策略模式在JavaScript中的实现

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2023年09月20日 09:45 · 阅读数 17

策略模式（Strategy Pattern）是一种行为设计模式，它允许在运行时根据不同的情况选择不同的算法或行为。该模式将算法封装成独立的

策略对象，使得这些策略对象可以互相替换，从而使得算法的变化独立于使用算法的客户端。 -- 来自查特著迪皮

需求

想要实现一个功能，点击不同按钮实现不同样式

策略模式在JavaScript中的实现

原始代码

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    section {
      display: flex;
      padding: 10px;
    }

    button {
      margin: 0 10px;
      background-color: slateblue;
      outline: none;
      color: #fff;
      width: 100px;
      height: 100px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    div {
      width: 100px;
      height: 100px;
      margin: 50px auto;
      background-color: gray;
    }
  </style>
</head>

<body>
  <section>
    <button id="blue">蓝色 高度30</button>
    <button id="red">红色 高度40</button>
    <button id="green">绿色 高度50</button>
    <button id="purple">紫色 高度60</button>
    <button id="yellow">黄色 高度70</button>
  </section>
  <div>div</div>
  <script>
    const buttons = document.querySelectorAll("button");
    const div = document.querySelector("div");
    buttons.forEach(button => button.addEventListener('click', function (e) {
      const idType = button.id;
      // 重点代码=======================
      if (idType === "blue") {
        div.style.backgroundColor = "blue";
        div.style.height = "30px";
      }
      if (idType === "red") {
        div.style.backgroundColor = "red";
        div.style.height = "40px";
      }
      if (idType === "green") {
        div.style.backgroundColor = "green";
        div.style.height = "50px";
      }
      if (idType === "purple") {
        div.style.backgroundColor = "purple";
        div.style.height = "60px";
      }
      if (idType === "yellow") {
        div.style.backgroundColor = "yellow";
        div.style.height = "70px";
      }
      // 重点代码=======================
    }))
  </script>
</body>

</html>

问题

以上代码，明显存在冗余、不方便维护的问题。也就是违背了开放-封闭原则 （Open-Close Principle，OCP）

策略模式在JavaScript中的实现

分析

以上问题就很适合使用 策略模式

在JavaScript中，策略模式可以通过以下方式理解：

定义策略对象：首先，你需要定义一组策略对象，每个策略对象代表一种算法或行为。
使用策略对象：在需要使用算法或行为的地方，你可以通过选择合适的策略对象来实现不同的功能。这样可以在不修改客户端代码的情况下改变算法或行为。
切换策略：由于策略对象具有相同的接口，你可以根据不同的情况或条件来切换使用不同的策略对象。这使得你可以根据需要动态地选择合适的策略。

根据以上的分析，其实我们只需要换一个优雅的方式来替代高频率的 if-else即可。因为以上过程只需要表示为

策略模式在JavaScript中的实现

解决方案 1 普通对象

在JavaScript中，对象 object 天然具备 判断哪种策略 - 使用策略能力

对象[策略]();
obj[key]();

// 定义策略对象
const strategy = {
  blue(dom) {
    dom.style.backgroundColor = "blue";
    dom.style.height = "30px";
  },
  red(dom) {
    dom.style.backgroundColor = "red";
    dom.style.height = "40px";
  },
  green(dom) {
    dom.style.backgroundColor = "green";
    dom.style.height = "50px";
  },
  purple(dom) {
    dom.style.backgroundColor = "purple";
    dom.style.height = "60px";
  },
  yellow(dom) {
    dom.style.backgroundColor = "yellow";
    dom.style.height = "70px";
  },
}
buttons.forEach(button => button.addEventListener('click', function (e) {
  const idType = button.id;
  // 重点代码=======================
  // 判断和使用策略
  strategy[idType](div);
  // 重点代码=======================
}))

解决方案 2 prototype

以上代码，可以实现 es5基于构造函数的面向对象的思想来实现

定义策略对象

// 定义策略对象
const StrategyBlue = function () { }
const StrategyRed = function () { }
const StrategyGreen = function () { }
const StrategyPurple = function () { }
const StrategyYellow = function () { }

定义策略对应的行为

StrategyBlue.prototype.setStyle = function (dom) {
  dom.style.backgroundColor = "blue";
  dom.style.height = "30px";
}
StrategyRed.prototype.setStyle = function (dom) {
  dom.style.backgroundColor = "red";
  dom.style.height = "40px";
}
StrategyGreen.prototype.setStyle = function (dom) {
  dom.style.backgroundColor = "green";
  dom.style.height = "50px";
}
StrategyPurple.prototype.setStyle = function (dom) {
  dom.style.backgroundColor = "purple";
  dom.style.height = "60px";
}
StrategyYellow.prototype.setStyle = function (dom) {
  dom.style.backgroundColor = "yellow";
  dom.style.height = "70px";
}

