What is the equivalent of Java singleton in React Native?

Question

Actually I am a Android Native Developer. I am new to React-Native. In Java i keep the users data and others data in Singleton Class and access from other activities. Then how i achieve this process in React native for access data's from other components or any alternative of singleton in React native.

I just try this but i received the error like getInstance() not defined.

class AppDelegate {
log = "This is AppDelegate";  

  static myInstance = null;
  static getInstance() {
    if (AppDelegate.myInstance == null) {
      AppDelegate.myInstance = new AppDelegate();
    }

    return this.myInstance;
  }

}

Thank you.

Possible duplicate of [singleton object in react native](https://stackoverflow.com/questions/44719103/singleton-object-in-react-native) — , Apr 24 '19 at 10:18
Not really a dupe because that question was badly worded, looks like it's about persistent storage. — Estus Flask, Apr 24 '19 at 10:33
@Sabish.M Your question is fine. I referred to this question that was linked above https://stackoverflow.com/questions/44719103/singleton-object-in-react-native , not yours. — Estus Flask, Apr 24 '19 at 11:00

Estus Flask · Answer 1 · 2019-04-24T10:21:14.997

4

React is UI library, this isn't its responsibility. The question affects any JavaScript application, not only React.

JavaScript modules and ES modules in particular are evaluated only once under normal circumstances, this makes exports singletons:

  // exported for extensibility
  export class AppDelegate {...}

  // a singleton
  export default new AppDelegate;

Singleton class is potentially an antipattern in JavaScript. If there's a need for one object, it could be written as object literal.

edited Apr 24 '19 at 10:21

answered Apr 24 '19 at 10:19

Estus Flask

206,104
70
425
565

Beaten in time, take advantage of import's caching is the better solution IMHO +1 – Mosè Raguzzini Apr 24 '19 at 10:20
I totally agree. – Estus Flask Apr 24 '19 at 10:23

Mosè Raguzzini · Accepted Answer · 2019-04-24T10:29:33.703

3

Imports are cached, so if you export a class, the class will be cached, if you export an instance, the instance will be cached

edited Apr 24 '19 at 10:29

answered Apr 24 '19 at 10:19

Mosè Raguzzini

15,399
1
31
43

I have another doubt? – Sabish.M May 14 '19 at 04:03
How to reset the class to initial state after import in somewhere? – Sabish.M May 14 '19 at 04:03

score 0 · Answer 3 · answered Apr 24 '19 at 10:42

If you need a singleton don't use a class at all. Export the methods as a function instead.

// File app-delegate.js
let privateIstanceValue;
export const method1 = () => //do something;
export const method2 = () => //do something again;

Import using import * as

import * as appDelegate from './app-delegate.js';

What is the equivalent of Java singleton in React Native?

3 Answers3

Linked