I have a component that has `form` element inside it. This form has an `input[type="number"]` which will be used to adjust an `iframe` element. The problem is, the `iframe` element is inside `@ViewChild`. How do I pass the `[(ng-model)]` on the form input to the `[width]` on the `iframe` inside `@ViewChild`? The code looks something like this:

```
@Component({
  selector: "demo-iframe",
  template: `
  <form (submit)="onSubmit($event)">
    <input type="number" min="0" [(ngModel)]="model.px">px
    <button>update px</button>
  </form>
  <div #placeholder></div>
  `
})

export class DemoIframeCmp {
  @ViewChild("placeholder", { read: ViewContainerRef }) private viewContainerRef: ViewContainerRef;

 constructor (
   private route: ActivatedRoute,
   private router: Router,
   private compiler: Compiler
 ) {
    document.title = "Test iframe";
    this.paramsSub = this.route.params.subscribe((params: IClickDemoParams) => {
      document.title = `Demo iframe ${params.demoId}`;
      this.buildDemo( params.demoId );
    });

    this.setWidth = 800;
   }

  private buildDemo (selector: string) {
    @Component({
      selector: "test-iframe",
      template: `
        <iframe class="iframe-demo" src="http://localhost:3000/${selector}" [width]="px"></iframe>
      `
    })

 }

```