JS实现匀加速与匀减速运动的方法示例

/*
 * 动画帧函数
 *
 * */
 var requestFrame=function(){
 var prefixList=['webkit','moz','ms'];
 var func;
 for(var i=0;i<prefixList.length;i++){
 func=window[prefixList[i]+"RequestAnimationFrame"];
 if(func){
 return function(callback){
 func(callback);
 }
 }
 }
 return function(callback){
 setTimeout(callback,67);
 }
}();
/*
 * 匀加速运动
 *
 * */
function animate_easeIn(element,from,to,duration,callback){
 var time=+new Date;
 var distance=to-from;
 var a=2*distance/(duration*duration); //加速度a=2x/t^2（包含方向）
 var func=function(){
 var time2,offsetDis,durTime;
 time2=+new Date;
 durTime=time2-time; //运动的时间间隔
 offsetDis=Math.ceil(a*durTime*durTime/2);//X=a*t^2/2
 if(duration<durTime){
 element.css('left',to+'px');
 callback();
 }else{
 element.css('left',from+offsetDis+'px');
 requestFrame(func);
 }
 }
 func();
}
/*
 * 匀减速运动
 *
 * */
function animate_easeOut(element,from,to,duration,callback){
 var time=+new Date;
 var distance=Math.abs(to-from);
 var a=2*distance/(duration*duration); //x=a*t^2/2 求出加速度
 var v0=Math.sqrt(distance*2*a); // 根据公式：2as=v^2求出初速度
 var func=function(){
 var time2,offsetDis,durTime,pos;
 time2=+new Date;
 durTime=time2-time;
 offsetDis=Math.ceil(v0*durTime-a*durTime*durTime/2); //根据s=v0*t+1/2*a*t^2求出位移x
 if(duration<durTime){
 element.css('left',to+'px');
 callback();
 }else{
 pos=from>to? from-offsetDis : from+offsetDis;
 element.css('left',pos+'px');
 requestFrame(func);
 }
 }
 func();
}