前端优化-滚轮事件

1.滚轮相关事件

事件类型	事件对象	是否标准化	兼容性
mousewheel	MouseWheelEvent	非标准化	只有Firefox不支持
DOMMouseScroll	MouseScrollEvent	非标准化	只有Firefox支持
wheel	WheelEvent	DOM Level 3	Firefox 17+/ie9+

wheel事件详细内容：wheel事件

2.通用滚轮事件（wheel）

浏览器类型	evt.wheelDelta	evt.detail
Safari v5/Win7	120	0
Safari v5/OS X	120	0
Safari v7/OS X	12	0
Chrome v11/Win7	120	0
Chrome v37/Win7	120	0
Chrome v11/OS X	3(!)	0(possibly wrong)
Chrome v37/OS X	120	0
IE9/Win7	120	undefined
Opera v11/OS X	40	-1
Opera v24/OS X	120	0
Opera v11/Win7	120	-3
Firefox v4/Win7	undefined	-3
Firefox v4/OS X	undefined	-1
Firefox v30/OS X	undefined	-1

'use strict';

var UserAgent_DEPRECATED = require('UserAgent_DEPRECATED');
var isEventSupported = require('isEventSupported');


// Reasonable defaults
var PIXEL_STEP  = 10;
var LINE_HEIGHT = 40;
var PAGE_HEIGHT = 800;

function normalizeWheel(event)  {
	var sX = 0, sY = 0,       // spinX, spinY
  		pX = 0, pY = 0;       // pixelX, pixelY

	// Legacy
	if ('detail'      in event) { sY = event.detail; }
 	if ('wheelDelta'  in event) { sY = -event.wheelDelta / 120; }
	if ('wheelDeltaY' in event) { sY = -event.wheelDeltaY / 120; }
	if ('wheelDeltaX' in event) { sX = -event.wheelDeltaX / 120; }

	// side scrolling on FF with DOMMouseScroll
	if ( 'axis' in event && event.axis === event.HORIZONTAL_AXIS ) {
		sX = sY;
		sY = 0;
	}

	pX = sX * PIXEL_STEP;
	pY = sY * PIXEL_STEP;

	if ('deltaY' in event) { pY = event.deltaY; }
	if ('deltaX' in event) { pX = event.deltaX; }

	if ((pX || pY) && event.deltaMode) {
		if (event.deltaMode == 1) {          // delta in LINE units
  			pX *= LINE_HEIGHT;
  			pY *= LINE_HEIGHT;
		} else {                             // delta in PAGE units
  			pX *= PAGE_HEIGHT;
  			pY *= PAGE_HEIGHT;
		}
	}

	// Fall-back if spin cannot be determined
	if (pX && !sX) { sX = (pX < 1) ? -1 : 1; }
	if (pY && !sY) { sY = (pY < 1) ? -1 : 1; }

	return { spinX  : sX,
       		 spinY  : sY,
       		 pixelX : pX,
       		 pixelY : pY };
}

/*spinX + spinY标准化的最佳组合。 它支持旧的DOMMouseScroll for Firefox，因为FF不包含带有'wheel'事件的wheelDelta，因此无法确定旋转速度。*/
normalizeWheel.getEventType = function() /*string*/ {
	return (UserAgent_DEPRECATED.firefox())
       	? 'DOMMouseScroll'
       	: (isEventSupported('wheel'))
           	? 'wheel'
           	: 'mousewheel';
};

module.exports = normalizeWheel;