Use the same instance through out the code javascript

Question

Class Life {
   constructor(name = 'no name') {
     this.name = name;
   }
   getName() {
     return this.name;
   }
   setName(name = 'no name') {
     this.name = name;
   }
}

const MyLife = new Life();
export { getName, setName } = MyLife;
export default MyLife;

How can I use the same instance of new Life() i.e, MyLife throughout my code?

Things I have tried;

const MyLife = new Life();
export const getName = MyLife.getName.bind(MyLife);
export const setName = MyLife.setName.bind(MyLife);
export default MyLife;

Every time I try to use this in another file i.e, myOther.js

import { setName } from '../path-of-class.js` setName('Luke Skywalker'); // I get undefined.

What am I doing wrong here?

P.S: the class is in another library, I compile it with webpack & then use in another <package>, The class above works fine if used locally within the same <package> but when I try to use from <package-a> to <package-b> I get setName of undefined.

Idk for sure if there is a difference but have you tried export default new Life(); instead of all bindings and then importing ìmport life from '../Life'; — jank
– jank, Commented Jul 10, 2019 at 10:27
I want to be able use getName & setName of the same instance from one place. — Adeel Imran
– Adeel Imran, Commented Jul 10, 2019 at 12:36

RayWiis · Accepted Answer · 2019-07-10 14:02:46Z

1

Try saving your instance of Life into a static variable probably near the class and return it with a static method

class Life {
   static getInstance() {
     if (!Life.instance) {
       Life.instance = new Life();
     }
     return Life.instance;

   }
   constructor(name = 'no name') {
     this.name = name;
   }
   getName() {
     return this.name;
   }
   setName(name = 'no name') {
     this.name = name;
   }
}

Life.instance = null;

export default Life;

in another file:

import Life from 'module';
const myLife = Life.getInstance();

I'm not completely certain how webpack handles the imports. But having a single instance of a class and using it everywhere is a common pattern in object oriented programming (lookup singleton), usually solved by attaching a static variable of the instance to a class and getting it with a static method. This example achieves the same thing by having a static instance and using getInstance() to return it or create one if it wasn't already. This is a classic implementation of this pattern.

edited Jul 10, 2019 at 14:02

answered Jul 10, 2019 at 10:10

RayWiis

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1 Comment

Adeel Imran Over a year ago

Can you please explain your code a bit more, as to how it solved the problem & what it is trying to achieve here. =)

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