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.

AngularDart: The future of AngularJS?

The AngularJS team have been working on a port to Dart called, naturally, AngularDart.
They've taken the opportunity to completely rewrite Angular, adding features and patterns which feel quite natural when written in Dart.
At ng-conf 2014, they talked about their intention to port these new features back into AngularJS as part of version 2.0.  So I've been curious to take a look at AngularDart as a sneak peek into the future of AngularJS.

What's Dart?

Dart is an open source language, backed by Google (In the same way Go is), which is designed to replace Javascript as the programming language for web browsers.  It has it's own VM called Dartium, similar to V8 for Javascript, and I believe has some of the original V8 developers working on it.

But since the only browser which comes with Dartium is a special build of Chromium made specifically for Dart development, the Dart SDK comes with dart2js: A transpiler that produces Javascript which can be used in any browser that supports ECMAScript 5.

And the performance from what dart2js produces is fairly impressive.  Though one should always take benchmarks with a grain of salt.

What makes Dart different from any other modern programming language?

There are more transpilers to Javascript than you can poke a stick at.

I think the answer is about the original purpose of the language.  The purpose of Dart was to create a new language for web browsers, which requires it to have a resemblance to Javascript, so that it can interoperate with it.  This is different from, say, Clojure which wasn't written specifically so it could work with Javascript; That was implemented later as ClojureScript.

CoffeeScript is probably the closest example to what Dart is trying to do.  The difference is that CoffeeScript's purpose was always to be compiled down to Javascript.  It was never intended to completely replace Javascript, just to smooth out it's flaws.

Dart also comes with it's own tools.  As well as the dart2js transpiler, you've got pub for package management (think npm and bower), dartanalyzer for linting, docgen for documentation generation, and dartfmt for code formatting.  I'm a big fan of platform enforced formatting.  It takes the decision, and therefore the argument, as far away from me as humanly possible.

First look at AngularDart

"Hello Dart"

The Dart SDK comes with Dart Editor, a customised Eclipse IDE.  The welcome page includes a link for an AngularDart sample (which you can find the source for at github.com/angular/angular.dart), but it just wouldn't be as fun to have everything pre-done for us... well, not the first time, at least.

Go "File -> New Application", pick "Web application" and give it a name (I went with 'intro').  You'll be given some basic boilerplate: a ".dart", ".css", and ".html file, and some files used by 'pub' for package management.  Click "Run" (the green 'play' button) to spin up the application in Dartium.

What you should see is a simple page with the words "Click Me!" which reverse themselves when clicked.
The code is pretty self-explanatory.  It uses "querySelector()" to pick the element, set the text, then add an event listener which reverses the text.  Next we'll change it to use AngularDart instead of the core library.

"Hello AngularDart"

First thing we need is to install the AngularDart package using "pub".

Open up the "pubspec.yaml" file.  You should see an existing "browser: any" dependency.  This means the application depends upon any (ie. latest stable) version of the "browser" package, which is a library for applications that run in a browser, as opposed to using the "io" package if you wanted to run it as a standalone application.  Add "angular: any" to the dependencies and then run "pub get".

Back to the code.
First, lets import AngularDart and bootstrap it:

If everything has gone fine, this should have zero effect on your application. But if you start getting "The built-in library 'dart:json' is not available on Dartium.", run "pub upgrade" to fix it. It means one of the dependencies is still trying to use "dart:json" instead of "dart:convert".

Now we want to replace that click event listener with a directive.  Directives in AngularDart are given a CSS selector, rather than a name plus a type restriction.  However that doesn't mean they support any kind of CSS selector.  You're generally restricted to an attribute or element name.  So we want to change the "#sample_text_id" in the HTML to "[sample-text-id]", since we can't use the 'id' attribute:

Now to write our directive.

Directives are structured differently in AngularDart.  Instead of POJ objects, they're classes with an "@NgDirective" annotation.  Annotations play a big part in AngularDart, and are likely going to do the same for AngularJS 2.0 (Which is causing some contention since annotations aren't part of the ES6 spec, but is supported by Traceur).

Another big difference with AngularDart directives is that you don't use a name and a "restrict" property to decide what elements or attributes they get triggered by.  Instead you add a "selector" with a CSS selector to the annotation.

And last of all we need to make sure the directive gets included in the application bootstrap process. We do this by setting our new "ReverseClickDirective" class as a type on a new module, which gets passed into the "ngBootstrap()" method call.  I'll go into the Module class a bit more later.

All I've done here is a bad recreation of "ng-click", but it gives you an idea of how different AngularDart is compared to AngularJS v1.*, and how different AngularJS v2.* is likely to look.

In depth AngularDart

So you think "hmm, that's some what interesting.  Where should I go from here?".

A wise man once said "Luke, read the source".
The documentation for AngularDart is pretty sparse right now (understandably, since it's still in beta). So your best bet is to go straight to the source code, most of which is pretty well documented with inline comments; especially the public API.

Dependency Injection

In AngularDart, the DI framework has been separated from Angular into it's own package.  But it's still reference quite heavily in the Angular code, so you'll need to understand the DI framework to follow the AngularDart source code.  Remember the "Module" class with it's "type" method that was passed to the "ngBootstrap" method?  That was from the DI package, not from Angular.

