前端常用设计模式之单例模式

Posted 2021-09-14 ！win ！

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前情

在前端开发越来越复杂的今天，越来越需要一些设计模式来提高开发质量和效率

定义

属于创建型模式，这种模式涉及到一个单一的类，该类负责创建自己的对象，同时确保只有单个对象被创建。

代码演示

通过静态属性实现单例

class Person{
  static instance;
  constructor(name) {
    if (!Person.instance) {
      Person.instance = this;
    } else {
      return Person.instance;
    }
    this.name = name;
  }
}

let zhangsan = new Person("张三");
let lisi = new Person("李四");

console.log(zhangsan, lisi);
// Person { name: \'张三\' } Person { name: \'张三\' }

通用的单例实现

class Person{
  constructor(name) {
    this.name = name;
  }
}

// 通用单例
function createInstance(fn){
  let instance;
  return function(...args) {
    if (!instance) {
      instance = new fn(...args);
    }
    return instance;
  }
}

let singlePerson = createInstance(Person);
let zhangsan = singlePerson("张三");
let lisi = singlePerson("李四");
console.log(zhangsan, lisi);
// Person { name: \'张三\' } Person { name: \'张三\' }

实际应用

单例实现弹窗简易弹窗组件

<!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>单例弹窗</title>
  <style>
    html,body{
      padding: 0;
      margin: 0;
    }
    body{
      background-color: aquamarine;
    }
    .dialog{
      width: 300px;
      height: 150px;
      position: fixed;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
      border: 1px solid #ccc;
      border-radius: 2px;
      display: flex;
      justify-content: center;
      align-items: center;
      background-color: #fff;
    }
    .close{
      padding: 5px;
      position: absolute;
      top: 3px;
      right: 3px;
      cursor: pointer;
    }
  </style>
</head>
<body>
  <button id="dialogBtn">弹窗</button>
  <script>
    class Dialog{
      constructor() {
        this.dialog = document.createElement(\'div\');
        this.dialog.className = "dialog";
        this.dialog.style.display = "none";
        this.content = document.createElement(\'div\');
        this.close = document.createElement(\'span\');
        this.close.innerHTML = "X";
        this.close.className = "close";
        this.dialog.appendChild(this.content);
        this.dialog.appendChild(this.close);
        document.body.appendChild(this.dialog);
        this.show = false;
        let self = this;
        this.close.onclick = function() {
          self.hideDlg();
        };

      }
      showDlg(tips) {
        if (this.isShow) {
          return;
        }
        this.content.innerHTML = tips;
        this.dialog.style.display = "flex";
        this.isShow = true;
      }
      hideDlg() {
        if (!this.isShow) {
          return;
        }
        this.dialog.style.display = "none";
        this.isShow = false;
      }
    }

    // 通用单例
    function createInstance(fn){
      let instance;
      return function(...args) {
        if (!instance) {
          instance = new fn(...args);
        }
        return instance;
      }
    }

    let singleDialog = createInstance(Dialog);
    let dialog0 = singleDialog();
    let dialog1 = singleDialog();
    document.getElementById(\'dialogBtn\').onclick = function() {
      dialog0.showDlg(\'这是弹窗测试0\');
      dialog1.showDlg(\'这是弹窗测试1\');
    }
  </script>
</body>
</html>

演示示例：https://jsbin.com/hewanaloku/edit?html,output

好好学习！天天向上！

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