单例模式只能创建一个实例

        function Person(name) {
   
            this.name = name;
        }
        const p1 = new Person('qwe');
        const p2 = new Person('asd');
        console.log(p1 === p2);//false
        //p1和p2是两个不同的实例，如果每次都只想创建同一个实例，则可以使用单例模式

单例模式核心代码

        function Person(name) {
   
            this.name = name;
        }
        let instance = null;
        function singleTon(name) {
   
            if(!instance){
   
                instance = new Person(name);
            }
            return instance;
        }
        const p1 = singleTon('tyh');
        const p2 = singleTon('xyr');
        console.log(p1,p2);//p1和p2都是name='tyh'的实例
        console.log(p1 === p2);//true

通过闭包的方式将整个单例模式实现

        const Person = (function(){
   
            function Person(name,age,sex) {
   
                this.name = name;
                this.age = age;
                this.sex = sex;
            }
            Person.prototype.say = function() {
   
                console.log("hello");
            }
            let instance = null;
            return function singleTon(...arg){
   
                if(!instance) instance = new Person(...arg);
                return instance;
            }
        }());
        const p1 = new Person('tyh',12,'男');
        const p2 = new Person('xys',15,'女');
        console.log(p1,p2);
        console.log(p1 === p2);//true