Lets start with the Module class because it's really the most important class.  Open up "packages/di/module.dart".  Remember the "value()", "factory()", "service()", "constant()" and "provider()" module methods in AngularJS?  Here they are again, but instead you have:

• value(Type id, value, {Type withAnnotation, Visibility visibility})
  The "value()" you know and love, but with a twist.
  Instead of "id" being a string, it's a Type (ie. class).  This makes perfect sense in Dart because it supports an (optional) type checking system with classes.
  However, if you're not dealing with a class or you're dealing with multiple instances of the same class you can use annotations, combined with the "withAnnotation" parameter.
  
  The "visibility" parameter is a function which takes 2 injectors, the requesting and the defining, and returns whether or not the requesting injector has visibility of the instance created by the defining injector.  This is a new DI concept for Angular which we haven't seen in AngularJS v1.*, but was hinted at by Vojta Jina in this talk at ng-conf.  This idea of multiple injectors which can share, or not share, certain injectables is pretty cool.
• type(Type id, {Type withAnnotation, Type implementedBy, Visibility visibility})
  We've seen type before when we declared our directive class during bootstrap.  It's pretty much what you would expect - give it a class, and expect to get an instance of that class on injection.
  As an added bonus, you can also specify an "implementedBy" subclass to use when the "id" class is required.
• factory(Type id, FactoryFn factoryFn, {Type withAnnotation, Visibility visibility})
  If you're not a fan of "new", you can use a factory function instead.
  
  A "FactoryFn" accepts an injector as a parameter, for loading dependencies, and returns the injectable value.
• install(Module module)
  Used to extend an existing module.

What about "constant()" and "provider()"?
AngularDart has taken the whole "config() phase vs run() phase" concept and thrown it away, making those methods redundant.  If you really need to perform extra configuration on your modules before the application starts running, then you should do it before calling "ngBootstrap()".

Okay, that handles registering injectables.  But how do I declare dependencies?
"factory()" already has this handled because it gets an instance of the injector.  So it just needs to call "injector.get(MyDependency)", and away it goes.
What about "type()"?  Well that's the beauty of a static type system.  The DI framework uses reflection to determine the types expected by the class constructor, and injects those in.  Look at this:

That's how the DI framework works. If it's instantiated through the DI framework, then it will attempt to provide all the dependencies required by it's constructor.

Controllers, Filters, and Directives (Oh my?)

The missing methods from our old AngularJS modules are "controller()", "filter()", and "directive()".

The truth is that they've already been covered by "Module.type()" because, to the DI framework, they're just classes.  The way to declare them differently is to use annotations.

Filters use an "@NgFilter(name)" annotation, where the name is how they're named in the template, and expose a "call(input, params...)" method.

Controllers use an "@NgController(selector, publishAs)" annotation, which is actually a subclass of the @NgDirective annotation class.  "selector" is a CSS selector which is used to apply the controller to the HTML view.  And "publishAs" is the name that the controller instance can be referenced as from the template.  Remember the "ng-controller='x as y'" syntax in AngularJS? same thing. Properties from the controller instance are exposed on the view, and any dependencies declared in the constructor are injected in, including Scope for creating watchers and generating events.

I already showed you a basic directive example, but there's a lot more to be learnt.  If you want to go deeper, I suggest doing the same thing as for AngularJS: Look at the builtin directives.  I also suggest looking at the classes for the annotations too.
There's lots of interesting things, like implementing "NgAttachAware" and "NgDetachAware" to run "attach()" and "detach()" methods when scopes are first created and destroyed.

Components?

There is one new feature of AngularDart which I haven't covered which is a 'component'.
AngularDart components are related to web-components and make use of the Shadow DOM feature in modern browsers; Two things which I am not completely familiar with.  So I'm going to leave them alone for now rather than do them a disservice through my own ignorance.

Final Thoughts

First, Dart.  I'm so-so about Dart.
On one hand, trying to replace JavaScript with something more up to date is a noble ambition.
However Dart, and it's sponsor Google, have failed to win the rest of the web over.  The popular vote is in improving Javascript, rather than outright replacing it, through new standards like ES6 and ES7.
What's the best path?  I can't say.  But the writing on the wall tells me the support for Javascript is (strangely) growing, due in no small part to the success stories being heard about NodeJS.

As for AngularDart, the differences from AngularJS seem to depend on 2 main features: static typing with reflection, and annotations.
ES6 will introduce classes, but there's no suggestion that there will be any optional type checking added to go with it.  That means we can't just pass a class or function into the DI framework as they are (at least, not post-minification).  We'll still need that separate list of injectable types, but instead of strings it should be possible to use classes.
Annotations on the other hand aren't mentioned in any of the ES6 specifications at all.  They're an entirely separate feature which just happens to be in Dart and supported by Traceur.  So if AngularJS v2.* does use annotations, we're either going to be forced to use Traceur, regardless of the browser support for ES6, or we'll have to write them by hand:

Doing them by hand isn't so bad, but it does "kill the mood" some what.  The idea is to improve the syntax, but ends up making it worse.

Aside from those 2 worries, I'm quite keen to see what happens with AngularJS v2.*.
Now to get those last few IE8 users to upgrade...

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.