Angular 2 expression parser and ng-init directive

Question

Basically I'm looking for a way to implement a counterpart to Angular 1.x ngInit directive.

I'm aware of ngOnInit hook and the fact that it is the recommended place for initialization code. I consider ngInit directive a quick, declarative way to prototype or fix a component that shouldn't be generally used in well-written production code (although a developer has the right to choose what's best for him/her).

Doing something like that in init dummy directive

<p [init]="foo = 1; bar()"><p>

evaluates the expression more than one time and causes

Template parse errors:

Parser Error: Bindings cannot contain assignments

error.

In Angular 1.x it could be done just with

$parse($attrs.init)($scope)

How can Angular 2 parser be used and possibly extended to evaluate foo = 1; bar() foo = 1; bar() template expression on component initialization?

Answer 1

Just a Workaround ( Plunker Demo ), see estus 's answer for a solution

init Directive:

@Directive({
  selector: '[init]',
  inputs: ['init']
})
export class InitDir {
  init;

  ngOnChanges() {     // `ngOnInit` if you want it to run just once
    if(this.init){
      let iife = function(str){ return eval(str); }.call(this.init[0], this.init[1]);
    }
  }
}

Usage:

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2 [init]="[this, 'this.name = 1; this.bar();']">Hello {{name}}</h2>
    </div>
  `,
})
export class App {
  constructor() {
    this.name = 'Angular2 (Release Candidate!)'
  }

  bar() {
    alert('Yo Bar!');
  }
}

Answer 2

This can be achieved with a directive:

@Directive({ selector: '[initialize]' })
class InitializeDirective {
  @Output() initialize = new BehaviorSubject();
}

The expected use is:

<div (initialize)="initViaMethodCall(); foo = 'init via assignment'"></div>
<ng-template (initialize)="bar = 'init with no extra markup'"></template>
{{ foo }}
{{ bar }}