Two way binding in reactive forms

Note: as mentioned by @Clouse24, “Using Reactive Froms with ngModel is deprecated in angular 6 and will be removed in a future version of Angular” (which means that the answer below will no longer be supported in the future). Please read the link to see the reasoning for deprecation and to see what alternatives you will have.

You can use [(ngModel)] with Reactive forms.

template

<form [formGroup]="form">
  <input name="first" formControlName="first" [(ngModel)]="example.first"/>
  <input name="last" formControlName="last" [(ngModel)]="example.last"/>
</form>

component

export class App {
  form: FormGroup;
  example = { first: "", last: "" };

  constructor(builder: FormBuilder) {
    this.form = builder.group({
      first: "",
      last: ""
    });
  }
}

Plunker

This will a completely different directive than the one that would be used without the formControlName. With reactive forms, it will be the FormControlNameDirective. Without the formControlName, the NgModel directive would be used.