定义
定义一系列算法，把它们一个个封装起来，并且使他们可以相互替代。
描述
在程序设计中，我们常常遇到类似的情况，要实现某一个功能有多种方案可以选择。比如一个压缩文件的程序，既可以选择zip算法，也可以选择gzip算法。这些算法灵活多样，而且可以随意互相替换。这种解决方案就是本文将要介绍的策略模式。
应用
策略模型实现缓动动画是一个重要应用。我们常用的jQuery的animate方法$(selector).animate(styles,speed,easing,callback)，我们可以给出speed、easing的类型，就能使选定元素展示相应的动画效果。jQuery在内部利用策略模式，做了大量的算法封装，Up主在学习jQuery的过程中，模仿了animate方法的实现，具体代码如下。
var utils = (function(){
var flag = "getComputedStyle" in window // 区分ie9以下的浏览器
//->getCss:获取元素的样式值
function getCss(curEle,attr){
if(flag){
var val = window.getComputedStyle(curEle,null)[attr]
}else{
if(attr === "opacity"){
var reg = /^alpha\(opacity=(\d+(\.\d+?:)?)\)$/
oldVal = curEle.currentStyle["filter"]
val = oldVal.replace(reg,function(){
return parseFloat(arguments[1]/100)
})
}else{
val = curEle.currentStyle[attr]
}
}
if(/^(-?\d+(\.\d+)?)(px)?$/.test(val)){
val = parseFloat(val)
}
return val
}
//->setCss:给当前元素的某一个样式属性设置值(增加在行内样式上的)
function setCss(curEle,attr, value){
if(attr === "opacity"){
curEle.style["opacity"] = value
curEle.style["alpha"] = "alpha(opacity=" + value*100 + ")"
return
}
if(attr === "float"){
curEle.style["cssFloat"] = value
curEle.style["styleFloat"] = value
return
}
var reg = /^width|height|top|bottom|left|right|((margin|padding)(Left|Top|Right|Bottom))$/
if(reg.test(attr)){
if(!isNaN(value)){
value +="px"
}
}
curEle.style[attr] = value
}
//->setGroupCss:给当前元素批量的设置样式属性值
function setGroupCss(curEle,options){
for(var key in options){
this.setCss(curEle,key,options[key])
}
}
//->css:此方法实现了获取、单独设置、批量设置元素的样式值
function css(curEle){
var arg = [].slice.call(arguments)
if(arg.length == 2){
if(typeof arg[1] === "string") {
return this.getCss(curEle, arg[1])
}
if(Object.prototype.toString.call(arg[1]) === "[object Object]"){
this.setGroupCss(curEle,arg[1])
}
}
if(arg.length === 3){
this.setCss(curEle,arg[1],arg[2])
}
}
return {
getCss,
setCss,
setGroupCss,
css,
}
})()
utils提供了改变css的工具方法，utils.css()第一个参数是元素对象curEle，第二个参数是获取/设置的样式width、color....，第三个参数是要设置的值，模仿jQuery，获取/设置的像素值均为number类型，支持批量设置css样式。
~function(){
//->tween算法，t: curTime， b:begin， c:change(target-begin)， d:duration
let tween = {
//匀速
Linear: function (t, b, c, d) {
return c * t / d + b;
},
//指数衰减的反弹缓动
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;
}
return tween.Bounce.easeOut(t * 2 - d, 0, c, d) * .5 + c * .5 + b;
}
},
//二次方的缓动
Quad: {
easeIn: function (t, b, c, d) {
return c * (t /= d) * t + b;
},
easeOut: function (t, b, c, d) {
return -c * (t /= d) * (t - 2) + b;
},
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;
}
},
//三次方的缓动
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;
}
},
//四次方的缓动
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;
}
},
//五次方的缓动
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;
}
},
//正弦曲线的缓动
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;
}
},
//指数曲线的缓动
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;
}
}
}
/* animate的效果effect的支持
* 1.支持传入数字 0->tween.Linear 1->tween.Bounce.easeInOut 2->tween.Quad.easeOut 3->tween.Cubic.easeOut 4->tween.Quart.easeOut 5->tween.Expo.easeIn
* 2.支持传入数组 ["Quart","easeOut"]) ->tween.Quart.easeOut
* 3.默认值 undefined:tween.Linear
*/
/**
* @method animate
* @Description 利用tween动画库，实现缓动动画
* @params curEle:当前元素,target：目标点的位置，是一个{}，duration:动画运动时间(ms),effect:tween动画库一种效果,callback：动画完成时执行回调
* @return undefined
*/
function animate(curEle, target, duration, effect, callback){
var curEffect = tween.Linear;
if(typeof effect === "number"){
switch (effect){
case 0:
curEffect = tween.Linear;
case 1:
curEffect = tween.Bounce.easeInOut;
break;
case 2:
curEffect = tween.Quad.easeOut;
break;
case 3:
curEffect = tween.Cubic.easeOut;
break;
case 4:
curEffect = tween.Quart.easeOut;
break;
case 5:
curEffect = tween.Expo.easeIn;
break;
}
}else if(effect instanceof Array){
if(effect.length ===2){
curEffect = tween[effect[0]][effect[1]];
}
}else if(typeof effect === "function"){
callback = effect;
}
var begin ={},change = {};
for( var key in target){
begin[key] = utils.css(curEle,key);
change[key] = target[key] - begin[key];
}
var time = 0;
curEle.timer = window.setInterval(function(){
time +=10;
if(time >= duration){
utils.css(curEle,target);
window.clearInterval(curEle.timer);
callback && callback();
return;
}
for(var key in target){
var curPos = curEffect(time, begin[key], change[key], duration);
utils.css(curEle,key,curPos);
}
},10);
}
window.animate = animate;
}();
aniamte方法的使用：
var box = document.getElementById('box')
animate(box, {opacity:0.5}, 1000, 2, function () {
alert('success')
})