js实现缓动效果实例代码

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');