js抛物线动画——加入购物车动效

参考文章：http://www.zhangxinxu.com/wordpress/2013/12/javascript-js-元素-抛物线-运动-动画/

parapola.js

 /*!
  * by zhangxinxu(.com) 2012-12-27
  * you can visit http://www.zhangxinxu.com/wordpress/?p=3855 to get more infomation
  * under MIT license
 */
 var funParabola = function(element, target, options) {
     /*
      * 网页模拟现实需要一个比例尺
      * 如果按照1像素就是1米来算，显然不合适，因为页面动不动就几百像素
      * 页面上，我们放两个物体，200~800像素之间，我们可以映射为现实世界的2米到8米，也就是100:1
      * 不过，本方法没有对此有所体现，因此不必在意
     */

     var defaults = {
         speed: 166.67, // 每帧移动的像素大小，每帧（对于大部分显示屏）大约16~17毫秒
         curvature: 0.001,  // 实际指焦点到准线的距离，你可以抽象成曲率，这里模拟扔物体的抛物线，因此是开口向下的
         progress: function() {},
         complete: function() {}
     };

     var params = {}; options = options || {};

     for (var key in defaults) {
         params[key] = options[key] || defaults[key];
     }

     var exports = {
         mark: function() { return this; },
         position: function() { return this; },
         move: function() { return this; },
         init: function() { return this; }
     };

     /* 确定移动的方式
      * IE6-IE8 是margin位移
      * IE9+使用transform
     */
     var moveStyle = "margin", testDiv = document.createElement("div");
     if ("oninput" in testDiv) {
         ["", "ms", "webkit"].forEach(function(prefix) {
             var transform = prefix + (prefix? "T": "t") + "ransform";
             if (transform in testDiv.style) {
                 moveStyle = transform;
             }
         });
     }

     // 根据两点坐标以及曲率确定运动曲线函数（也就是确定a, b的值）
     /* 公式： y = a*x*x + b*x + c;
     */
     var a = params.curvature, b = 0, c = 0;

     // 是否执行运动的标志量
     var flagMove = true;

     if (element && target && element.nodeType == 1 && target.nodeType == 1) {
         var rectElement = {}, rectTarget = {};

         // 移动元素的中心点位置，目标元素的中心点位置
         var centerElement = {}, centerTarget = {};

         // 目标元素的坐标位置
         var coordElement = {}, coordTarget = {};

         // 标注当前元素的坐标
         exports.mark = function() {
             if (flagMove == false) return this;
             if (typeof coordElement.x == "undefined") this.position();
             element.setAttribute("data-center", [coordElement.x, coordElement.y].join());
             target.setAttribute("data-center", [coordTarget.x, coordTarget.y].join());
             return this;
         }

         exports.position = function() {
             if (flagMove == false) return this;

             var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft,
                 scrollTop = document.documentElement.scrollTop || document.body.scrollTop;

             // 初始位置
             if (moveStyle == "margin") {
                 element.style.marginLeft = element.style.marginTop = "0px";
             } else {
                 element.style[moveStyle] = "translate(0, 0)";
             }

             // 四边缘的坐标
             rectElement = element.getBoundingClientRect();
             rectTarget = target.getBoundingClientRect();

             // 移动元素的中心点坐标
             centerElement = {
                 x: rectElement.left + (rectElement.right - rectElement.left) / 2 + scrollLeft,
                 y: rectElement.top + (rectElement.bottom - rectElement.top) / 2    + scrollTop
             };

             // 目标元素的中心点位置
             centerTarget = {
                 x: rectTarget.left + (rectTarget.right - rectTarget.left) / 2 + scrollLeft,
                 y: rectTarget.top + (rectTarget.bottom - rectTarget.top) / 2 + scrollTop
             };

             // 转换成相对坐标位置
             coordElement = {
                 x: 0,
                 y: 0
             };
             coordTarget = {
                 x: -1 * (centerElement.x - centerTarget.x),
                 y:  -1 * (centerElement.y - centerTarget.y)
             };

             /*
              * 因为经过(0, 0), 因此c = 0
              * 于是：
              * y = a * x*x + b*x;
              * y1 = a * x1*x1 + b*x1;
              * y2 = a * x2*x2 + b*x2;
              * 利用第二个坐标：
              * b = (y2+ a*x2*x2) / x2
             */
             // 于是
             b = (coordTarget.y - a * coordTarget.x * coordTarget.x) / coordTarget.x;    

             return this;
         };        

