js抛物线动画

/**
     * js抛物线动画
     * @param  {[object]} origin [起点元素]
     * @param  {[object]} target [目标点元素]
     * @param  {[object]} element [要运动的元素]
     * @param  {[number]} a [抛物线弧度]
     * @param  {[number]} time [动画执行时间]
     * @param  {[function]} callback [抛物线执行完成后回调]
     */
    var parabola = function(config){
        var b = 0,
            INTERVAL = 15,
            timer = null,
            x1,y1,x2,y2,originx,originy,diffx,diffy;

        this.config = config || {};
        // 起点
        this.origin = $(this.config.origin)||null;
        // 终点
        this.target = $(this.config.target)||null;
        // 运动的元素
        this.element = $(this.config.element)||null;
        // 曲线弧度
        this.a = this.config.a || 0.004;
        // 运动时间(ms)
        this.time = this.config.time || 1000;

        this.init = function(){
            x1 = this.origin.offset().left;
            y1 = this.origin.offset().top;
            x2 = this.target.offset().left;
            y2 = this.target.offset().top;
            originx = x1;
            originy = y1;
            diffx = x2-x1;
            diffy = y2-y1,
            speedx = diffx/this.time;

            // 已知a, 根据抛物线函数 y = a*x*x + b*x + c 将抛物线起点平移到坐标原点[0, 0]，终点随之平移，那么抛物线经过原点[0, 0] 得出c = 0;
            // 终点平移后得出：y2-y1 = a*(x2 - x1)*(x2 - x1) + b*(x2 - x1)
            // 即 diffy = a*diffx*diffx + b*diffx;
            // 可求出常数b的值
            b = (diffy - this.a*diffx*diffx)/diffx;
            this.element.css({
                left: x1,
                top: y1
            })
            return this;
        }

        // 确定动画方式
        this.moveStyle = function(){
            var moveStyle = ‘position‘,
                testDiv = document.createElement(‘div‘);
            if(‘placeholder‘ in testDiv){
                [‘‘,‘ms‘,‘moz‘,‘webkit‘].forEach(function(pre){
                    var transform = pre + (pre ? ‘T‘ : ‘t‘) + ‘ransform‘;
                    if(transform in testDiv.style){
                        moveStyle = transform;
                    }
                })
            }
            return moveStyle;
        }

        this.move = function(){
            var start = new Date().getTime(),
                moveStyle = this.moveStyle(),
                _this = this;
            timer = setInterval(function(){
                if(new Date().getTime() - start > _this.time){
                    clearInterval(timer);
                    _this.element.css({
                        left: x2,
                        top: y2
                    })
                    typeof _this.config.callback === ‘function‘ && _this.config.callback(_this.element);
                    return;
                }
                x = speedx * (new Date().getTime() - start);
                y = _this.a*x*x + b*x;
                if(moveStyle === ‘position‘){
                    _this.element.css({
                        left: x+originx,
                        top: y+originy
                    })
                }else{
                    if(window.requestAnimationFrame){
                        window.requestAnimationFrame(_this.element[0].style[moveStyle] = ‘translate(‘+x+‘px,‘+y+‘px)‘);
                    }else{
                        _this.element[0].style[moveStyle] = ‘translate(‘+x+‘px,‘+y+‘px)‘;
                    }
                }
            },INTERVAL)
            return this;
        }

        this.init();
    }