How to Implement the Singleton Pattern in JavaScript?

How to Create a Singleton in JavaScript

In JavaScript, a singleton pattern ensures that only one instance of a class or object can be created. The simplest way to implement a singleton is through an object literal:

var myInstance = {
  method1: function () {
    // ...
  },
  method2: function () {
    // ...
  }
};

For private members, use a function expression:

var myInstance = (function() {
  var privateVar = '';

  function privateMethod () {
    // ...
  }

  return { // public interface
    publicMethod1: function () {
      // All private members are accessible here
    },
    publicMethod2: function () {
    }
  };
})();

This pattern, known as the module pattern, encapsulates private members through closures.

To prevent modifications, use Object.freeze:

Object.freeze(myInstance);

In ES6, use ES Modules:

// my-singleton.js
const somePrivateState = []

function privateFn () {
  // ...
}

export default {
  method1() {
    // ...
  },
  method2() {
    // ...
  }
}

Then import it:

import myInstance from './my-singleton.js'
// ...

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