javascript设计模式单例

通过单例模式的方法创建的类只能有一个实例。

实现示例一 

class Manager{
    static InitTag=false;
    constructor(info){
        if(!Manager.InitTag){
            throw new Error("this is a singleton, can't be new, please call create function!");            
        }
        this.name=info.name;
        this.age=info.age;
    }
 
    static create(info){
        if(!Manager.instance){
            Manager.InitTag=true;
            Manager.instance=new Manager(info);
            Manager.InitTag=false;
        }
        return Manager.instance;
    }
 
    print(){
        console.log('name=',this.name,' age=',this.age);
    }
}
 
let info={name:'Andy',age:50};
let m=Manager.create(info);
m.print();
 
// let b=new Manager();
// console.log(b);

示例二使用单例实现对浏览器localstorage进行管理

class Storage {
    static InitStorage = false;
 
    constructor() {
        if(!Storage.InitStorage){
            throw new Error("this is a singleton, can't be new, please call getInstance function!");  
        }
    }
 
    static getInstance = () => {
        if (!Storage.instance) {
            Storage.InitStorage = true;
            Storage.instance = new Storage();
            Storage.InitStorage = false;
        }
        return Storage.instance;
    };
 
    setState(key, value) {
        window.localStorage.setItem(key, value);
    }
 
    getState(key) {
        return window.localStorage.getItem(key);
    }
 
    show = () => {
        console.log(window.localStorage);
    };
}
 
// let s = new Storage();
// console.log(s);
let m=Storage.getInstance();
console.log(m);