Untitled

if (!e) var e = window.event; // Internet Explorer

if (!e) e = window.event; // Internet Explorer

<html>
<head>
    <title>Mouse Coordinates</title>
    <script type="text/javascript">
        function getCoords(e) {
            var x = 0; // x and y positions
            var y = 0;
            if (!e) var e = window.event; // Internet Explorer
            if (e.pageX || e.pageY) { // Firefox
                x = e.pageX;
                y = e.pageY;
            }
            else if (e.clientX || e.clientY) {
                x = e.clientX + document.body.scrollLeft
              + document.documentElement.scrollLeft;
                y = e.clientY + document.body.scrollTop
                + document.documentElement.scrollTop;
            }
            // x and y contain the mouse position
            // relative to the document
            alert(x + ", " + y);
        }
    </script>
    </head>
        <body>
            <div style="background-color: aqua; position: absolute; top: 50px"
                onmouseover="return getCoords(event);">
                <h1>Mouse positions are relative to the document, not the
<div> container</h1>
            </div>
        </body>
</html>

function getCoords(e) {
     e = e || window.event;
     ...
 }

x = 12;    // using the variable "before" it is declared works
var x = x + 1;