Angular 2 with Babel

May 8, 2016 - JavaScript, Angular 2, Babel

Although Angular 2's primary language is apparently TypeScript, many people want to use Babel as shown in a survey.

However, The official documentation targets only TypeScript and ES5. In addition, many pages are not yet available for ES5. That is because Angular 2 relies heavily on cutting-edge ES7 decorators and TypeScript's type annotations for annotating components and services.

To fill the gap, you can use babel-preset-angular2 that supports all the decorators and annotations available in TypeScript. With the preset, you can follow the official documentation for TypeScript to learn Angular 2 itself.

How to use it

npm install -D babel-preset-es2015 babel-preset-angular2

Add presets to .babelrc. Note that the presets' order is important.

{
  "presets": ["es2015", "angular2"]
}

See babel-angular2-app for more complete example.

Supported annotations

Name	Example	EcmaScript	TypeScript	Babel*	Babel + angular2
Class decorator	`@Component()`	Stage 1	Yes	Yes	Yes
Property decorator	`@Input()`	Stage 1	Yes	Partial*	Yes
Parameter decorator	`@Optional()`	Stage 0	Yes	No	Yes
Type annotation	`foo: Foo`	-	Yes	No	Yes

"Babel*" above means Babel with the following official plugins:

babel-preset-es2015
babel-plugin-transform-class-properties
babel-plugin-transform-decorators-legacy (not literally official but maintained by @loganfsmyth, one of Babel's core contributors)

Property decorator in Babel is marked "Partial" because babel-plugin-transform-decorators-legacy ignores class properties without initializers.

You can emulate parameter decorator and type annotation with plain ES2015 like the following but it's a little bit counterintuitive.

class HelloComponent {
  constructor(foo: Foo, @Optional() bar: Bar) {
    // Do something with foo and bar.
  }
}

class HelloComponent {
  static get parameters() {
    return [[Foo], [Bar, Optional()]];
  }

  constructor(foo, bar) {
    // Do something with foo and bar.
  }
}

Polyfills

Angular 2 beta versions had polyfill bundles but RC versions don't. But never mind. We can just import them before bootstrapping our app.

npm install -S babel-polyfill zone.js

src/index.js

// Import polyfills.
import "babel-polyfill";
import "zone.js/dist/zone.js";

// Bootstrap app!
import { provide } from "@angular/core";
import { bootstrap } from "@angular/platform-browser-dynamic";
import { ROUTER_PROVIDERS } from "@angular/router";
import { LocationStrategy, HashLocationStrategy } from "@angular/common";

import { HelloApp } from "./app";

bootstrap(HelloApp, [
  ROUTER_PROVIDERS,
  provide(LocationStrategy, { useClass: HashLocationStrategy })
]).catch(err => console.error(err));

Note that we can use babel-polyfill that includes core-js instead of es6-shim and reflect-metadata. According to use core-js instead of es6-shim, we can use whatever ES6 + ES7 polyfill we like.

Module resolution

You can use any module resolver as long as it works with Babel. I'll pick Browserify here for its simplicity.

npm install -D browserify babelify

Add a build script to your package.json assuming that your bootstrap script locates at src/index.js.

{
  "scripts": {
    "build": "browserify -t babelify src/index > public/bundle.js"
  }
}

npm run build

Isn't this simple? babelify automatically finds your .babelrc and uses the presets specified above.

Of course you can use other module resolvers like Webpack or SystemJS.

Offline compilation

This is not yet available for Babel. Not completed even for TypeScript.

The compiler_cli seems to be deeply integrated with TypeScript compiler. It statically collects metadata from the source and feed it to the compiler. I believe that it is achievable with Babel to do the same thing.

I'm thinking of working on it once the TypeScript version is published and the compiler API becomes more stable.

Conclusion

I've presented how to use TypeScript-specific annotations in Babel. You can enjoy Angular 2 with your favorite transpiler.

See babel-angular2-app for more complete example.