var Tween = { // t => 当前是第几步(总步数 = 总执行时间/每次执行时间(setInterval中的时间)) // b => 开始值 // c =>变化量 即 终点值-开始值 // d => 经过多少次到达 //匀速的线性运动 Linear: function (t, b, c, d) { return c * t / d + b; }, //变速线性运动 //二次方加速 Quad: { // 速度递增 越来越快 easeIn: function (t, b, c, d) { return c * (t /= d) * t + b; }, // 速度递减 越来越慢 easeOut: function (t, b, c, d) { return -c * (t /= d) * (t - 2) + b; }, // 先加速再加速 easeInOut: function (t, b, c, d) { if ((t /= d / 2) < 1) return c / 2 * t * t + b; return -c / 2 * ((--t) * (t - 2) - 1) + b; } }, //变速线性运动 //三次方加速 加速幅度比二次方块 Cubic: { easeIn: function (t, b, c, d) { return c * (t /= d) * t * t + b; }, easeOut: function (t, b, c, d) { return c * ((t = t / d - 1) * t * t + 1) + b; }, easeInOut: function (t, b, c, d) { if ((t /= d / 2) < 1) return c / 2 * t * t * t + b; return c / 2 * ((t -= 2) * t * t + 2) + b; } }, //变速线性运动 //四次方加速 Quart: { easeIn: function (t, b, c, d) { return c * (t /= d) * t * t * t + b; }, easeOut: function (t, b, c, d) { return -c * ((t = t / d - 1) * t * t * t - 1) + b; }, easeInOut: function (t, b, c, d) { if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b; return -c / 2 * ((t -= 2) * t * t * t - 2) + b; } }, //变速线性运动 //五次方加速 Quint: { easeIn: function (t, b, c, d) { return c * (t /= d) * t * t * t * t + b; }, easeOut: function (t, b, c, d) { return c * ((t = t / d - 1) * t * t * t * t + 1) + b; }, easeInOut: function (t, b, c, d) { if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b; return c / 2 * ((t -= 2) * t * t * t * t + 2) + b; } }, //运动更平滑 Sine: { easeIn: function (t, b, c, d) { return -c * Math.cos(t / d * (Math.PI / 2)) + c + b; }, easeOut: function (t, b, c, d) { return c * Math.sin(t / d * (Math.PI / 2)) + b; }, easeInOut: function (t, b, c, d) { return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b; } }, //加速减速更快 Expo: { easeIn: function (t, b, c, d) { return (t == 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b; }, easeOut: function (t, b, c, d) { return (t == d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b; }, easeInOut: function (t, b, c, d) { if (t == 0) return b; if (t == d) return b + c; if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b; return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b; } }, Circ: { easeIn: function (t, b, c, d) { return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b; }, easeOut: function (t, b, c, d) { return c * Math.sqrt(1 - (t = t / d - 1) * t) + b; }, easeInOut: function (t, b, c, d) { if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b; return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b; } }, // 弹性运动 //激烈 Elastic: { // 运动前弹动 easeIn: function (t, b, c, d, a, p) { if (t == 0) return b; if ((t /= d) == 1) return b + c; if (!p) p = d * .3; if (!a || a < Math.abs(c)) { a = c; var s = p / 4; } else var s = p / (2 * Math.PI) * Math.asin(c / a); return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b; }, // 运动到终点后弹动 easeOut: function (t, b, c, d, a, p) { if (t == 0) return b; if ((t /= d) == 1) return b + c; if (!p) p = d * .3; if (!a || a < Math.abs(c)) { a = c; var s = p / 4; } else var s = p / (2 * Math.PI) * Math.asin(c / a); return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b); }, // 前后都弹动 easeInOut: function (t, b, c, d, a, p) { if (t == 0) return b; if ((t /= d / 2) == 2) return b + c; if (!p) p = d * (.3 * 1.5); if (!a || a < Math.abs(c)) { a = c; var s = p / 4; } else var s = p / (2 * Math.PI) * Math.asin(c / a); if (t < 1) return -.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b; return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * .5 + c + b; } }, //弹性运动 //只回弹一次 //较缓慢 Back: { easeIn: function (t, b, c, d, s) { if (s == undefined) s = 1.70158; return c * (t /= d) * t * ((s + 1) * t - s) + b; }, easeOut: function (t, b, c, d, s) { if (s == undefined) s = 1.70158; return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b; }, easeInOut: function (t, b, c, d, s) { if (s == undefined) s = 1.70158; if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b; return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b; } }, //回弹2次 //较缓慢 Back快点 Bounce: { easeIn: function (t, b, c, d) { return c - Tween.Bounce.easeOut(d - t, 0, c, d) + b; }, easeOut: function (t, b, c, d) { if ((t /= d) < (1 / 2.75)) { return c * (7.5625 * t * t) + b; } else if (t < (2 / 2.75)) { return c * (7.5625 * (t -= (1.5 / 2.75)) * t + .75) + b; } else if (t < (2.5 / 2.75)) { return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b; } else { return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b; } }, easeInOut: function (t, b, c, d) { if (t < d / 2) return Tween.Bounce.easeIn(t * 2, 0, c, d) * .5 + b; else return Tween.Bounce.easeOut(t * 2 - d, 0, c, d) * .5 + c * .5 + b; } } }
返回值为当前步数或者说时间（有误差）内，在开始状态和结束状态中间应该变化的值。
相对与不断获取位置，然后计算下一次应该运动距离，效率更高
如
obj.timer = setInterval(function(){ obj.animate = true; //getStyle 通过 current或者computedStyle 获取到的元素当前状CSS的值。 //可想而知，每秒钟获取N多次，效率肯定低下。 var cur = parseInt(getStyle(obj,attr)); //同样的不断执行parseInt cur = attr.toLowerCase()=='opacity'?parseInt(getStyle(obj,attr)*100):cur; //不断变化下一次移动的距离 递减 var speed = (target - cur)/8; speed = speed>0 ? Math.ceil(speed):Math.floor(speed); if(cur == target){ obj.animate = false; clearInterval(obj.timer); if(fn){ fn.call(obj); // 动画结束 执行回调函数 } }else{ setStyle(obj,attr,cur+speed); } },30);