定义不同的按钮和策略的映射关系

const mapStrategyType = {
  blue() {
    return new StrategyBlue()
  },
  red() {
    return new StrategyRed()
  },
  green() {
    return new StrategyGreen()
  },
  purple() {
    return new StrategyPurple()
  },
  yellow() {
    return new StrategyYellow()
  },
}

定义负责消费策略的对象

// 负责使用策略的对象
function DomElement() {
  this.dom = "";
  this.strategy = "";
}
DomElement.prototype.setDom = function (dom) {
  this.dom = dom;
}
DomElement.prototype.setStrategy = function (strategy) {
  this.strategy = strategy;
}
DomElement.prototype.executeStrategy = function (strategy) {
  this.strategy.setStyle(this.dom);
}

完整代码

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    section {
      display: flex;
      padding: 10px;
    }

    button {
      margin: 0 10px;
      background-color: slateblue;
      outline: none;
      color: #fff;
      width: 100px;
      height: 100px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    div {
      width: 100px;
      height: 100px;
      margin: 50px auto;
      background-color: gray;
    }
  </style>
</head>

<body>
  <section>
    <button id="blue">蓝色 高度30</button>
    <button id="red">红色 高度40</button>
    <button id="green">绿色 高度50</button>
    <button id="purple">紫色 高度60</button>
    <button id="yellow">黄色 高度70</button>
  </section>
  <div>div</div>
  <script>
    const buttons = document.querySelectorAll("button");
    const div = document.querySelector("div");

    // 定义策略对象
    const StrategyBlue = function () { }
    const StrategyRed = function () { }
    const StrategyGreen = function () { }
    const StrategyPurple = function () { }
    const StrategyYellow = function () { }

    // 定义策略映射关系
    const mapStrategyType = {
      blue() {
        return new StrategyBlue()
      },
      red() {
        return new StrategyRed()
      },
      green() {
        return new StrategyGreen()
      },
      purple() {
        return new StrategyPurple()
      },
      yellow() {
        return new StrategyYellow()
      },
    }



    StrategyBlue.prototype.setStyle = function (dom) {
      dom.style.backgroundColor = "blue";
      dom.style.height = "30px";
    }
    StrategyRed.prototype.setStyle = function (dom) {
      dom.style.backgroundColor = "red";
      dom.style.height = "40px";
    }
    StrategyGreen.prototype.setStyle = function (dom) {
      dom.style.backgroundColor = "green";
      dom.style.height = "50px";
    }
    StrategyPurple.prototype.setStyle = function (dom) {
      dom.style.backgroundColor = "purple";
      dom.style.height = "60px";
    }
    StrategyYellow.prototype.setStyle = function (dom) {
      dom.style.backgroundColor = "yellow";
      dom.style.height = "70px";
    }

    // 负责使用策略的对象
    function DomElement() {
      this.dom = "";
      this.strategy = "";
    }
    DomElement.prototype.setDom = function (dom) {
      this.dom = dom;
    }
    DomElement.prototype.setStrategy = function (strategy) {
      this.strategy = strategy;
    }
    DomElement.prototype.executeStrategy = function (strategy) {
      this.strategy.setStyle(this.dom);
    }

    // 负责消费策略的实例
    const domelement = new DomElement();
    buttons.forEach(button => button.addEventListener('click', function (e) {
      const idType = button.id;
      const strategy = mapStrategyType[idType]();// 根据type返回对应策略实例
      // 重点代码=======================
      domelement.setDom(div);// 设置要操作的dom
      domelement.setStrategy(strategy);// 设置策略
      domelement.executeStrategy();// 调用策略
      // 重点代码=======================
    }))
  </script>
</body>

</html>

解决方案 3 class

该版本使用 es6的class来替换面向对象的语法

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    section {
      display: flex;
      padding: 10px;
    }

    button {
      margin: 0 10px;
      background-color: slateblue;
      outline: none;
      color: #fff;
      width: 100px;
      height: 100px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    div {
      width: 100px;
      height: 100px;
      margin: 50px auto;
      background-color: gray;
    }
  </style>
</head>

<body>
  <section>
    <button id="blue">蓝色 高度30</button>
    <button id="red">红色 高度40</button>
    <button id="green">绿色 高度50</button>
    <button id="purple">紫色 高度60</button>
    <button id="yellow">黄色 高度70</button>
  </section>
  <div>div</div>
  <script>
    const buttons = document.querySelectorAll("button");
    const div = document.querySelector("div");

