Detect mousemove when over an iframe?

Question

I have an iframe that takes up the entire window (100% wide, 100% high), and I need the main window to be able to detect when the mouse has been moved.

Already tried

Answer 1

Iframes capture mouse events, but you can transfer the events to the parent scope if the cross-domain policy is satisfied. Here's how:

// This example assumes execution from the parent of the the iframe

function bubbleIframeMouseMove(iframe){
    // Save any previous onmousemove handler
    var existingOnMouseMove = iframe.contentWindow.onmousemove;

    // Attach a new onmousemove listener
    iframe.contentWindow.onmousemove = function(e){
        // Fire any existing onmousemove listener 
        if(existingOnMouseMove) existingOnMouseMove(e);

        // Create a new event for the this window
        var evt = document.createEvent("MouseEvents");

        // We'll need this to offset the mouse move appropriately
        var boundingClientRect = iframe.getBoundingClientRect();

        // Initialize the event, copying exiting event values
        // for the most part
        evt.initMouseEvent( 
            "mousemove", 
            true, // bubbles
            false, // not cancelable 
            window,
            e.detail,
            e.screenX,
            e.screenY, 
            e.clientX + boundingClientRect.left, 
            e.clientY + boundingClientRect.top, 
            e.ctrlKey, 
            e.altKey,
            e.shiftKey, 
            e.metaKey,
            e.button, 
            null // no related element
        );

        // Dispatch the mousemove event on the iframe element
        iframe.dispatchEvent(evt);
    };
}

// Get the iframe element we want to track mouse movements on
var myIframe = document.getElementById("myIframe");

// Run it through the function to setup bubbling
bubbleIframeMouseMove(myIframe);

You can now listen for mousemove on the iframe element or any of its parent elements -- the event will bubble up as you would expect.

This is compatible with modern browsers. If you need it to work with IE8 and below, you'll need to use the IE-specific replacements of createEvent, initMouseEvent, and dispatchEvent.