Singletons in JavaScript and ES6

The Java way

The first one I learned and the most used design pattern during my Java days was singleton. Writing this in JavaScript is even more simpler.

export const createSingleton = (createInstance) => {
  let instance = undefined;
  return {
    getInstance: () => instance || (instance = createInstance())
  };
};

This factory requires you to pass in a no argument function that returns a new object. This object becomes the instance value. It also is lazy. Nothing is created until you reference it.

const createSecretId = () => ({ secret: () => "shhhhh" });
const secretId = createSingleton(createSecretId);
console.log(secretId.getInstance().secret());

if you want to be truly semantic, you can use JavaScript generators instead.

const createSingleton = function*(createInstance) {
  let instance = undefined;
  yield {
    getInstance: () => instance || (instance = createInstance())
  };
};

The ES6 Way — modules

ES6 Modules are singletons. Thus all you have to do is define your object in a module. To test, you can try:

const phrase = `${Math.random()} shhh`;
export const secret = () => phrase;

Any file you import secret, you are guaranteed to receive the same value. Math.random() is there to tell you if a new value is computed each time.

Code Sandbox: https://codesandbox.io/s/es6-singletons-gwrv3