    // 定义策略对象
    class StrategyBlue {
      setStyle(dom) {
        dom.style.backgroundColor = "blue";
        dom.style.height = "30px";
      }
    }
    class StrategyRed {
      setStyle(dom) {
        dom.style.backgroundColor = "red";
        dom.style.height = "40px";
      }
    }
    class StrategyGreen {
      setStyle(dom) {
        dom.style.backgroundColor = "green";
        dom.style.height = "50px";
      }
    }
    class StrategyPurple {
      setStyle(dom) {
        dom.style.backgroundColor = "purple";
        dom.style.height = "60px";
      }
    }
    class StrategyYellow {
      setStyle(dom) {
        dom.style.backgroundColor = "yellow";
        dom.style.height = "70px";
      }
    }

    // 定义策略映射关系
    const mapStrategyType = {
      blue() {
        return new StrategyBlue()
      },
      red() {
        return new StrategyRed()
      },
      green() {
        return new StrategyGreen()
      },
      purple() {
        return new StrategyPurple()
      },
      yellow() {
        return new StrategyYellow()
      },
    }


    // 负责使用策略的对象
    class DomElement {
      constructor() {
        this.dom = "";
        this.strategy = "";
      }
      setDom(dom) {
        this.dom = dom;
      }
      setStrategy(strategy) {
        this.strategy = strategy;
      }
      executeStrategy = function (strategy) {
        this.strategy.setStyle(this.dom);
      }
    }


    // 负责消费策略的实例
    const domelement = new DomElement();
    buttons.forEach(button => button.addEventListener('click', function (e) {
      const idType = button.id;
      const strategy = mapStrategyType[idType]();// 根据type返回对应策略实例
      // 重点代码=======================
      domelement.setDom(div);// 设置要操作的dom
      domelement.setStrategy(strategy);// 设置策略
      domelement.executeStrategy();// 调用策略
      // 重点代码=======================
    }))
  </script>
</body>

</html>

优化神奇canvas 实现魔法摄像头的代码

可以看到，而已根据自身项目情况来考虑使用哪个版本的策略模式 以下提供优化后的代码

<!DOCTYPE html>
<html>

<head>
  <title>Canvas Demo</title>
  <style>
    button {
      border-radius: 10px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      overflow: hidden;
      user-select: none;
      outline: none;
      border: none;
      padding: 16px;
      background-color: #1d93ab;
      color: #fff;
    }

    button:focus {
      background-color: #e88f21
    }
  </style>
</head>

<body>
  <div>
    <button data-type="gray">反转</button>
    <button data-type="blackwhite">黑白</button>
    <button data-type="brightness">亮度</button>
    <button data-type="sepia">复古</button>
    <button data-type="redMask">红色</button>
    <button data-type="greenMask">绿色</button>
    <button data-type="blueMask">蓝色</button>
    <button data-type="opacity">透明</button>
    <button data-type="mosaic">马赛克</button>
    <button data-type="linearGradient">渐变</button>
    <button id="takePhoto">拍摄</button>
  </div>
  <video id="videoElement" autoplay></video>
  <canvas id="canvasElement"></canvas>

  <script>
    // 获取视频元素和画布元素
    const video = document.getElementById('videoElement');
    const canvas = document.getElementById('canvasElement');
    const ctx = canvas.getContext('2d');
    const buttons = document.querySelectorAll("button[data-type]");
    const takePhoto = document.querySelector("#takePhoto")// 截图 按钮
    let drawType = ""
    // 当视频元素加载完成后执行
    video.addEventListener('loadedmetadata', function () {
      // 设置画布大小与视频尺寸相同
      canvas.width = video.videoWidth;
      canvas.height = video.videoHeight;
    });

    // 操作类型
    const editType = {
      dataTypeList: ["gray", "blackwhite", "brightness", "sepia", "redMask", "greenMask", "blueMask", "opacity", "linearGradient"],
      // 后续继续补充
    }
    const handleData = {
      gray(data) {  // 反转
        for (let i = 0; i < data.length; i += 4) {
          data[i + 0] = 255 - data[i + 0];
          data[i + 1] = 255 - data[i + 1];
          data[i + 2] = 255 - data[i + 2];
        }
        return data
      },
      blackwhite(data) {
        for (let i = 0; i < data.length; i += 4) {
          const average = (data[i + 0] + data[i + 1] + data[i + 2] + data[i + 3]) / 3;
          data[i + 0] = average;//红

