meaning

As the name implies, singletons literally mean singletons, and can also be understood to guarantee that a class has only one instance and provide a global access point to access it.Copy the code

Train of thought

When creating an object, check whether the object exists globally. If so, return the object. If not, create a new instance and return itCopy the code

Js implementation

  • ES5 implementation
   var Single = (function() {
   var instance = null;
   function Single(name) {
       this.name = name;
   }
   return function(name){
       if(! instance) { instance =new Single(name);
       }
       returninstance; }; }) ();var oA = new Single('hi');
   var oB = new Single('hello');
   console.log(oA===oB);
Copy the code

The first call to the constructor stores an instance with a closure, and subsequent calls return instance directly

  • ES6 implementation
  class Singleton {
   constructor(name) {
       this.name = name;
       this.instance = null;
   }
   static getInstance(name) {
       if(!this.instance) {
           this.instance = new Singleton(name);
       }
       return this.instance; }}var oA = Singleton.getInstance('hi');
 var oB = Singleton.getInstance('hisd');
 console.log(oA===oB);
Copy the code

A class is the prototype of an instance. All methods defined in a class are inherited by the instance. If you prefix a method with the static keyword, that method is not inherited by the instance.

  • Application of singleton pattern: only one common instance object is required globally, for example:

    • Log in to the popover component

    • A music playback program, if the user opened a music, and want to open a music, then the previous playback interface will automatically close, switch to the current playback interface. These are all application scenarios for the singleton pattern.

    • For any website, click the login button, and only one login box will pop up. Even if you click the login button again, another pop-up box will not pop up