JavaScript Tutorial/Document/onmouseup
document.onmouseup
The onMouseUp event handler specifies what should happen when the mouse button is pressed and then released within the Document object.
<html>
<head>
<script language="JavaScript1.2">
<!--
document.onmouseup = myMouseUpHandler;
function myMouseUpHandler(){
alert("A mouse up event took place within the document!");
}
-->
</script>
</head>
<body>
press the mouse button and then release it
</body>
</html>