I need a javascript function for copying the value of one input field to another input field based on checkbox selection. However i did some javascript code on click,

```
<script>    
function copyTextValue() {
    var text1 = document.getElementById("Name1").value;
    document.getElementById("Name2").value = text1;
    document.getElementById("Name3").value=text1;
}
</script>

<input type="checkbox" name="check1" onclick="copyTextValue();"/>

```

Now i need to delete the copied values in those two boxes on uncheck. I stuck up with this. Any help?