title: Angular2 FormBuilder: Using 'this' in a custom validator
body: <p>I'm developing a form using Angular2's FormBuilder with custom validation. 
  Problem: In customValidator I'm using <code>this</code> to access the local object <code>data</code>. I'm getting a <code>undefined</code> error when the validation is executed. </p>
  
  <p>It looks like the customValidator is executed in a different object and therefore changing the <code>this</code> reference</p>
  
  <p><strong>Question:</strong> How can I pass a reference of <code>this</code> to the customValidator?</p>
  
  <pre><code>export class Ast {
      public data:any;
      public myForm:FormGroup;
  
      constructor(private _fb:FormBuilder) {
          this.data = {foo: "bar"};
      }
  
      customValidator(c: FormControl) {
          if (this.data.foo == "bar") { // This line crashes
              // DO something
          }
      }
  
     ngOnInit() {
         this.myForm = this._fb.group({
             some_field: ['', [&lt;any&gt;Validators.required], this.customValidator]
         })
     }
  }
  </code></pre>