code: function inputHandler(manager, eventType, input) {
          var pointersLen = input.pointers.length;
          var changedPointersLen = input.changedPointers.length;
          var isFirst = eventType & INPUT_START && pointersLen - changedPointersLen === 0;
          var isFinal = eventType & (INPUT_END | INPUT_CANCEL) && pointersLen - changedPointersLen === 0;
  
          input.isFirst = !!isFirst;
          input.isFinal = !!isFinal;
  
          if (isFirst) {
              manager.session = {};
          }
  
          // source event is the normalized value of the domEvents
          // like 'touchstart, mouseup, pointerdown'
          input.eventType = eventType;
  
          // compute scale, rotation etc
          computeInputData(manager, input);
  
          // emit secret event
          manager.emit('hammer.input', input);
  
          manager.recognize(input);
          manager.session.prevInput = input;
      }
docs: handle input events
  @param {Manager} manager
  @param {String} eventType
  @param {Object} input