 <p>I think it's actually not need because <strong>WidgetsModule</strong> is same as <strong>FormsModule</strong> (@angular/forms). WidgetsModule is user-defined module and FormsModule provided by angular. That's the only difference. Both of this module are used for doing some functionality. </p> <p>So just think about <em>how we can declare <strong>FormsModule</strong> once and use it in all other module</em>, if you understood that then the problem is solved.</p> <p>Just vist the following link <a href="http://stackoverflow.com/questions/39756178/one-single-ngmodule-versus-multiples-ones-with-angular-2/39756821">One single NgModule versus multiples ones with Angular 2</a></p>