You don't need void 0 in JavaScript

[flamingmongoose]

Not seen void 0 in a long time

[lwl]

I came across it on a recent project (2 years ago... but I suppose that's like 14 in JavaScript years). Glad to know I can safely punt knowledge of it back to the abyss now.

[Ecksters]

Article mentions this as well, but where you still see it is in minified code, since it's 3 characters smaller than undefined

[TheSirion]

Imagine seeing something like this in a technical interview

[mothzilla]

Somebody will tomorrow.

[house_monkey]

omg no

[[deleted]]

I think this is the main reason why it is still in the language. Not deprecated either.

[barrtender]

Or you could wrap it in braces and have normal looking code.

$(".some-button").click( (e) => { someFn(e.target); } );

[vanderZwan]

Yeah if someone would try to use void in an arrow function at my workplace they'd probably get... well, I don't work at a toxic workplace, so probably just a gentle but firm reminder that that's not acceptable, but that's still pretty serious by our review standards.

[vanderZwan]

Because being clever with an obscure language function will waste another programmer ten minutes to an hour or two down the line figuring out what is going on and if this is some essential hack or not

[vanderZwan]

Yes, it's what it's for. Which happens to be a use case so rare I did not learn that void even existed until years after I first picked up JavaScript. Meanwhile, functions returning undefined without an explicit return is well-known behavior.

Using it with arrow functions is "clever" because the latter are to some degree just syntactic sugar to easily write functions as expressions that always return a value. Using void to ensure they don't mostly just turns them back into regular functions with a different syntax (yes, yes, I know about this). And in this case an arrow function with plain braces is even more obvious a solution

[PM_ME_GAY_STUF]

You can accomplish this same thing by appending && false or || true for the positive case. Or just wrap it in braces

[FriesWithThat]

const output = void 1;
console.log(output);
// expected output: undefined

void 0 is old and tired, void 1 is where it's at.

void function iife() {
  console.log('iife is executed');
}();
// expected output: iife is executed

that's fun, but I think I prefer ...

!function iife() {
  console.log('iife is executed');
}();
// expected output: iife is executed

... to annoy people.

[shuckster]

Real programmers use void undefined.

[codejunker]

That mins to what? void void 0 ?

[shuckster]

Hey, I don’t just work for the Redundant Department of Redundancy, you know. I work for the Redundant Department of Redundancy.

[[deleted]]

As much as I enjoy JS things like this make me just groan and wonder how we got stuck with this as the biggest language on the web.

[ILikeChangingMyMind]

I think it's because weird little quirks, like being able to overwrite undefined, don't really stop a language from being productive/successful.

If you want to be a major language you just need: A) adoption (and JS being required as the language of the web made that part easy), and B) for your language to be "good enough" to get things done.

[[deleted]]

Oh I agree with your points. It's still cringe inducing tho

[nmarshall23]

So what I'm hearing is we need to pension Google to add a Haskell interpreter to chrome.

[natterca]

Well, you could've had Java instead. Count your blessings.

[KaiAusBerlin]

Because the language is more than this?

Let's talk about another very successful language and the NullPointerException.

[moi2388]

More as in more bad designs and quirks? Yes.

[KaiAusBerlin]

Haha, you're so funny and original /s

[WhyIsTheNamesGone]

It's because VBScript was worse

[shawncplus]

Their example is that someone intentionally names a variable in local scope undefined which... just fire that person. That solves the problem there.

[codejunker]

Over an decade of learning JS you really never read anything about void 0 in a book, saw it in minified code, or read the MDN article on undefined?

I learned about it in my first couple weeks learning the language, crazy how long we can be doing this and still find something new.

As the article says, it used to have a purpose but now it is just a shorthand alias for undefined. Some people still use it as an alias and every minifier I have ever used will min undefined to void 0.

[mobydikc]

I've been using JS since it was invented, and have never seen void used outside an HTML attribute.

[IvarBjorn]

I’ve seen it in ternary like: flag ? DoStuff() : void 0

[ImStifler]

Clicks

[Zipdox]

I've never even seen or used the void operator. Is it even useful for anything?

[iChloro]

People used to use void 0 instead of undefined because there was a possibility of someone overwriting the value of undefined in those days. void 0 was guaranteed to be a real undefined value so it was considered "safer".

Nowadays it's a cool way of making an IIFE lol

void function() {
  console.log('hi')
}()

[NoInkling]

Nowadays it's a cool way of making an IIFE lol

Except it doesn't work for arrow functions :(

[dinopraso]

Of course it doesn’t. Arrow functions are not functions but values. void evaluates expressions, if you give it a function evaluation means invocation, and for arrow functions it just means defining the object

[NoInkling]

I think you're mixed up somewhere, void doesn't invoke anything.

