provider is really no different from a service, except that it requires a special "$get()" method for "providing" the dependency, and it can exist during the "config" phase of AngularJS' lifecycle.
The trick is getting a reference to the provider in pristine condition (ie. Before "$get()" is called).  The way you do this is using the "module()" helper function, provided by ng-mocks:

In this scenario we have a provider called "myServiceProvider", which belongs to module "myModule".
We use the "module()" function to instantiate "myModule", and then get a reference to "myServiceProvider".
However, calling "module()" alone is not enough.  It doesn't actually do anything until "inject()" is called.  So we just call "inject()" with no dependencies, meaning "myServiceProvider.$get()" has still not been called.

Conclusion

AngularJS has been built from the ground up with testing in mind, but it's not always immediately obvious to new comers as to how they might test a particular component.
But once you know the trick, the pattern to adopt and the services to call, there's nothing to stop you writing a suite of tests you can rely on.
Then library upgrades become a trivial matter of: drop in the new version, run the tests, and fix any failures.  I couldn't use the weekly AngularJS builds without it.

5 Reasons to use AngularJS

Post republished to https://legacy-to-the-edge.com/5-reasons-to-use-angularjs/

I've been using AngularJS for about a year now, and I think it's safe to say that it's one of the best things to happen to me as a web developer.  It's made UI development faster, safer (ie. testable), and more enjoyable for me then ever before.  And by studying it's source code and taking up it's techniques and philosophies, it's made me a better programmer outside of AngularJS too.

If you haven't heard of AngularJS, go to their home page right now, read through the blurbs, have a quick toy with the demos, then come back.  If you're not sold on it already, read on and I'll tip the scales for you with 5 reasons to start using AngularJS for all your web development work - especially if you're working with a legacy system.

1. Less work for the same result

The story behind how AngularJS went from a hobby project developed solely by +Miško Hevery to being a Google sponsored open source project is that Misko went to his manager, +Brad Green, and said "You know, I bet I could rewrite our current project in Angular in 2 weeks.".  It took 3 weeks and the lines of code went from 17,000 to 1,500.

The key behind such a massive reduction in code is AngularJS's declarative approach to data-binding on the UI.  Lets start with a simple example.  I want a text input to update the message in another part of the DOM. Here's how I might do it:

Now compare to the same thing done in AngularJS:

Done.
I have simply declared "Here's my application, here's an input that binds to 'message', and here's somewhere to output 'message'."
The "How" is left entirely to the directives to determine.

It's a contrived example, but it demonstrates the advantage of a declarative approach: Stating the "What?" and then letting the framework handle the "How?".

The same can be said for dependency injection.  When I'm writing a controller, I don't tell it where and how to get the '$log' service.  I just declare "I need the service called '$log'".

2. It thins out your server-side code

Angular takes care of templating and routing your views, which is generally a non-trivial chunk of your server-side processing and code maintenance.  You can entirely decouple your client application, leaving the server to serve and consume JSON data.

This provides a great opportunity if you've been thinking of switching or experimenting with different backends.  Lets say your backend is written in Ruby on Rails, but you're interested to see how it would perform with Groovy on Grails instead.  You can write your front-end in Angular with a RESTful server API, then swap out your backend with something that serves that same API.  It's no small thing to rewrite a whole back-end, but it's a hell of a lot easier when you don't need to worry about the UI.

3. Testing is trivial

AngularJS was written from the ground up to be testable.  Dependency injections lets you slip in mock versions to work with.  Directives can be triggered by using $compile on HTML strings.  HTTP responses can be imitated with a mock $httpBackend service.  And all of this without actually attaching anything to the DOM, meaning your tests run lightning fast.

The barriers to testing AngularJS applications are only as high as you choose to make them.  You're writing less code, so you have the time to write tests from the start.  Sometimes you may feel that writing your mocks takes so much effort that it's impractical.  That's a sign that either you need to take a closer look at the documentation for Jasmine 'spies', or you need to rethink your design ("Why does this single unit of code need so much 'stuff'?")

4. Your user experience is more responsive

You don't always notice just how much time is taken changing from one page to another, on the web.  Sometimes that's to be expected, such as when moving from a completely different 'site' to another.  But when you're moving from one page to another, within the same site, with almost the exact same headers and footers, CSS includes and Javascript libraries, it should only take as long as is required to load the HTML which has changed.

With a SPA (Single Page Application), like Gmail, you have some initial load time on your first visit, but then content changes within that application are near instantaneous.  You can manage this easily with AngularJS's built in URL routing and ng-view directive.  And if that's not sophisticated enough for your needs, you can use ui-router to define your application in terms of a state machine with nested views.

5. Great community

Last, but far from least, is the AngularJS community.  There's no shortage of resources for learning Angular (eg. egghead.io, yearofmoo), places to ask questions or just 'stay in the loop' (eg. Google Groups, G+ Commmunity, IRC Channel, Meetups), and open source projects for improving Angular development (eg. Angular UI, Yeoman generator, ng-boilerplate).  Everyone I've interacted with in the community has been helpful and constructive with their criticisms.  Angular would not be seeing the success it has without such positive community contributions.

If that hasn't convinced you - power to you, you must have a damn nice set up already.
If your curiosity is piqued, but you still have concerns, visit the G+ Community or IRC channel.

Cheers,

Jason Stone