【js进阶】设计模式之单例模式的几种声明方式

单例模式，简言之就是一个类无论实例化多少次，最终都是同一个对象

原生js的几个辅助方式的实现

手写forEch,map,filter

Array.prototype.MyForEach = function (callback) {for (let i = 0; i < this.length; i++) {callback(this[i], i, this);}
};const arr = [1, 2, 3];
arr.MyForEach((item, index, arr) => {console.log(item);console.log(index);console.log(arr);
});Array.prototype.MyFilter = function (callback) {const result = [];for (let i = 0; i < this.length; i++) {if (callback(this[i], i, this)) {result.push(this[i]);}}return result;
};const arr2 = [1, 2, 3, 5, 6, 7];
console.log(arr2.MyFilter((item) => item > 3));
console.log(arr2.MyFilter((item) => item < 5));Array.prototype.MyMap = function (callback) {const result = [];for (let i = 0; i < this.length; i++) {result.push(callback(this[i], i, this));}return result;
};console.log(arr2.MyMap((item) => item * 2));

在这里插入图片描述

基础单例模式

// 单体模式,
var SingleTon = {a1: true,a2: 10,method1() {console.log('单体模式1');},method2() {console.log('单体模式2');},
};SingleTon.a1 = false;
let total = SingleTon.a2 + 5;
let result = SingleTon.method1();// 全局命名空间
let GiantCorp = {};
GiantCorp.Common = {};
GiantCorp.ErrorCodes = {};
GiantCorp.PahgeHandler = {};// 私有成员，一是相互约定用下划线标注
GiantCorp.DataParse = {// 私有属性_name: '张三',// 私有方法_getName() {return this._name;},// 公有方法getUsername(nickname) {return this._getName() + nickname;},
};

改进版单例

let MyNamespace = {};
// 使用闭包封装私有变量
MyNamespace.SingleTon = (function () {let arr = ['张三', '李四', '王五'];return {name: '续航',age: 18,getName() {return this.name;},getAge() {return this.age;},getAllUserName() {return arr.join(',');},};
})();console.log(MyNamespace.SingleTon.getName());
console.log(MyNamespace.SingleTon.getAge());
console.log(MyNamespace.SingleTon.getAllUserName());

高阶版单例

// 惰性单体
let MyNamespace = {};
// 使用闭包封装私有变量
MyNamespace.SingleTon = (function () {let singleTon = null;function constructor() {let arr = ['张三', '李四', '王五'];return {name: '续航',age: 18,getName() {return this.name;},getAge() {return this.age;},getAllUserName() {return arr.join(',');},};}return {getInstance() {if (!singleTon) {singleTon = constructor(); // 创建实例对象，并将其赋值给私有变量}return singleTon; // 返回实例对象（单例模式）},};
})();
console.log(MyNamespace.SingleTon.getInstance().getName());
console.log(MyNamespace.SingleTon.getInstance().getAllUserName());

案例

let simpleXhrFactory = (function () {let standard = {createXHRObject() {return new XMLHttpRequest();},};let activexOld = {createXHRObject() {return new ActiveXObject('Microsoft.XMLHTTP');},};let activeXNew = {createXHRObject() {return new ActiveXObject('MSXML2.XMLHTTP');},};let xhr = null;try {xhr = standard.createXHRObject();return xhr;} catch (e) {try {xhr = activeXNew.createXHRObject();return xhr;} catch (e) {try {xhr = activeXOld.createXHRObject();} catch (error) {throw new Error('不支持的浏览器');}}}return xhr;
})();