fade方法

function fadeOut(steps){  
    doFade.call(this,steps/10,1,false);   
};  
function fadeIn(steps){  
    doFade.call(this,steps/10,0,true);    
};  
function doFade(steps,value,action,fn){  
    var ie=undefined!==window.ActiveXObject,calls=arguments.callee,t=this,step;
		value+=(action?1:-1)/steps,(action?value>1: value<0) && (value=action?1:0),ie===true ? t.style.filter='alpha(opacity='+value*100+')' : t.style.opacity=value;
		(action?value<1:value>0) && setTimeout(function(){
			calls.call(t,steps,value,action,fn);			
		},1000/steps);
		(action?value===1:value===0 && 'undefined'!==typeof fn) && ('function'===typeof fn && fn.call(t)); 
}