google.fastbuttons.js

(function() {
  /** 
   * From: http://code.this.com/mobile/articles/fast_buttons.html
   * Also see: http://stackoverflow.com/questions/6300136/trying-to-implement-googles-fast-button 
   */
   
  /** For IE8 and earlier compatibility: https://developer.mozilla.org/en/DOM/element.addEventListener */
  function addListener(el, type, listener, useCapture) {
    if (el.addEventListener) { 
      el.addEventListener(type, listener, useCapture);
      return { 
        destroy: function() { el.removeEventListener(type, listener, useCapture); } 
      };
    } else {      
      // see: http://stackoverflow.com/questions/5198845/javascript-this-losing-context-in-ie
      var handler = function(e) { listener.handleEvent(window.event, listener); }
      el.attachEvent('on' + type, handler);
      
      return { 
        destroy: function() { el.detachEvent('on' + type, handler); }
      };
    }   
  }
  
  var isTouch = "ontouchstart" in window;

  /* Construct the FastButton with a reference to the element and click handler. */
  this.FastButton = function(element, handler, useCapture) {
    // collect functions to call to cleanup events 
    this.events = [];
    this.touchEvents = [];
    this.element = element;
    this.handler = handler;
    this.useCapture = useCapture;
    if (isTouch) 
      this.events.push(addListener(element, 'touchstart', this, this.useCapture));    
    this.events.push(addListener(element, 'click', this, this.useCapture));
  };
  
  /* Remove event handling when no longer needed for this button */
  this.FastButton.prototype.destroy = function() {
    for (i = this.events.length - 1; i >= 0; i -= 1)
      this.events[i].destroy();    
    this.events = this.touchEvents = this.element = this.handler = this.fastButton = null;
  };
  
  /* acts as an event dispatcher */
  this.FastButton.prototype.handleEvent = function(event) {
    switch (event.type) {
      case 'touchstart': this.onTouchStart(event); break;
      case 'touchmove': this.onTouchMove(event); break;
      case 'touchend': this.onClick(event); break;
      case 'click': this.onClick(event); break;
    }
  };
  
  /* Save a reference to the touchstart coordinate and start listening to touchmove and
   touchend events. Calling stopPropagation guarantees that other behaviors don’t get a
   chance to handle the same click event. This is executed at the beginning of touch. */
  this.FastButton.prototype.onTouchStart = function(event) {
    event.stopPropagation ? event.stopPropagation() : (event.cancelBubble=true);
    this.touchEvents.push(addListener(this.element, 'touchend', this, this.useCapture));
    this.touchEvents.push(addListener(document.body, 'touchmove', this, this.useCapture));
    this.startX = event.touches[0].clientX;
    this.startY = event.touches[0].clientY;
  };
  
  /* When /if touchmove event is invoked, check if the user has dragged past the threshold of 10px. */
  this.FastButton.prototype.onTouchMove = function(event) {
    if (Math.abs(event.touches[0].clientX - this.startX) > 10 || Math.abs(event.touches[0].clientY - this.startY) > 10) {
      this.reset(); //if he did, then cancel the touch event
    }
  };
  
  /* Invoke the actual click handler and prevent ghost clicks if this was a touchend event. */
  this.FastButton.prototype.onClick = function(event) {
    event.stopPropagation ? event.stopPropagation() : (event.cancelBubble=true);
    this.reset();
    // Use .call to call the method so that we have the correct "this": https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call
    var result = this.handler.call(this.element, event);
    if (event.type == 'touchend') 
      clickbuster.preventGhostClick(this.startX, this.startY);    
    return result;
  };
  
  this.FastButton.prototype.reset = function() {
    for (i = this.touchEvents.length - 1; i >= 0; i -= 1) 
      this.touchEvents[i].destroy();    
    this.touchEvents = [];
  };
  
  this.clickbuster = function() {}
  
  /* Call preventGhostClick to bust all click events that happen within 25px of
   the provided x, y coordinates in the next 2.5s. */
  this.clickbuster.preventGhostClick = function(x, y) {
    clickbuster.coordinates.push(x, y);
    window.setTimeout(clickbuster.pop, 2500);
  };
  
  this.clickbuster.pop = function() {
    clickbuster.coordinates.splice(0, 2);
  };
  
  /* If we catch a click event inside the given radius and time threshold then we call
   stopPropagation and preventDefault. Calling preventDefault will stop links
   from being activated. */
  this.clickbuster.onClick = function(event) {
    for (var i = 0; i < clickbuster.coordinates.length; i += 2) {
      var x = clickbuster.coordinates[i];
      var y = clickbuster.coordinates[i + 1];
      if (Math.abs(event.clientX - x) < 25 && Math.abs(event.clientY - y) < 25) {
        event.stopPropagation ? event.stopPropagation() : (event.cancelBubble=true);
        event.preventDefault ? event.preventDefault() : (event.returnValue=false);
      }
    }
  };
    
  if (isTouch) {
    // Don't need to use our custom addListener function since we only bust clicks on touch devices
    document.addEventListener('click', clickbuster.onClick, true);
    clickbuster.coordinates = [];
  }
})(this);