var tween = {    linear:function(t,b,c,d){        return c*t/d + b;    },    easeIn:function(t,b,c,d){        return c * ( t /= d ) * t + b;    },    strongEaseIn:function(t,b,c,d){        return c * ( t /= d ) * t * t * t * t + b;    },    strongEaseOut:function(t,b,c,d){        return c * ( ( t = t / d -1 ) * t * t * t * t +1 ) + b;    },    sineaseIn:function(t,b,c,d){        return c * ( t /= d ) * t * t + b;        },    sineaseOut:function(t,b,c,d){        return c * ( ( t = t / d -1 ) * t * t *t +1 ) + b;    }};var Animate = function(dom){    this.dom = dom;    this.startTime = 0;    this.startPos = 0;    this.endPos = 0;    this.propertyName = null;    this.easing = null;    this.duration = null;}Animate.prototype.start = function(propertyName,endPos,duration,easing){    this.startTime = +new Date;    this.startPos = this.dom.getBoundingClientRect()[propertyName];    this.propertyName = propertyName;    this.endPos = endPos;    this.duration = duration;    this.easing = tween[easing];    var self = this;    var timeId = setInterval(function(){        if(self.step() === false){            clearInterval(timeId);        }    },19);}Animate.prototype.step = function(){    var t = +new Date;    if(t>=this.startTime + this.duration){        this.update(this.endPos);        return false;    }    var pos = this.easing(t-this.startTime, this.startPos, this.endPos - this.startPos, this.duration);    this.update(pos);}Animate.prototype.update = function(pos){    this.dom.style[this.propertyName] = pos + ‘px‘;}var div = document.getElementById(‘div‘);var animate = new Animate(div);animate.start(‘left‘,500,1000,‘strongEaseOut‘);