hammerjs/src/gestures/tap.js

A javascript library for multi-touch gestures

/**
 * Tap/DoubleTap
 * Quick touch at a place or double at the same place
 * @events  tap, doubletap
 */
Hammer.gestures.Tap = {
  name    : 'tap',
  index   : 100,
  defaults: {
    tap_max_touchtime : 250,
    tap_max_distance  : 10,
    tap_always        : true,
    doubletap_distance: 20,
    doubletap_interval: 300
  },

  has_moved: false,

  handler : function tapGesture(ev, inst) {
    var prev, since_prev, did_doubletap;

    // reset moved state
    if(ev.eventType == EVENT_START) {
      this.has_moved = false;
    }

    // Track the distance we've moved. If it's above the max ONCE, remember that (fixes #406).
    else if(ev.eventType == EVENT_MOVE && !this.moved) {
      this.has_moved = (ev.distance > inst.options.tap_max_distance);
    }

    else if(ev.eventType == EVENT_END &&
        ev.srcEvent.type != 'touchcancel' &&
        ev.deltaTime < inst.options.tap_max_touchtime && !this.has_moved) {

      // previous gesture, for the double tap since these are two different gesture detections
      prev = Detection.previous;
      since_prev = prev && prev.lastEvent && ev.timeStamp - prev.lastEvent.timeStamp;
      did_doubletap = false;

      // check if double tap
      if(prev && prev.name == 'tap' &&
          (since_prev && since_prev < inst.options.doubletap_interval) &&
          ev.distance < inst.options.doubletap_distance) {
        inst.trigger('doubletap', ev);
        did_doubletap = true;
      }

      // do a single tap
      if(!did_doubletap || inst.options.tap_always) {
        Detection.current.name = 'tap';
        inst.trigger(Detection.current.name, ev);
      }
    }
  }
};