How to copy text to clipboard in javascript

If the user want to copy some content ,he have to select some content then right click ,then click copy.if u want in ur appplication that there will be a control onclick of which the content of controls for example textbox will copy to click board,then call a javascript function onclick that button

< input type="button" value="copy" onclick="CopyToClipboard();">

function CopyToClipboard()

{
var textboxVal = document.getElementById("txtCopy").value; //txtText id of a textbox
if( window.clipboardData && clipboardData.setData )
{
clipboardData.setData("Text", textboxVal);
}
else
{
alert("works only in IE4+");
}
}