ngClick.js

'use strict';

/**
 * @ngdoc directive
 * @name ngMobile.directive:ngClick
 *
 * @description
 * A more powerful replacement for the default ngClick designed to be used on touchscreen
 * devices. Most mobile browsers wait about 300ms after a tap-and-release before sending
 * the click event. This version handles them immediately, and then prevents the
 * following click event from propagating.
 *
 * This directive can fall back to using an ordinary click event, and so works on desktop
 * browsers as well as mobile.
 *
 * This directive also sets the CSS class `ng-click-active` while the element is being held
 * down (by a mouse click or touch) so you can restyle the depressed element if you wish.
 *
 * @element ANY
 * @param {expression} ngClick {@link guide/expression Expression} to evaluate
 * upon tap. (Event object is available as `$event`)
 *
 * @example
    <doc:example>
      <doc:source>
        <button ng-click="count = count + 1" ng-init="count=0">
          Increment
        </button>
        count: {{ count }}
      </doc:source>
    </doc:example>
 */

ngMobile.config(['$provide', function($provide) {
  $provide.decorator('ngClickDirective', ['$delegate', function($delegate) {
    // drop the default ngClick directive
    $delegate.shift();
    return $delegate;
  }]);
}]);

ngMobile.directive('ngClick', ['$parse', '$timeout', '$rootElement',
    function($parse, $timeout, $rootElement) {
  var TAP_DURATION = 750; // Shorter than 750ms is a tap, longer is a taphold or drag.
  var MOVE_TOLERANCE = 12; // 12px seems to work in most mobile browsers.
  var PREVENT_DURATION = 2500; // 2.5 seconds maximum from preventGhostClick call to click
  var CLICKBUSTER_THRESHOLD = 25; // 25 pixels in any dimension is the limit for busting clicks.

  var ACTIVE_CLASS_NAME = 'ng-click-active';
  var lastPreventedTime;
  var touchCoordinates;


  // TAP EVENTS AND GHOST CLICKS
  //
  // Why tap events?
  // Mobile browsers detect a tap, then wait a moment (usually ~300ms) to see if you're
  // double-tapping, and then fire a click event.
  //
  // This delay sucks and makes mobile apps feel unresponsive.
  // So we detect touchstart, touchmove, touchcancel and touchend ourselves and determine when
  // the user has tapped on something.
  //
  // What happens when the browser then generates a click event?
  // The browser, of course, also detects the tap and fires a click after a delay. This results in
  // tapping/clicking twice. So we do "clickbusting" to prevent it.
  //
  // How does it work?
  // We attach global touchstart and click handlers, that run during the capture (early) phase.
  // So the sequence for a tap is:
  // - global touchstart: Sets an "allowable region" at the point touched.
  // - element's touchstart: Starts a touch
  // (- touchmove or touchcancel ends the touch, no click follows)
  // - element's touchend: Determines if the tap is valid (didn't move too far away, didn't hold
  //   too long) and fires the user's tap handler. The touchend also calls preventGhostClick().
  // - preventGhostClick() removes the allowable region the global touchstart created.
  // - The browser generates a click event.
  // - The global click handler catches the click, and checks whether it was in an allowable region.
  //     - If preventGhostClick was called, the region will have been removed, the click is busted.
  //     - If the region is still there, the click proceeds normally. Therefore clicks on links and
  //       other elements without ngTap on them work normally.
  //
  // This is an ugly, terrible hack!
  // Yeah, tell me about it. The alternatives are using the slow click events, or making our users
  // deal with the ghost clicks, so I consider this the least of evils. Fortunately Angular
  // encapsulates this ugly logic away from the user.
  //
  // Why not just put click handlers on the element?
  // We do that too, just to be sure. The problem is that the tap event might have caused the DOM
  // to change, so that the click fires in the same position but something else is there now. So
  // the handlers are global and care only about coordinates and not elements.

  // Checks if the coordinates are close enough to be within the region.
  function hit(x1, y1, x2, y2) {
    return Math.abs(x1 - x2) < CLICKBUSTER_THRESHOLD && Math.abs(y1 - y2) < CLICKBUSTER_THRESHOLD;
  }

  // Checks a list of allowable regions against a click location.
  // Returns true if the click should be allowed.
  // Splices out the allowable region from the list after it has been used.
  function checkAllowableRegions(touchCoordinates, x, y) {
    for (var i = 0; i < touchCoordinates.length; i += 2) {
      if (hit(touchCoordinates[i], touchCoordinates[i+1], x, y)) {
        touchCoordinates.splice(i, i + 2);
        return true; // allowable region
      }
    }
    return false; // No allowable region; bust it.
  }

  // Global click handler that prevents the click if it's in a bustable zone and preventGhostClick
  // was called recently.
  function onClick(event) {
    if (Date.now() - lastPreventedTime > PREVENT_DURATION) {
      return; // Too old.
    }

