game-shell/lib/mousewheel-polyfill.js

Ready-to-go game shell

//Adapted from here: https://developer.mozilla.org/en-US/docs/Web/Reference/Events/wheel?redirectlocale=en-US&redirectslug=DOM%2FMozilla_event_reference%2Fwheel

var prefix = "", _addEventListener, onwheel, support;

// detect event model
if ( window.addEventListener ) {
  _addEventListener = "addEventListener";
} else {
  _addEventListener = "attachEvent";
  prefix = "on";
}

// detect available wheel event
support = "onwheel" in document.createElement("div") ? "wheel" : // Modern browsers support "wheel"
          document.onmousewheel !== undefined ? "mousewheel" : // Webkit and IE support at least "mousewheel"
          "DOMMouseScroll"; // let's assume that remaining browsers are older Firefox

function _addWheelListener( elem, eventName, callback, useCapture ) {
  elem[ _addEventListener ]( prefix + eventName, support == "wheel" ? callback : function( originalEvent ) {
    !originalEvent && ( originalEvent = window.event );

    // create a normalized event object
    var event = {
      // keep a ref to the original event object
      originalEvent: originalEvent,
      target: originalEvent.target || originalEvent.srcElement,
      type: "wheel",
      deltaMode: originalEvent.type == "MozMousePixelScroll" ? 0 : 1,
      deltaX: 0,
      delatZ: 0,
      preventDefault: function() {
        originalEvent.preventDefault ?
          originalEvent.preventDefault() :
          originalEvent.returnValue = false;
      }
    };
    
    // calculate deltaY (and deltaX) according to the event
    if ( support == "mousewheel" ) {
      event.deltaY = - 1/40 * originalEvent.wheelDelta;
      // Webkit also support wheelDeltaX
      originalEvent.wheelDeltaX && ( event.deltaX = - 1/40 * originalEvent.wheelDeltaX );
    } else {
      event.deltaY = originalEvent.detail;
    }

    // it's time to fire the callback
    return callback( event );
  }, useCapture || false );
}

module.exports = function( elem, callback, useCapture ) {
  _addWheelListener( elem, support, callback, useCapture );

  // handle MozMousePixelScroll in older Firefox
  if( support == "DOMMouseScroll" ) {
    _addWheelListener( elem, "MozMousePixelScroll", callback, useCapture );
  }
};