The MouseEvent.region read-only property returns the id of the canvas hit region affected by the event. If no hit region is affected, null is returned.
Syntax
var hitRegion = instanceOfMouseEvent.region
Return value
A DOMString representing the id of the hit region.
Example
<canvas id="canvas"></canvas>
<script>
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(70, 80, 10, 0, 2 * Math.PI, false);
ctx.fill();
ctx.addHitRegion({id: "circle"});
canvas.addEventListener("mousemove", function(event){
  if(event.region) {
    console.log("hit region: " + event.region);
  }
});
</script>
Specifications
| Specification | Status | Comment | 
|---|---|---|
| WHATWG HTML Living Standard The definition of 'MouseEvent.region' in that specification. | Living Standard | Initial definition | 
Browser compatibility
| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari | 
|---|---|---|---|---|---|
| Basic support | (Yes)[1] | 30 (30)[2] | Not supported | Not supported | Not supported | 
| Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile | 
|---|---|---|---|---|---|---|
| Basic support | Not supported | Not supported | 30.0 (30) | Not supported | Not supported | Not supported | 
[1] This feature is behind a feature flag. Set the flag ExperimentalCanvasFeatures to true to enable it.
[2] This feature is behind a feature preference setting. In about:config, set canvas.hitregions.enabled to true.