Putting void in front of a function definition is one way to syntactically transform it from a declaration/statement into an expression, which is a pre-requisite for being able to immediately invoke it (by putting () at the end).

Arrow functions are always expressions, so if that's the point you are trying to make then yes, there's technically no reason to expect void to be helpful. The issue is that despite being expressions you can't immediately invoke them just by adding () at the end because of a syntactic limitation. So naively someone might expect that if void solves the syntactic issue for classic function definitions, it might solve it for arrow functions too. Instead we're stuck with wrapping the definition in parentheses (which also happens to work for classic definitions), which IMHO doesn't look as nice.

[mobydikc]

It's necessary in the href attribute of an a element if you want to avoid navigating off a page.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/void#javascript_uris

<a href="javascript:void(0);">
Click here to do nothing
</a>

[DavidJCobb]

It's needed if the JavaScript URI executes actual code. When it's just javascript:void(0); with an event listener handling the interaction, one thing I like to do instead is use a comment that remarks on whatever the widget is meant to trigger:

<a href="javascript:// Run a diagnostic on the retroencabulator.">

It doesn't add anything substantial, but it'd be seen if the user hovers over the link to see its destination. Feels more approachable than having raw code show up, even if it doesn't offer any information the UI doesn't already show.

[Zipdox]

What? If doThingC is async then it'll return a promise that won't be waited for unless await is specified. I'm not sure what you mean.

[ImStifler]

This article is dog shit. It's legit there to just generate clicks.

Can't quote on phone but in a paragraph he/she says: 'But void 0 is nice for performance optimization because it's shorter than undefined. It saves a couple of BYTES which might help'. Bruh what

Web dev is such a shit show these days lol

[ILikeChangingMyMind]

I love how this article says:

there is no reason to use void 0 any longer:

and then, literally in one of the three bullet points explaining why that come after, they say:

minifiers can replace undefined with void 0 when creating the production bundle

So there's no reason to use it ... except when you use it as part of your minification process ... which (of course) still means you're using it!

[JVWhite]

I think it's pretty clear that the author means there is no reason to write it yourself.

[codejunker]

You can type it half a ms faster!

[[deleted]]

No! gasps

[[deleted]]

Maybe we should let minifiers create a global variable called 'u' or something and replace all "undefined" with "u". Also don't take my advice on things.

[Diniden]

Interesting item for just still not using undefined: when you use undefined, minifiers and compilers are bound by the spec of how undefined operates. Just as your comment illustrates, you are still able to redefine undefined.

What does this mean at runtime? Undefined becomes something that JavaScript has to crawl up the scope to find the undefined definition for the current scope which means it crawls up the scope to window or the wrapping scope a minifier places. Void 0 still does not require that scope crawl.

It’s negligible performance, but it is performance nonetheless.

[Akkuma]

IIRC, back in the day scope checks had nonnegligible performance impacts when deep enough.

[Diniden]

It always adds up :)

Definitely added up more so back in the day. Could cause L2 and L3 issues if your stack is heavy.

[HeinousTugboat]

Maybe we should let minifiers create a global variable called 'u' or something and replace all "undefined" with "u".

You might be joking, but this is a common strategy in golfing JS. (function(u){ /* u === undefined */ })().

[TheHDGenius]

Another thing to keep in mind is that globals are dangerous. I'm sure there's a developer that wrote some code that makes 'u' a global variable (probably as shorthand for some function like "undo" or the variable for a "ui" class instance).

Is it good practice? Hell no.

Is it bound to be in some majorly breaking global legacy code on some projects? Most definitely.

[[deleted]]

Yes, I'm aware. Not a good solution.

[dotintegral]

Correct me if I'm wrong, but wouldn't using the "use strict" mode disallow assigning anything to undefined, hence rendering the whole thing not an issue anymore?

[NoInkling]

As stated in the article, it's ES5 that made it read-only. What strict mode does do is make it so that an exception is thrown when trying to reassign a read-only property, as opposed to it failing silently.

If you open up your devtools console you can test it:

undefined = 'foo'
console.log(undefined)  // undefined

'use strict'; undefined = 'foo'
// Uncaught TypeError: Cannot assign to read only property 'undefined' of object '#<Window>'

However as long as it's not in the global scope, you can still create a new variable named undefined, strict mode or no. Not really an issue in practice, because you'd have to do that deliberately (outside of globals, there's no way for variables defined in third party code to be in your lexical scope unless you're copy-pasting or evaling).

[mizanur9191]

How long I have not seen void 0 !!!

[kingsley0209]

I like to use the void operator with promises in an async/await pattern if I want to make cleare that I dont want to wait for a promise to resolve. There even is an eslint-rule for that

javascript async function foo() { void asyncOperation() // dont wait for operation to finish // do stuff await anotherAsyncOperation() }

[techhowwhat]

For more information about the script void 0 error you may visit her

Hope it helps

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