(function(){
    window.requestAnimationFrame = window.requestAnimationFrame||window.webkitRequestAnimationFrame||window.mozRequestAnimationFrame;
    window.cancelAnimationFrame = window.cancelAnimationFrame|| window.webkitCancelAnimationFrame || window.mozCancelAnimationFrame||window.cancelRequestAnimationFrame||window.webkitCancelRequestAnimationFrame||window.mozCancelRequestAnimationFrame; 
    if(!requestAnimationFrame){
        var lastTime = Date.now();
        window.requestAnimationFrame = function(callback){
            var id;
            var nowTime = Date.now();
            var delay = Math.max(16.7-(nowTime-lastTime),0);
            id = setTimeout(callback,delay);
            lastTime = nowTime + delay;
            return id;
        };
    }
    if(!cancelAnimationFrame){
        window.cancelAnimationFrame = function(index){
            clearTimeout(index);
        };
    }
})();



function transform(el,attr,val){
    if(!el.transform){
        el.transform = {
        };
    }
    if(val === undefined){
        return el.transform[attr];
    }
    el.transform[attr] = val;
    var str = "";
    for(var s in el.transform){
        switch(s){
            case "rotate":
            case "rotateX":
            case "rotateY":
            case "rotateZ":
            case "skewX":
            case "skewY":
                str += s +"("+el.transform[s]+"deg) ";
                break;
            case "scale":
            case "scaleX":
            case "scaleY":
                str += s +"("+el.transform[s]+") ";
                break;
            case "translateX":
            case "translateY":
            case "translateZ":
                str += s +"("+el.transform[s]+"px) ";
                break;    
        }
    }
    el.style.WebkitTransform = el.style.transform = str;
}

function css(el,attr,val){
    var transformAttr = ["rotate","rotateX","rotateY","rotateZ","skewX","skewY","scale","scaleX","scaleY","translateX","translateY","translateZ"];
    for(var i = 0; i < transformAttr.length; i++){
        if(attr == transformAttr[i]){
            return transform(el,attr,val);
        }
    }
    if(val === undefined){
        val = getComputedStyle(el)[attr];
        console.log(val);
        val = parseFloat(val);
        return val;
    }
    if(attr == "opacity"){
        el.style[attr] = val;
    } else {
        el.style[attr] = val + "px";
    }
}    

function mTween(init){
    var t = 0;
    var b = {};
    var c = {};    
    var d = Math.ceil(init.time/16.7);
    cancelAnimationFrame(init.el.timer);
    for(var s in init.target) {
        b[s] = css(init.el,s);
        c[s] = init.target[s] - b[s];
    }
    init.el.timer = requestAnimationFrame(move);
    function move(){
        if(t > d){
            cancelAnimationFrame(init.el.timer);
            init.callBack&&init.callBack.call(init.el);
        } else {
            t++;
            for(var s in init.target){
                var val = Tween[init.type](t,b[s],c[s],d);
                css(init.el,s,val);
            }
            init.callIn&&init.callIn.call(init.el);
            init.el.timer = requestAnimationFrame(move);
        }
    }
}

var box = document.querySelector(‘#box‘);
css(box,"translateX",0);
css(box,"translateY",0);
mTween({
    el: box,
    type: "elasticIn",
    time: 1000,
    target: {
    translateX: 200,
    translateY: 400
  },
  callBack: function(){
    console.log("动画执行完了");
  },
  callIn: function(){
    console.log("动画执行中");    
  }
});