JavaScript设计模式-----命令模式的简单应用

命令模式是最简单和优雅的模式之一，命令模式中的命令（command）是指一个执行某些特定事情的指令。

应用场景：有时候需要向某些对象发送请求，但是并不知道请求的接受者是谁，也不知道被请求的操作是什么，此时希望用一种

松解耦的方式来设计软件，使得请求发送者和请求接受者能够消除彼此之间的耦合关系。

一个简单JavaScript例子：

 <!DOCTYPE html>

 <html lang="en">

 <head>

     <meta charset="UTF-8">

     <title>命令模式</title>

     <style>

         body{

             padding:  0;

             margin: 0;

         }

         .ball{

             position: absolute;

             background: #000;

             width: 50px;

             height: 50px;

             top:  200px;

         }

     </style>

 </head>

 <body>

     <div id="ball" class="ball"></div>

     输入小球移动后的位置：<input type="text" id="pos">

     <button id="moveBtn">开始移动</button>

     <button id="cancelBtn">cancel</button>

     <script>

         // 营运策略模式封装一系列缓动算法

         // t:已消耗的时间 b:小球的原始位置   c:小球的目标位置  d:动画持续的总时间

         // 返回当前位置

         var tween = {

             linear: function(t, b, c, d) {

                 return c*t/d + b;

             },

             easeIn: function(t, b, c, d) {

                 return c * (t /= d) * t + b;

             },

             strongEaseIn: function(t, b, c, d) {

                 return c * (t /= d) * t * t * t + b;

             },

             strongEaseOut: function(t, b, c, d) {

                 return c * (( t = t / d - 1 ) * t * t * t * t + 1) + b;

             },

             sineaseIn: function(t, b, c, d) {

                 return c * (t /= d) * t * t + b;

             },

             sineaseOut: function(t, b, c, d) {

                 return c * (( t = t / d - 1) * t * t + 1) + b;

             }

         };

         // 定义动画类

         var Animate = function(dom) {

             this.dom = dom;

             this.startTime = 0;

             this.startPos = 0;

             this.endPos = 0;

             this.propertyName = null;

             this.easing = null;

             this.duration = null;

         }

         // 动画启动

         Animate.prototype.start = function(propertyName, endPos, duration, easing) {

             this.propertyName = propertyName;

             this.startTime = +new Date();

             this.startPos = this.dom.getBoundingClientRect()[propertyName];

             this.endPos = endPos;

             this.duration = duration;

             this.easing = tween[easing];

             var self = this;

             var timeId = setInterval(function() {

                 if (self.step() === false) {

                     clearInterval(timeId);

                 }

             }, 1000/60)

         }

         Animate.prototype.step = function() {

             var t = +new Date();

             if (t > this.startTime + this.duration) {

                 this.update(this.endPos);

                 return false;

             }

             var pos = this.easing(t - this.startTime,

                 this.startPos, this.endPos - this.startPos, this.duration);

             this.update(pos);

         }

         Animate.prototype.update = function( pos ) {

             this.dom.style[ this.propertyName ] = pos + 'px';

         }

         var ball = document.getElementById('ball');

         var pos = document.getElementById('pos');

         var moveBtn = document.getElementById('moveBtn');

         var cancelBtn = document.getElementById('cancelBtn');

         // 使用命令模式实现事件和dom的解耦

         var MoveCommand = function(receiver, pos) {

             this.receiver = receiver;

             this.pos = pos;

             this.oldPos = null;

         }

         MoveCommand.prototype.excute = function() {

             this.receiver.start('left', this.pos, 1000, 'strongEaseOut');

             this.oldPos = this.receiver.dom.getBoundingClientRect()[this.receiver.propertyName];

         }

         MoveCommand.prototype.undo = function() {

             this.receiver.start('left', this.oldPos, 1000, 'strongEaseOut');

         }

         var moveCommand;

         moveBtn.onclick = function() {

             var animate = new Animate( ball );

             moveCommand = new MoveCommand(animate, pos.value);

             moveCommand.excute();

         }

         cancelBtn.onclick = function() {

             console.log(moveCommand);

             moveCommand.undo();

         }

     </script>

 </body>

 </html>

巴特西

JavaScript设计模式-----命令模式的简单应用

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