edds/index.html

## index.html
<!doctype html>

<title>Dynamic SVG Mask</title>
<style>
  div {
    width: 800px;
    height: 800px;
    background: #000;
  }
</style>

<div></div>

<script type="text/javascript">
  function Spotlight(el, radius){
    this.x = 0;
    this.y = 0;
    this.radius = radius || 0;

    this.el = el;
    this.el.addEventListener('mousemove', this.move.bind(this), false);
    this.el.addEventListener("touchmove", this.touchMove.bind(this), false);
  }
  Spotlight.prototype = {
    move: function(e){
      this.set({
        x: e.clientX + window.scrollX,
        y: e.clientY + window.scrollY
      });
    },
    touchMove: function(e){
      e.preventDefault();
      var touch = e.targetTouches[0];
      if(touch){
        this.set({
          x: touch.clientX + window.scrollX,
          y: touch.clientY + window.scrollY
        });
      }
    },
    set: function(cords){
      this.x = cords.x;
      this.y = cords.y;

      this.update();
    },
    update: function(){
      this.el.setAttribute('style', '-webkit-mask-image: url("data:image/svg+xml;utf8,'+this.svg()+'");');
    },
    svg: function(){
      var x = this.x,
          y = this.y,
          r = this.radius;

      return "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink'>"
        + "<circle cx='"+x+"' cy='"+y+"' r='"+r+"' style='fill:#000000'/>"
        + "</svg>";
    }

  };
  window.addEventListener('DOMContentLoaded', function(){
    var s = new Spotlight(document.getElementsByTagName('div')[0], 100);
  }, false);

  // Borrowed from MDN bind docs.
  // https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/bind
  if (!Function.prototype.bind) {
    Function.prototype.bind = function (oThis) {
      if (typeof this !== "function") {
        // closest thing possible to the ECMAScript 5 internal IsCallable function
        throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
      }

      var aArgs = Array.prototype.slice.call(arguments, 1),
          fToBind = this,
          fNOP = function () {},
          fBound = function () {
            return fToBind.apply(this instanceof fNOP ? this : oThis || window,
                                 aArgs.concat(Array.prototype.slice.call(arguments)));
          };

      fNOP.prototype = this.prototype;
      fBound.prototype = new fNOP();

      return fBound;
    };
  }
</script>
	<!doctype html>

	<title>Dynamic SVG Mask</title>
	<style>
	div {
	width: 800px;
	height: 800px;
	background: #000;
	}
	</style>

	<div></div>

	<script type="text/javascript">
	function Spotlight(el, radius){
	this.x = 0;
	this.y = 0;
	this.radius = radius \|\| 0;

	this.el = el;
	this.el.addEventListener('mousemove', this.move.bind(this), false);
	this.el.addEventListener("touchmove", this.touchMove.bind(this), false);
	}
	Spotlight.prototype = {
	move: function(e){
	this.set({
	x: e.clientX + window.scrollX,
	y: e.clientY + window.scrollY
	});
	},
	touchMove: function(e){
	e.preventDefault();
	var touch = e.targetTouches[0];
	if(touch){
	this.set({
	x: touch.clientX + window.scrollX,
	y: touch.clientY + window.scrollY
	});
	}
	},
	set: function(cords){
	this.x = cords.x;
	this.y = cords.y;

	this.update();
	},
	update: function(){
	this.el.setAttribute('style', '-webkit-mask-image: url("data:image/svg+xml;utf8,'+this.svg()+'");');
	},
	svg: function(){
	var x = this.x,
	y = this.y,
	r = this.radius;

	return "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink'>"
	+ "<circle cx='"+x+"' cy='"+y+"' r='"+r+"' style='fill:#000000'/>"
	+ "</svg>";
	}

	};
	window.addEventListener('DOMContentLoaded', function(){
	var s = new Spotlight(document.getElementsByTagName('div')[0], 100);
	}, false);

	// Borrowed from MDN bind docs.
	// https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/bind
	if (!Function.prototype.bind) {
	Function.prototype.bind = function (oThis) {
	if (typeof this !== "function") {
	// closest thing possible to the ECMAScript 5 internal IsCallable function
	throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
	}

	var aArgs = Array.prototype.slice.call(arguments, 1),
	fToBind = this,
	fNOP = function () {},
	fBound = function () {
	return fToBind.apply(this instanceof fNOP ? this : oThis \|\| window,
	aArgs.concat(Array.prototype.slice.call(arguments)));
	};

	fNOP.prototype = this.prototype;
	fBound.prototype = new fNOP();

	return fBound;
	};
	}
	</script>