Javascript Design Patterns #2 - Singleton Pattern

What is the Singleton design pattern?
The Singleton pattern allows you to limit the number of instances of a particular object to one. This single instance is called the singleton. Singletons reduce the need for global variables which is particularly important in JavaScript because it limits namespace pollution and associated risk of name collisions.

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[stevekingu]

Honestly I used to get confused with this 'design pattern' thing, but after watching your series I'm like "Oh, so this is it!" ...Thanks to you bro and stay blessed

[neuodev]

The is "single" video I need to watch to undertand the "Singleton" pattern :)

[O_Eduardo]

Nice video... I think that most of design patterns needs to be repaginated when we are in the javascript context. Most of the cases the language can solve some sort of problems in a more simpler way. In the singleton example, you can just export a object with all the required methods in it, and then you can import at any level, on any component because the js module system will not load it twice, so you won't have 2 instances of the same module.

If you don't want that kind of behavior, you can use a factory, so instead of exporting an object with methods within, you can export a function so you have to call it in order to get a new instance of something.

[ayush]

Wow sir.. you truly showed the power of IIFE. Never seen such a beautiful example on IIFE and on Singleton as well.. Kudos!

[aztracker]

Should probably update this... if you are using either commonjs (node-style) or esm/mjs (module) patterns, you can simply have your variable, constructor/class and export the method to retrieve or instantiate the singleton...

[bhanuprathap]

Very good example and simplified explanation.

[rutwickgangurde]

You should use parantheses even for a single line if statement, at least in videos like these. Because the readability is low in videos so its easy to think that the return belongs to the if.

[ram-gbxg]

Great way of explaining, thank you so much!

[dmytromahas]

Reminds me a lazy loading approach, but with instance initialization instead of actual loading

[RahulKumar-fzcg]

In this example where you have used Process constructor ? Just created and not used ? I got confused due to that.

[StaceyWilsonlosangeles]

Quick Question: Are you dropping down the first bracket intentionally or is this because you are using JSbin. Also, I have noticed that you are not closing out your statements with a semi-colon. Overall, I enjoy your videos because you cover more advanced topcis. Great Job!!!

[faultfinderx]

First of all I appreciate the work you've done, the explanation is great! Thx!
But you've written useless lines of code.
As you reassign pManager twice.
It's simply should be:

const Singleton = (function(){
let pManager

function ProcessManager() { /*...*/ }

return {
getProcessManager: () =>
{
if(!pManager)
pManager = new ProcessManager()
return pManager
}
}
})()

P.S. Adding line numeratorion in your code editor would help to discuss example as well

[tahasaleh]

Again, Great video! But a quick question, in "getProcessManager()" isn't reassigning "pManager = createProcessManager()" redundant, and simply calling "createProcessManager()" will do the job?

[javascriptduniya]

function Process(state) not used ? is there any value for just defining it here ?

[Erliortmejurur]

Not a critical question, just wondering - why are you using PascalCase here?

[mattsmith]

I'm working with a "black box" of APIs and want everyone's opinion.
Should I should use this pattern instead of using global variables? I have limited options.

[ultimatewarriorfrieza]

I'm finding it difficult to understand Singleton. But from my understanding, the same below could already served the purpose.

const x = {}

function Singleton(){
return x;
}

module.exports = Singleton;


* invoking new or calling the Singleton() itself will just return the same object. So singleton, isn't that right? After all, why bother with al the complexity when we could all understand it this way

[joaomendoncayt]

Sage.. I feel like I'm using Singleton way too much.. Basicly everytime I have a class with some kind of "state" I always make it a Singleton because I want to access the same data instance everywhere.

Does this sound like bad design/arquitecture or is this common to happen?

[samdimahmood]

why did we use an IIFE for the Singleton Function?

[kachunchan]

Why does the if statement returns true for the 2nd time, how does javascript knows pManager exists on the second invocation?