抖动函数

//抖动函数， 对象，频率，属性（上下，左右）
function shake(obj,rate,attr){
    var arr = [];
    var timer = null;
    var num = 0;
    var pos = parseInt(getStyle(obj,attr));
    
    for (var i=0; i<rate; i-=2) {
        arr.push(i,-i);
    }
    arr.push(0);
    clearInterval(timer);
    obj.timer = setInterval(function(){
        obj.style[attr] = pos + arr[num] + ‘px‘;
        num++;
        if (num == arr.length) {
            clearInterval(obj.timer);
        }
        endFn && endFn();
        
    },50);
}