css3高级运动keyframes

<!DOCTYPE html>
<html >
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script>
            window.onload=function(){
                var arr=[-45,60,-75,90];
                var i=0;
                box.onclick=function(){
                var ready=false;
                i++;
                var oH=document.getElementsByTagName('head')[0];
                var oS=document.createElement('style');
                oH.appendChild(oS);
                  oS.innerHTML=
                    '@keyframes rotate{'+
                    '0%{'+
                    'transform: rotate('+arr[i%4]+'deg);'+
                    '}'+
                    '100%{'+
                    'transform: rotate(-'+arr[i%4]+'deg);'+
                    '}'+
                    '}';
                box.style.animation='1s rotate linear';    
                box.addEventListener('animationend',function(){
                    if(ready)return;
                    ready=true;
                    document.getElementsByTagName('head')[0].removeChild(oS);
                },false);
                console.log(oS.innerHTML);
                };

            };
    </script>
</head>
<body>
    <div ></div>
</body>
</html>