Angular

What it does

Configures a view query.

How to use

import {AfterViewInit, Component, Directive, ViewChild} from '@angular/core';

@Directive({selector: 'child-directive'})
class ChildDirective {
}

@Component({selector: 'someCmp', templateUrl: 'someCmp.html'})
class SomeCmp implements AfterViewInit {
  @ViewChild(ChildDirective) child: ChildDirective;

  ngAfterViewInit() {
    // child is set
  }
}

Description

You can use ViewChild to get the first element or the directive matching the selector from the view DOM. If the view DOM changes, and a new child matches the selector, the property will be updated.

View queries are set before the ngAfterViewInit callback is called.

Metadata Properties:

selector - the directive type or the name used for querying.
read - read a different token from the queried elements.

import {Component, Directive, Input, ViewChild} from '@angular/core';

@Directive({selector: 'pane'})
export class Pane {
  @Input() id: string;
}

@Component({
  selector: 'example-app',
  template: `
    <pane id="1" *ngIf="shouldShow"></pane>
    <pane id="2" *ngIf="!shouldShow"></pane>

    <button (click)="toggle()">Toggle</button>

    <div>Selected: {{selectedPane}}</div> 
  `,
})
export class ViewChildComp {
  @ViewChild(Pane)
  set pane(v: Pane) {
    setTimeout(() => { this.selectedPane = v.id; }, 0);
  }
  selectedPane: string = '';
  shouldShow = true;
  toggle() { this.shouldShow = !this.shouldShow; }
}

npm package: @angular/core

exported from @angular/core/index defined in @angular/core/src/metadata/di.ts