         // 按照这个曲线运动
         exports.move = function() {
             // 如果曲线运动还没有结束，不再执行新的运动
             if (flagMove == false) return this;

             var startx = 0, rate = coordTarget.x > 0? 1: -1;

             var step = function() {
                 // 切线 y'=2ax+b
                 var tangent = 2 * a * startx + b; // = y / x
                 // y*y + x*x = speed
                 // (tangent * x)^2 + x*x = speed
                 // x = Math.sqr(speed / (tangent * tangent + 1));
                 startx = startx + rate * Math.sqrt(params.speed / (tangent * tangent + 1));

                 // 防止过界
                 if ((rate == 1 && startx > coordTarget.x) || (rate == -1 && startx < coordTarget.x)) {
                     startx = coordTarget.x;
                 }
                 var x = startx, y = a * x * x + b * x;

                 // 标记当前位置，这里有测试使用的嫌疑，实际使用可以将这一行注释
                 element.setAttribute("data-center", [Math.round(x), Math.round(y)].join());

                 // x, y目前是坐标，需要转换成定位的像素值
                 if (moveStyle == "margin") {
                     element.style.marginLeft = x + "px";
                     element.style.marginTop = y + "px";
                 } else {
                     element.style[moveStyle] = "translate("+ [x + "px", y + "px"].join() +")";
                 }

                 if (startx !== coordTarget.x) {
                     params.progress(x, y);
                     window.requestAnimationFrame(step);
                 } else {
                     // 运动结束，回调执行
                     params.complete();
                     flagMove = true;
                 }
             };
             window.requestAnimationFrame(step);
             flagMove = false;

             return this;
         };

         // 初始化方法
         exports.init = function() {
             this.position().mark().move();
         };
     }

     return exports;
 };

 /*! requestAnimationFrame.js
  * by zhangxinxu 2013-09-30
 */
 (function() {
     var lastTime = 0;
     var vendors = ['webkit', 'moz'];
     for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
         window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
         window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||    // name has changed in Webkit
                                       window[vendors[x] + 'CancelRequestAnimationFrame'];
     }

     if (!window.requestAnimationFrame) {
         window.requestAnimationFrame = function(callback, element) {
             var currTime = new Date().getTime();
             var timeToCall = Math.max(0, 16.7 - (currTime - lastTime));
             var id = window.setTimeout(function() {
                 callback(currTime + timeToCall);
             }, timeToCall);
             lastTime = currTime + timeToCall;
             return id;
         };
     }
     if (!window.cancelAnimationFrame) {
         window.cancelAnimationFrame = function(id) {
             clearTimeout(id);
         };
     }
 }());

使用：

/* 元素 */
var element = document.getElementById("element"),
    target = document.getElementById("target");
// 抛物线元素的的位置标记
var parabola = funParabola(element, target).mark();
// 抛物线运动的触发
document.body.onclick = function() {
    element.style.marginLeft = "0px";
    element.style.marginTop = "0px";
    parabola.init();
};

加入购物车实战：

/* 本demo演示脚本基于ieBetter.js, 项目地址：https://github.com/zhangxinxu/ieBetter.js */

// 元素以及其他一些变量
var eleFlyElement = document.querySelector("#flyItem"), eleShopCart = document.querySelector("#shopCart");
var numberItem = 0;
// 抛物线运动
var myParabola = funParabola(eleFlyElement, eleShopCart, {
    speed: 400,
    curvature: 0.002,
    complete: function() {
        eleFlyElement.style.visibility = "hidden";
        eleShopCart.querySelector("span").innerHTML = ++numberItem;
    }
});
// 绑定点击事件
if (eleFlyElement && eleShopCart) {
    [].slice.call(document.getElementsByClassName("btnCart")).forEach(function(button) {
        button.addEventListener("click", function() {
            // 滚动大小
            var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft || 0,
                scrollTop = document.documentElement.scrollTop || document.body.scrollTop || 0;

            eleFlyElement.style.left = event.clientX + scrollLeft + "px";
            eleFlyElement.style.top = event.clientY + scrollTop + "px";
            eleFlyElement.style.visibility = "visible";

            // 需要重定位
            myParabola.position().move();
        });
    });
}