Exploring the capabilities of the Angular 2 expression parser alongside the functionality of the

Question

Exploring the capabilities of the Angular 2 expression parser alongside the functionality of the

Is there a way to create an equivalent of the Angular 1.x ngInit directive in Angular 2?

I am familiar with the ngOnInit hook, which is recommended for initialization code. The ngInit directive seems like a quick and declarative way to prototype or fix a component, even though it may not be suitable for well-written production code (but every developer has their own preferences).

If I try something like this in a dummy init directive:

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

The expression gets evaluated more than once and results in the following errors:

Template parse errors:

Parser Error: Bindings cannot contain assignments

In Angular 1.x, I could achieve this using:

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

So my question is, how can we leverage and possibly extend the Angular 2 parser to evaluate the foo = 1; bar() template expression during component initialization?

javascript angular typescript angular2-template angular2-directives

Answer 1

Answer №1

Check out this workaround method demonstrated in the Plunker Demo. For a more detailed solution, refer to estus's answer.

`init` Directive:

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

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

How to Use:

@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

Check out this workaround method demonstrated in the Plunker Demo. For a more detailed solution, refer to estus's answer.

`init` Directive:

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

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

How to Use:

@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 3

Answer №2

To accomplish this, you can utilize a custom directive:

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

Here is how you can use it:

<div (initialize)="initViaMethodCall(); foo = 'initialized via method call'"></div>
<ng-template (initialize)="bar = 'initialized with no additional markup'"></template>
{{ foo }}
{{ bar }}

Answer 4

To accomplish this, you can utilize a custom directive:

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

Here is how you can use it:

<div (initialize)="initViaMethodCall(); foo = 'initialized via method call'"></div>
<ng-template (initialize)="bar = 'initialized with no additional markup'"></template>
{{ foo }}
{{ bar }}

Exploring the capabilities of the Angular 2 expression parser alongside the functionality of the

Answer №1

`init` Directive:

How to Use:

Answer №2

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Exploring the capabilities of the Angular 2 expression parser alongside the functionality of the

Answer №1

init Directive:

How to Use:

Answer №2

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`init` Directive: