How to import objects in Javascript/node

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05-09-2024

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Mastering Object Imports in JavaScript/Node.js: Avoiding Shared State and Ensuring Independence

In JavaScript, especially when working with Node.js, the way you import and utilize objects plays a crucial role in how your code behaves. This article explores the nuances of object importing, focusing on preventing unintended shared states and ensuring individual instances. Let's dive into the concepts and provide practical solutions.

Understanding the Issue: Shared State

The provided code illustrates a common pitfall: shared state between different parts of your application. When you use require('./main2').obj, you're effectively importing the same single instance of the obj object into both abc.js and def.js. This means any modification made to obj in abc.js (e.g., setting x to 50) will be reflected in def.js, resulting in unexpected outcomes.

Solutions for Independent Instances

The key is to ensure that each file works with its own instance of obj. Here are two proven approaches:

1. Using a Factory Function:

// main2.js
function createObj() {
  return {
    x: 10,
    setX: function (y) {
      this.x = y;
    },
    getX: function () {
      return this.x;
    }
  };
}

module.exports = { createObj }; // Export the factory function

// abc.js
const { createObj } = require('./main2');
const obj = createObj();

describe('Test', function () {
  it('Set X', () => {
    obj.setX(50);
  });
});

// def.js
const { createObj } = require('./main2');
const obj = createObj();

describe('Test', function () {
  it('Get X', () => {
    console.log(obj.getX()); // Output: 10
  });
});

Explanation:

• createObj is now a factory function that creates and returns a new instance of the obj object every time it's called.
• By calling createObj() in both abc.js and def.js, we guarantee that each file operates on its own independent instance, ensuring that the x value remains at 10 in def.js.

2. Using a Class (ES6+):

// main2.js
class MyObject {
  constructor() {
    this.x = 10;
  }

  setX(y) {
    this.x = y;
  }

  getX() {
    return this.x;
  }
}

module.exports = { MyObject }; // Export the class

// abc.js
const { MyObject } = require('./main2');
const obj = new MyObject();

describe('Test', function () {
  it('Set X', () => {
    obj.setX(50);
  });
});

// def.js
const { MyObject } = require('./main2');
const obj = new MyObject();

describe('Test', function () {
  it('Get X', () => {
    console.log(obj.getX()); // Output: 10
  });
});

Explanation:

• MyObject is defined as a class, providing a blueprint for creating objects.
• Each file uses new MyObject() to instantiate a new object, again ensuring isolation.

Additional Considerations:

• Object Pooling: If you're working with resource-intensive objects, consider using object pooling to reuse instances and reduce creation overhead. Libraries like node-object-pool can help.
• Dependency Injection: For larger projects, use dependency injection frameworks like inversify to manage object creation and dependencies gracefully.

Key Takeaway:

Understanding how object imports work in JavaScript/Node.js is crucial for building reliable and predictable applications. Avoid shared state issues by employing factory functions or classes, ensuring that each part of your code operates with independent object instances. By doing so, you'll maintain code integrity and prevent unexpected side effects, leading to more robust and scalable applications.

Attribution:

• Original Stack Overflow Question: https://stackoverflow.com/questions/21579910/javascript-require-file-creates-shared-object-across-different-files