Simple tracking mouse object

track.js

function Track(context) {
  function addEvent(type, fn) {
    // context is scoped in Track object
    context.addEventListener(type, fn, false);
    return addEvent;
  }
  
  function getXY(event) {
    return {
      x: (event.pageX || event.touches[0].pageX) - document.body.scrollLeft,
      y: (event.pageY || event.touches[0].pageY) - document.body.scrollTop,
    }
  }
  
  function down(event) {
    track.down = true;
    var coords = getXY(event);
    track.downX = coords.x;
    track.downY = coords.y;
    track.downTime = +new Date;
  }
  
  function up(event) {
    track.down = false;    
    track.delta = +new Date - track.downTime;
  }
  
  function move(event) {
    var coords = getXY(event);
    track.x = coords.x;
    track.y = coords.y;    
  }
  
  var track = this;
  
  // http://twitter.com/LeaVerou/status/16613276313980928
  context || (context = document);
  
  // hook up event listeners
  addEvent('mousedown', down)('mouseup', up)('touchstart', down)('touchend', up)('mousemove', move)('touchmove', move)('keydown', function (event) {
    track.key[event.which] = true;
  })('keyup', function () {
    track.key[event.which] = false;
  });
}

Track.prototype = {
  key: {}, // note that key tracking isn't perfect yet - probably won't be :(
  x: 0,
  y: 0,
  downTime: 0,
  delta: 0,
  downX: 0,
  downY: 0,
  down: false
};