[Angular] ViewChild 'read' option

It is not clear in the Docs about {read: xx} option for @ViewChild.

?

Based on the Source code,@ViewChild as view as Component,ElementRef,TemplateRef.

For example,we have:

<one></one>

  @ViewChild(OneComponent)
  one: OneComponent;

  ngAfterViewInit() {
    console.log(‘after‘,this.one);
  }

Now we read ‘OneComponent‘ as a component,if we want to read it as ElementRef,we can do:

  @ViewChild(OneComponent,{read: ElementRef})
  one: ElementRef;