Object-Oriented JavaScript — Singletons and Decorators

Object-Oriented JavaScript — Singletons and Decorators

2 simple design patterns to follow.

JavaScript is partly an object-oriented language.

To learn JavaScript, we got to learn the object-oriented parts of JavaScript.

In this article, we’ll look at some basic design patterns.

Class-Like Singleton

We can create a singleton object by storing the class instance in a global object.

For instance, we can write:

function Foo() {
  if (typeof globalFoo === "undefined") {
    globalFoo = this;
  }
  return globalFoo;
}

then we can create a Foo instance by writing:

const a = new Foo();
const b = new Foo();
console.log(a === b);

And the console log should log true since we store the existing instance in a global variable.

Then we returned it if it’s not undefined .

Singleton Stored in the Property of the Constructor

We know we shouldn’t use global variables, so we can store the singleton instance as a property of the constructor instead.

Functions can have properties since they are objects.

So we can write:

function Foo() {
  if (typeof Foo.instance === "undefined") {
    Foo.instance = this;
  }
  return Foo.instance;
}

The only change is that we store the property in the instance instead of in a global variable.

We can also store it in a private property if we put it in a function.

So we can write:

const Foo = (() => {
  let instance;
  return function() {
    if (typeof instance === "undefined") {
      instance = this;
    }
    return instance;
  }
})();

and do the same thing.

This way, we can’t accidentally change the instance to something else.

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