Getting the mouse co-ordinates in JavaScript (all browsers)

We are going to create two functions mouseX(event),  mouseY(event). In each function we do the following

• Get the event triggered
• Find the X or Y co-ordinate of that event

function mouseX(evt) {
evt = (evt) ? evt : ((event) ? event : null);
if (evt.pageX) return evt.pageX;
if (evt.clientX)
return evt.clientX + (document.documentElement.scrollLeft ? document.documentElement.scrollLeft : document.body.scrollLeft);
else return null;
}

function mouseY(evt) {
evt = (evt) ? evt : ((event) ? event : null);
if (evt.pageY) return evt.pageY;
else if (evt.clientY)
return evt.clientY + (document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop);
else return null;