          data[i + 1] = average; //绿

          data[i + 2] = average; //蓝
        }
        return data
      },
      brightness(data) {
        for (let i = 0; i < data.length; i += 4) {
          const a = 50;
          data[i + 0] += a;
          data[i + 1] += a;
          data[i + 2] += a;
        }
        return data
      },
      sepia(data) {
        for (let i = 0; i < data.length; i += 4) {
          const r = data[i + 0];
          const g = data[i + 1];
          const b = data[i + 2];
          data[i + 0] = r * 0.39 + g * 0.76 + b * 0.18;
          data[i + 1] = r * 0.35 + g * 0.68 + b * 0.16;
          data[i + 2] = r * 0.27 + g * 0.53 + b * 0.13;
        }
        return data
      },
      redMask(data) {
        for (let i = 0; i < data.length; i += 4) {
          const r = data[i + 0]
          const g = data[i + 1]
          const b = data[i + 2]
          const average = (r + g + b) / 3
          data[i + 0] = average
          data[i + 1] = 0
          data[i + 2] = 0
        }
        return data
      },
      greenMask(data) {
        for (let i = 0; i < data.length; i += 4) {
          const r = data[i + 0]
          const g = data[i + 1]
          const b = data[i + 2]
          const average = (r + g + b) / 3
          data[i + 0] = 0
          data[i + 1] = average
          data[i + 2] = 0
        }
        return data
      },
      blueMask(data) {
        for (let i = 0; i < data.length; i += 4) {
          const r = data[i + 0]
          const g = data[i + 1]
          const b = data[i + 2]
          const average = (r + g + b) / 3
          data[i + 0] = 0
          data[i + 1] = 0
          data[i + 2] = average
        }
        return data
      },
      opacity(data) {
        for (let i = 0; i < data.length; i += 4) {
          data[i + 3] = data[i + 3] * 0.3;
        }
        return data
      },
      linearGradient(data) {
        for (let i = 0; i < data.length; i += 4) {
          const x = (i / 4) % canvas.width; // 当前像素的 x 坐标
          const y = Math.floor(i / (4 * canvas.width)); // 当前像素的 y 坐标

          // 计算当前像素的颜色值
          const r = x / canvas.width * 255; // 红色分量
          const g = y / canvas.height * 255; // 绿色分量
          const b = 128; // 蓝色分量
          const a = 100; // 不透明度

          // 设置当前像素的颜色值
          data[i] = r; // 红色分量
          data[i + 1] = g; // 绿色分量
          data[i + 2] = b; // 蓝色分量
          data[i + 3] = a; // 不透明度
        }
        return data
      },
      mosaic(ctx, canvas) {
        ctx.imageSmoothingEnabled = false; // 禁用图像平滑处理
        const tileSize = 10; // 马赛克块的大小
        // 缩小马赛克块
        ctx.drawImage(canvas, 0, 0, canvas.width, canvas.height, 0, 0, canvas.width / tileSize, canvas.height / tileSize);
        // 放大回原来的大小
        ctx.drawImage(canvas, 0, 0, canvas.width / tileSize, canvas.height / tileSize, 0, 0, canvas.width, canvas.height);
      },
    }

    // 在每一帧绘制视频画面到画布上
    function drawFrame() {
      ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
      const imageObj = ctx.getImageData(0, 0, canvas.width, canvas.height);

      if (editType.dataTypeList.includes(drawType)) {
        imageObj.data = handleData[drawType](imageObj.data);
        ctx.putImageData(imageObj, 0, 0);
      } else if (drawType === "mosaic") {
        // 马赛克
        handleData[drawType](ctx, canvas);
      }

      requestAnimationFrame(drawFrame);
      // setTimeout(drawFrame, 1000);
    }

    // 检查浏览器是否支持 getUserMedia API
    if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
      // 请求访问摄像头
      navigator.mediaDevices.getUserMedia({ video: true })
        .then(function (stream) {
          // 将视频流绑定到视频元素上
          video.srcObject = stream;
          // 开始绘制视频画面到画布上
          requestAnimationFrame(drawFrame);
        })
        .catch(function (error) {
          console.error('无法访问摄像头:', error);
        });
    } else {
      console.error('浏览器不支持 getUserMedia API');
    }

    buttons.forEach(button => {
      button.addEventListener("click", function (e) {
        drawType = e.target.dataset.type;
      })

    })

    takePhoto.addEventListener('click', function (e) {
      // 绘制原始 Canvas 的内容到新的 Canvas 上
      ctx.drawImage(canvas, 0, 0, canvas.width, canvas.height);

      // 将内容转换为数据 URL
      const dataURL = canvas.toDataURL();

      // 创建一个 <a> 元素并设置属性
      const link = document.createElement('a');
      link.href = dataURL;
      link.download = 'screenshot.png'; // 设置要保存的文件名

      // 模拟点击 <a> 元素来触发下载
      link.click();
    })
  </script>
</body>

</html>

策略模式 在JavaScript中的实现

需求

原始代码

问题

分析

解决方案 1 普通对象

解决方案 2 prototype

定义策略对象

定义策略对应的行为

定义不同的按钮和策略的映射关系

定义负责消费策略的对象

完整代码

解决方案 3 class

优化 神奇canvas 实现魔法摄像头的代码

策略模式在JavaScript中的实现

优化神奇canvas 实现魔法摄像头的代码