getstyle性能比较

var Element = {};
Element.getStyles1 = function() {
	var view = document.defaultView;
	var propCache = {};
	var camelRe = /(-[a-z])/gi;
	var camelFn = function(m, a) {
		return a.charAt(1).toUpperCase();
	};
	return view && view.getComputedStyle ? function(el, prop) {
		var v, cs, camel;
		if (prop == 'float') {
			prop = "cssFloat";
		}
		if (v = el.style[prop]) {
			return v;
		}
		if (cs = view.getComputedStyle(el, "")) {
			//if (!(camel = propCache[prop])) {
				//camel = propCache[prop] = prop.replace(camelRe, camelFn);
		//	}
				camel = prop.replace(camelRe, camelFn);
			return cs[camel];
		}
		return null;
	} : function(el, prop) {
		var v, cs, camel;
		if (prop == 'opacity') {
			if (typeof el.style.filter == 'string') {
				var m = el.style.filter.match(/alpha\(opacity=(.*)\)/i);
				if (m) {
					var fv = parseFloat(m[1]);
					if (!isNaN(fv)) {
						return fv ? fv / 100 : 0;
					}
				}
			}
			return 1;
		} else if (prop == 'float') {
			prop = "styleFloat";
		}
		if (!(camel = propCache[prop])) {
			camel = propCache[prop] = prop.replace(camelRe, camelFn);
		}
		if (v = el.style[camel]) {
			return v;
		}
		if (cs = el.currentStyle) {
			return cs[camel];
		}
		return null;
	};

}();
Element.getStyles2  = function(element, style) {
	var camelRe = /(-[a-z])/gi;
	var propCache = {};
	var camelFn = function(m, a) {
		return a.charAt(1).toUpperCase();
	};	
	//if (!(camel = propCache[style])) {
			camel = propCache[style] = style.replace(camelRe, camelFn);
	//	}
	style = style == 'float' ? 'cssFloat' : camel;//style.replace(camelRe, camelFn);;
	var value = element.style[style];
	if (!value || value == 'auto') {
		if(document.defaultView)
		var css = document.defaultView.getComputedStyle(element, null);
		value = css ? css[style] : null;
	}
	if (style == 'opacity')
		return value ? parseFloat(value) : 1.0;
	return value == 'auto' ? null : value;
};



var s = ['width', 'heigth', 'opacity', 'float', 'margin', 'border',
		'background', 'top', 'button','padding-left','padding-right','margin-bottom','border-bottom-width','border-right-width'];
var now = new Date().getTime();
for (var i = 0;i < 10000; i++) {
	var m =parseInt(Math.random()*(s.length-1))+1; 	
	var el=document.getElementById('test1');
	Element.getStyles1(el, s[m]);
}
var now1 = new Date().getTime();
alert(now1 - now);

var now = new Date().getTime();
for (var i = 0;i < 10000; i++) {
	var m =parseInt(Math.random()*(s.length-1))+1;
	 Element.getStyles2 (document.getElementById('test1'), s[m]);
}
var now1 = new Date().getTime();
alert(now1 - now);

 在分析Ext，觉得ext,yui（类似style1的实现）要不要这样做，于是做了一个性能的测试

在IE中 style1:420-440之间，style2:'453-470之间

在FF中，style1:953-970之间，style2:1266-1287之间

加上came缓存的性能提升在0-20之间。

 

先不用去说prototype，mootools的类似的getstyle2的实现上有点问题。而且性能还是差很多，要慢五分之一。