Exploring TypeScript Object Properties in Angular 2

Question

Exploring TypeScript Object Properties in Angular 2

How can I extract and display the ID and title of the Hero object below? The structure of the Hero interface is based on a 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 code works fine. It shows the Firebase JSON response below.
                <br>
                {{ Object.keys(hero)[0] }} - this part does not work as expected.
                <br> 
                {{ hero[Object.keys(hero)[0]].title }} - nor does this section work correctly.
  ``
})

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 } }

json typescript firebase angular

Answer 1

Answer №1

revision

Instead of using pipes: [KeysPipe], you should:

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

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

original version

Avoid using Object.keys(hero)[0] in the template as only component members are allowed, not global references.

Instead, create a function within your component:

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

and then utilize it in the template:

{{ getKeys(hero)[0] }}

Another option is to develop a pipe that extracts keys such as the one provided at

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

Utilize the pipe like this:

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

Remember to include the pipe in pipes: [KeysPipe] within the component where it will be used or alternatively add:

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

Answer 2

revision

Instead of using pipes: [KeysPipe], you should:

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

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

original version

Avoid using Object.keys(hero)[0] in the template as only component members are allowed, not global references.

Instead, create a function within your component:

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

and then utilize it in the template:

{{ getKeys(hero)[0] }}

Another option is to develop a pipe that extracts keys such as the one provided at

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

Utilize the pipe like this:

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

Remember to include the pipe in pipes: [KeysPipe] within the component where it will be used or alternatively add:

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

Answer 3

Answer №2

The issue with your code is that Object is not accessible in your component.

To resolve this, you can consider the following approach:

@Component({
  selector: 'hero-component',
  template: `
            {{hero | json }} - This line works and displays the Firebase JSON response below 
            <br>
            {{ obj.keys(hero)[0] }} - This line does not work
            <br> 
            {{ hero[obj.keys(hero)[0]].title }} - This line also does not work
  `
})
export class HeroComponent {
  @Input()
  hero:Hero;

  obj = Object;
}

Alternatively, you can follow Günter's suggestion and use a different method to solve the issue.

Answer 4

The issue with your code is that Object is not accessible in your component.

To resolve this, you can consider the following approach:

@Component({
  selector: 'hero-component',
  template: `
            {{hero | json }} - This line works and displays the Firebase JSON response below 
            <br>
            {{ obj.keys(hero)[0] }} - This line does not work
            <br> 
            {{ hero[obj.keys(hero)[0]].title }} - This line also does not work
  `
})
export class HeroComponent {
  @Input()
  hero:Hero;

  obj = Object;
}

Alternatively, you can follow Günter's suggestion and use a different method to solve the issue.

Exploring TypeScript Object Properties in Angular 2

Answer №1

Answer №2

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