Yes but that’s an anti pattern. Arrow functions aren’t there to look cool, they’re how you define lambdas / anonymous functions.

Other than that, functions should be defined by the keyword.

How is that an anti-pattern?

> Other than that, functions should be defined by the keyword.

Says who?

Anonymous functions don't have names. This makes it much harder to do things like profiling (just try to find that one specific arrow function in your performance profile flame graph) and tracing. Tools like Sentry that automatically log stack traces when errors occur become much less useful if every function is anonymous.

    const foo = () => {}

This function is not anonymous, it's called foo.

Interesting, it seems that the javascript runtime is smart enough detect this pattern and actually create a named function (I tried Chrome and Node.js)

    const foo = () => {}
    console.log( foo.name );

actually outputs 'foo', and not the empty string that I was expecting.

   const test = () => ( () => {} );
   const foo = test();
   console.log( foo.name );

outputs the empty string.

Is this behavior required by the standard ?

Yes, in great detail. https://tc39.es/ecma262/multipage/ordinary-and-exotic-object... is the specification, and for the TL;DR https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... is pretty good.

You're probably remembering how it used to work. This is the example I remember from way back that we shouldn't use because (aside from being unnecessary and weird) this function wouldn't have a name in stack traces:

  var foo = function() {};

Except nowadays it too does have the name "foo".

But to call foo in bar you must define foo before bar.

function foo(){} is also callable if bar is defined before foo.

Not true at the top-level.

Not sure what you find not true about it. All named “function”s get hoisted just like “var”s, I use post-definitions of utility functions all the time in file scopes, function scopes, after return statements, everywhere. You’re probably thinking about

  const foo = function (){}

without its own name before (). These behave like expressions and cannot be hoisted.

> I use post-definitions of utility functions all the time in file scopes, function scopes, after return statements, everywhere

I haven't figured out if people consider this a best practice, but I love doing it. To me the list of called functions is a high-level explanation of the code, and listing all the definitions first just buries the high-level logic "below the fold". Immediately diving into function contents outside of their broader context is confusing to me.

I don’t monitor “best” practices, so beware. But in languages like C and Pascal I also had a habit of simply declaring all interfaces at the top and then grouping implementations reasonably. It also created a nice “index” of what’s in the file.

Hoisting also enables cross-imports without helper unit extraction headaches. Many hate js/ts at the “kids hate == and null” level but in reality these languages have a very practical design that wins so many rounds irl.

Does the function know it’s called foo for tracing/error logging/etc?

Not really, its an anonymous function stored in a variable foo

To me, arrow functions behave more like I would expect functions to behave. They don’t include all the magic bindings that the function keyword imparts. Feels more “pure” to me. Anonymous functions can be either function () {} or () => {}

As of a few years ago (not sure about now) the backtrace frame info for anonymous functions were far worse than ones defined via the function keyword with a name.

All the wise ones. Well, except for you maybe.

Serious arguments would be:

- readability

- greppability

(It wasn't an insult, but a joke on the username)

Functions and arrow functions have an important difference: arrow functions do not create their own `this`. If you're in a context where a nested function needs to maintain access to the outer function’s `this`, and you don't want to muck with `bind` or `call`, then you need an arrow function.

Am I the only one who hates arrow functions?

I did, until I used them enough where I saw where they were useful.

The bad examples of arrow functions I saw initially were of:

1. Devs trying to mix them in with OOP code as a bandaid over OOP headahes (e.g. bind/this) instead of just not using OOP in the first place.

2. Devs trying to stick functional programming everywhere because they had seen a trivial example where a `.map()` made more semantic sense than a for/for-in/for-of loop. Despite the fact that for/for-in/for-of loops were easier to read for anything non-trivial and also had better performance because you had access to the `break`, `continue` and `return` keywords.

    > also had better performance because you had access to the `break`, `continue` and `return` keywords.

This is a great point.

One more: Debugging `.map()` is also much harder than a for loop.

I feel there are a few ways to invoke .map() in a readable way and many ways that make the code flow needlessly indirect.

Should be a judgment call, and the author needs to be used to doing both looping and mapping constructs, so that they are unafraid of the bit of extra typing needed for the loop.

Another benefit of using for instead of array fns is that it is easy to add await keyword should the fn become async.

But many teams will have it as a rule to always use array fns.

That gives you have the option of making it serially async but not parallel, which can be achieved easily using Promise.all in either scenario.

As an aside: It’s way less ergonomic, but you likely want `Promise.allSettled` rather than `Promise.all` as the first promise that throws aborts the rest.

It doesn’t really abort the rest, it just prioritizes the selection of a first catch-path as a current continuation. The rest is still thenable, and there’s no “abort promise” operation in general. There are abort signals, but it’s up to an async process to accept a signal and decide when/whether to check it.

