title: Angular 6 : Get one array from other
body: <p>I have array of  IVisitView where </p>
  
  <pre><code>export interface IVisitView {
    visitDate?: Moment;
    clientName?: string;
  }
  
  export class VisitView implements IVisitView {
    constructor(
      public visitDate?: Moment,
      public clientName?: string,
    ) {}
  }
  </code></pre>
  
  <p>How to get a new array with visitDate of String type instead of Moment?</p>