Copying value from one input field to another input field
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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,

      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?