javascript动画对象支持加速、减速、缓入、缓出的实现代码

调用接口：
复制代码 代码如下:

effect.animate(elem, params, duration, easing, callback);

使用它用不了20行代码就可以做一个产品图片减速淡出、加速淡入的切换效果点击这里查看演示效果
复制代码 代码如下:
//辅助对象，读/写DOM元素属性
var attribute = {
get: function(elem, attr){
var val;
if(elem.currentStyle){
if(attr === "opacity") {
val = elem.filters.alpha[attr];
}else {
val = elem.currentStyle[attr];
}
}
else{
val = getComputedStyle(elem)[attr];
if(attr === "opacity") {
val = 100 * val;
}
}
return val;
},
set: function(elem, attr, val){
if(attr=='opacity'){
elem.style.filter = 'alpha(opacity='+ (val) +')';
elem.style.opacity = (val)/100;
}
else{
elem.style[attr] = val + 'px';
}
}
};

var tween = {
//缓入
easeIn: function (t, b, c, d){
return c * (t/=d) * t + b;
},
//缓出
easeOut: function (t,b,c,d){
return -c * (t/=d) * (t-2) + b;
}
};
//动画对象
var effect = {
animate: function(elem, params, duration, easing, callback){
var dt = new Date().getTime(),
b = 0,
c = 0,
d = duration || 500,
fps = 1000/60;
var changes = [];
for(var attr in params){
b = parseFloat(attribute.get(elem, attr));
c = params[attr] - b;
changes.push({
attr: attr,
b: b,
c: c
});
}
easing = easing || "easeOut";
callback = callback || new Function;
setTimeout(function(){
var t = new Date().getTime() - dt;
var b, c, attr;
for(var i=0; ib = changes[i].b;
c = changes[i].c;
attr = changes[i].attr;
attribute.set(elem, attr, tween[easing](t, b, c, d));
if(d <= t){
attribute.set(elem, attr, params[attr]);
callback();
return;
}
}
setTimeout(arguments.callee, fps);
}, fps);
}
};
//by rentj1@163.com