Add items and removing all option of dropdown box in javascript

How to add items in dropdown using JavaScript

<script type="text/javascript">

    function AddItem(Text,Value)

    {

        // Create an Option object       

        var opt = document.createElement("option");

      // Add an Option object to Drop Down/List Box

        document.getElementById("DropDownList").options.add(opt);

        // Assign text and value to Option object

        opt.text = Text;

        opt.value = Value;

    }

<script />

Removing all option of dropdown box in JavaScript

document.getElementById('id').options.length = 0;