在 Angular2 中访问 Typescript 对象变量

Question

How do I display the id and title of the below Hero object? The Hero interface below is mapped according to Firebase JSON response.

hero.component.ts

import {Component, Input} from 'angular2/core';
import {Hero} from '../model/hero';

@Component({
  selector: 'hero-component',
  template: `
                {{hero | json }} this works. This display the Firebase JSON response as seen below 
                <br>
                {{ Object.keys(hero)[0] }} this DOESN'T work
                <br> 
                {{ hero[Object.keys(hero)[0]].title }}this also DOESN'T work
  `
})

export class HeroComponent {
  @Input()
  hero:Hero;
}

hero.ts

export interface Hero {
  [id: string]: {
    createdAt: number;
    isActive: boolean;
    title: string;
    updatedAt: number;
  }
}

Firebase JSON response

{ "-KEMOfA5KFK98AXNhPY0": { "createdAt": 1459607745222, "isActive": true, "title": "Wind Hero", "updatedAt": 1459607745222 } } 

Answer 1

update

instead of pipes: [KeysPipe]

use

@NgModule({
  declarations: [KeysPipe],
  exports: [KeysPipe],
}
export class SharedModule{}

@NgModule({
  ...
  imports: [SharedModule],
})

original

You can't use Object.keys(hero)[0] in the template. No global references can be used, only members of the component.

Instead create a function on your component

getKeys(obj) {
  return Object.keys(obj);
}

and then in the template

{{ getKeys(hero)[0] }}

Alternatively you can build a pipe that extracts the keys like for example https://stackoverflow.com/a/34074484/217408

@Pipe({ name: 'keys',  pure: false })
export class KeysPipe implements PipeTransform {
  transform(value: any, args: any[] = null): any {
    return Object.keys(value);
  }
}

then use it like

{{ (hero | keys)[0] }}

Don't forget to add the pipe to pipes: [KeysPipe] on the component where you want to use it or alternatively

bootstrap(App, [provide(PLATFORM_PIPES, {useValue: KeysPipe, multi:true})]);

Answer 2

Your code isn't working since Object isn't available in your component.

You could try something like this:

@Component({
  selector: 'hero-component',
  template: `
            {{hero | json }} this works. This display the Firebase JSON response as seen below 
            <br>
            {{ obj.keys(hero)[0] }} this DOESN'T work
            <br> 
            {{ hero[obj.keys(hero)[0]].title }}this also DOESN'T work
  `
})
export class HeroComponent {
  @Input()
  hero:Hero;

  obj = Object;
}

or using a method like Günter suggested in his answer.