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Singleton Pattern in JavaScript

Artem on April 12, 2020

If you come from Java or C++ background, you are probably used to classic OOP model, and it is hard to imagine how you can implement singleton in J...

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Andrew Rothman • Apr 13 '20 • Edited

This can also be done in ES6 like so:

import axios from "axios";

class Http {
    static get(url) {
        return axios.get(url);
    }

    static post(url) {
        return axios.post(url);
    }
}

Artem • Apr 13 '20

Yes, this is another way of doing it.

Maximilian Burszley • Apr 13 '20

Not sure this is a Singleton at all, just an immutable instance due to a closure creating pseudo-private members.

A Singleton indicates you can only ever have one instance of an object. Every new Http(args) would be a reference to the same thing.

Artem • Apr 13 '20

This assumption is correct. That said, you should not use new keyword with this pattern. You can add a function to explicitly initialize singleton, and it would look more like traditional "Java" singleton. I don't think the latter is necessary though.

sanderdebr • Apr 13 '20

Good article! I reproduced it using ES6 modules:

Artem • Apr 13 '20

Cool! Glad you like it, and thanks for ES6 example!

Alex Gower • Apr 13 '20

Can you explain this to a 5 year old?

Artem • Apr 13 '20

If the 5 year old already has some experience with programming, then it may work:
One way to implement singleton pattern in JS, is to encapsulate (enclose) desired members into outer function, but provide reference to desired properties of these members using inner function (same scope as the members). We can then immediately execute (invoke) inner function, and assign the value to a variable in a global scope (or different scope depending on use).