title: Adding an item to interface array list in Typescript
body: <p>I have an interface with name SelectItem  created automatically by primeNG like below. And i want to create an instance and add my select item array. If the SelectItem is class instead of interface, the code will be work. But now, giving an error. <strong>Please don't advice that change the type of SelectItem from interface to "class"</strong>. I can't change because it is component of primeNG. How can i achieve this?</p>
  
  <p>selectitem.ts</p>
  
  <pre><code>export interface SelectItem {
      label?: string;
      value: any;
      styleClass?: string;
      icon?: string;
      title?: string;
      disabled?: boolean;
  }
  </code></pre>
  
  <p>my method</p>
  
  <pre><code>  addUnselectedItem(selectItemList: SelectItem[]) {
      let selectItem = new SelectItem(); //this row giving error
      selectItem.value = "";
      selectItem.label = "Please Select";
  
      selectItemList.push(selectItem);
    }
  </code></pre>