How often does a browser poll for mouse location?

Question

var mouseTrack = (function() {
        document.onmousemove = handleMouseMove;
        function handleMouseMove(event) {
            var dot, eventDoc, doc, body, pageX, pageY;

            event = event || window.event; // IE-ism

            // If pageX/Y aren't available and clientX/Y are,
            // calculate pageX/Y - logic taken from jQuery.
            // (This is to support old IE)
            if (event.pageX == null && event.clientX != null) {
                eventDoc = (event.target && event.target.ownerDocument) || document;
                doc = eventDoc.documentElement;
                body = eventDoc.body;

                event.pageX = event.clientX +
                  (doc && doc.scrollLeft || body && body.scrollLeft || 0) -
                  (doc && doc.clientLeft || body && body.clientLeft || 0);
                event.pageY = event.clientY +
                  (doc && doc.scrollTop  || body && body.scrollTop  || 0) -
                  (doc && doc.clientTop  || body && body.clientTop  || 0 );
            }

            console.log(event.pageX + ', ' + event.pageY);
            // document.body.innerHTML += '<div style="position:absolute;width:3px;height:3px;background:red;right:'+(window.innerWidth-event.pageX)+'px;top:'+event.pageY+'px;"></div>'
        }
    });
    mouseTrack();

(try this in your browser :) )

If you race the mouse on high sensitivity across the page, you'll only get a coordinate set of like 10-20. If you do it slowly, you'll accumulate hundreds or thousands of points.

How often does a browser (let's say, Chrome) poll for mouse location to fire the mousemove event and even better, where is the source I can look at for this?

Answer 1

It is not the browser that is causing this effect. The browser does not poll the mouse position at all, actually.

It is the scripting engines implementation that takes a certain execution time for each command, thus is only able to compare positions every so many microseconds. If a change is detected an event is raised.

It is impossible to name a specific time here in my eyes, since obviously the execution time of single commands depends on the specific hardware and load of the system you test on.