    // retrieve original event if it is wrapped by jquery
    // the original event will have an array of touches
    event = event.originalEvent || event;
    
    var touches = event.touches && event.touches.length ? event.touches : [event];
    var x = touches[0].clientX;
    var y = touches[0].clientY;
    // Work around desktop Webkit quirk where clicking a label will fire two clicks (on the label
    // and on the input element). Depending on the exact browser, this second click we don't want
    // to bust has either (0,0) or negative coordinates.
    if (x < 1 && y < 1) {
      return; // offscreen
    }

    // Look for an allowable region containing this click.
    // If we find one, that means it was created by touchstart and not removed by
    // preventGhostClick, so we don't bust it.
    if (checkAllowableRegions(touchCoordinates, x, y)) {
      return;
    }

    // If we didn't find an allowable region, bust the click.
    event.stopPropagation();
    event.preventDefault();
  }


  // Global touchstart handler that creates an allowable region for a click event.
  // This allowable region can be removed by preventGhostClick if we want to bust it.
  function onTouchStart(event) {
    // retrieve original event which has touches
    event = event.originalEvent || event;

    var touches = event.touches && event.touches.length ? event.touches : [event];
    var x = touches[0].clientX;
    var y = touches[0].clientY;
    touchCoordinates.push(x, y);

    $timeout(function() {
      // Remove the allowable region.
      for (var i = 0; i < touchCoordinates.length; i += 2) {
        if (touchCoordinates[i] == x && touchCoordinates[i+1] == y) {
          touchCoordinates.splice(i, i + 2);
          return;
        }
      }
    }, PREVENT_DURATION, false);
  }

  // On the first call, attaches some event handlers. Then whenever it gets called, it creates a
  // zone around the touchstart where clicks will get busted.
  function preventGhostClick(x, y) {
    if (!touchCoordinates) {
      $rootElement[0].addEventListener('click', onClick, true);
      $rootElement[0].addEventListener('touchstart', onTouchStart, true);
      touchCoordinates = [];
    }

    lastPreventedTime = Date.now();

    checkAllowableRegions(touchCoordinates, x, y);
  }

  // Actual linking function.
  return function(scope, element, attr) {
    var clickHandler = $parse(attr.ngClick),
        tapping = false,
        tapElement,  // Used to blur the element after a tap.
        startTime,   // Used to check if the tap was held too long.
        touchStartX,
        touchStartY;

    function resetState() {
      tapping = false;
      element.removeClass(ACTIVE_CLASS_NAME);
    }

    element.on('touchstart', function(event) {
      tapping = true;
      event = event.originalEvent || event;

      tapElement = event.target ? event.target : event.srcElement; // IE uses srcElement.
      // Hack for Safari, which can target text nodes instead of containers.
      if(tapElement.nodeType == 3) {
        tapElement = tapElement.parentNode;
      }

      element.addClass(ACTIVE_CLASS_NAME);

      startTime = Date.now();

      var touches = event.touches && event.touches.length ? event.touches : [event];
      var e = touches[0].originalEvent || touches[0];
      touchStartX = e.clientX;
      touchStartY = e.clientY;
    });

    element.on('touchmove', function(event) {
      resetState();
    });

    element.on('touchcancel', function(event) {
      resetState();
    });

    element.on('touchend', function(event) {
      var diff = Date.now() - startTime;
      event = event.originalEvent || event;

      var touches = (event.changedTouches && event.changedTouches.length) ? event.changedTouches :
          ((event.touches && event.touches.length) ? event.touches : [event]);
      var e = touches[0].originalEvent || touches[0];
      var x = e.clientX;
      var y = e.clientY;
      var dist = Math.sqrt( Math.pow(x - touchStartX, 2) + Math.pow(y - touchStartY, 2) );

      if (diff < TAP_DURATION && dist < MOVE_TOLERANCE) {
        // Call preventGhostClick so the clickbuster will catch the corresponding click.
        preventGhostClick(x, y);

        // Blur the focused element (the button, probably) before firing the callback.
        // This doesn't work perfectly on Android Chrome, but seems to work elsewhere.
        // I couldn't get anything to work reliably on Android Chrome.
        if (tapElement) {
          tapElement.blur();
        }

        scope.$apply(function() {
          // TODO(braden): This is sending the touchend, not a tap or click. Is that kosher?
          clickHandler(scope, {$event: event});
        });
      }

      resetState();
    });

    // Hack for iOS Safari's benefit. It goes searching for onclick handlers and is liable to click
    // something else nearby.
    element.onclick = function(event) { };

    // Fallback click handler.
    // Busted clicks don't get this far, and adding this handler allows ng-tap to be used on
    // desktop as well, to allow more portable sites.
    element.on('click', function(event) {
      scope.$apply(function() {
        clickHandler(scope, {$event: event});
      });
    });

    element.on('mousedown', function(event) {
      element.addClass(ACTIVE_CLASS_NAME);
    });

    element.on('mousemove mouseup', function(event) {
      element.removeClass(ACTIVE_CLASS_NAME);
    });

  };
}]);