Window.clipboarddata can be used to copy and paste, its getData method can be used to read data, and setData method can be used to setData

 <script language="javascript">
function readTxt()
{
alert(window.clipboardData.getData("text"));
}
function setTxt()
{
var t=document.getElementById("txt");
t.select();
window.clipboardData.setData('text',t.createTextRange().text);
}
</script>
<input name="txt" value=" test ">
<input type="button" value=" copy " onclick="setTxt()">
<input type="button" value=" read " onclick="readTxt()">