Admittedly, I was being a bit hand-wavy and describing a bit more of how it feels rather than the way it is (I'm perpetually annoyed that promises can't be cancelled), but I was thinking of the code I've seen many times across many code bases:

    let results;
    try {
      results = await Promise.all(vals.map(someAsyncOp))
    } catch (err) {
      console.error(err)
    }

While you could pull that promises mapping into a variable and keep it thenable, 99% of the time I see the above instead. Promises have some rough edges because they are stateful, so I think it might be easier to recommend swapping that Promise.all for an Promise.allSettled, and using a shared utility for parsing the promise result.

I consider this issue akin to the relationship between `sort`, `reverse`, `splice`, the mutating operation APIs, and their non mutating counterparts `toSorted`, `toReversed`, `toSpliced`. Promise.all is kind of the mutating version of allSettled.

I don't like using them everywhere, but they're very handy for inline anonymous functions.

But it really pains me when I see

export const foo = () => {}

instead of

export function foo() {}

Thank you, that's something I also never have understood myself. For inline anonymous functions like callbacks they make perfect sense. As long as you don't need `this`.

But everywhere else they reduce readability of the code with no tangible benefit I am aware of.

But do they make much of a difference? You have always been able to write:

    myArray.sort(function(a,b){return a-b})

People for some reason treat this syntactic sugar like it gives them some new fundamental ability.

Oh Javascript would be much better if it could only be syntactic sugar...

`function(a,b){return a-b;}` is different from `(a,b) => a - b`

And `function diff(a,b) {return a-b;}` is different from `const diff(a,b) => a - b;`.

I wish javascript had a built-in or at least (defacto) default linter. Like go-fmt or rust fmt. Or clippy even.

One that could enforce these styles. Because not only is the export const foo = () {}

painful on itself, it will quite certainly get intermixed with the

function foo() {}

and then in the next library a

const foo = function() {}

and so on. I'd rather have a consistently irritating style, than this willy-nilly yolo style that the JS community seems to embrace.

ESLint and Prettier are the de facto default linter/formatter combo in JS. There are rules you can enable to enforce your preferred style of function [1][2].

[1] https://eslint.org/docs/latest/rules/func-style

[2] https://eslint.org/docs/latest/rules/prefer-arrow-callback

They are miles away from `gofmt` or `rust fmt` or `cargo clippy` and so on.

It's not opinionated, but requiring you to form your own opinion or at least choose from a palette of opinions.

It requires effort to opt-in rather than effort to opt-out.

The community doesn't frown on code that's not adhering to the common standard or code that doesn't pass the "out of the box" linter.

So, if I have a typescript project with a tree of some 20 dependencies (which is, unfortunately, a tiny project), I'll have at least five styles of code when it browse through it. Some JS, some TS, some strictly linted with "no-bikeshedding", some linted with configs that are bigger than the codebase itself. Some linted with outdated. Many not linted at all. It's really a mess. Even if each of the 20 dependencies themselves are clean, beauties, the whole is an inconsistent mess.

I personally believe that Prettier strikes a decent balance between being configurable vs being opinionated. I've used formatters that are much less opinionated than Prettier (e.g. the last time I used XCode it only handled indentation by default). ESLint also teeters on the edge between configuration vs convention quite well in my opinion, especially given the fact that browser JS and server side JS have vastly different linting requirements. I also love the extensibility of ESLint. Being able to write your own linting rules is a boon on productivity. Having access to custom framework specific linting rules is quite nice (I couldn't use React without the react-hooks/rules-of-hooks third party ESLint rules).

> Some JS, some TS

I think the JS community has done remarkably well amongst dynamically typed languages in settling on one form of gradual typing and adopting it fervently (Flow no longer has any market share at all). Whereas the last time I checked Python still had the Mypy/Pywright divide, and Ruby had the Sorbet/RBS dichotomy.

Ultimately though, most of your critique boils down to the fact that JS (unlike Rust and Go) isn't maintained by a single monolithic entity, and therefore there's no one to dictate the standards you're looking for. If Deno were the sole caretaker of JS for example, we'd have a standard linter and formatter devoid of complex configuration, but Deno doesn't control JS.

This is a consequence of JS being a collaborative product of the various browser vendors, TC39, and the server side JS runtimes that have adapted JS to run on servers. The advantage of this of course though is that JS can run natively in the browser. I think that's a decent tradeoff to make in exchange for having to wade through dependencies with different ideas about when it's appropriate to use arrow functions.

These aren't equivalent as function foo will be hoisted but const foo will not be.

Sure the food that this restaurant serves is pricey, but you have to remember that it also tastes terrible.

Yep, and that usually doesn't matter at the top level.

I like them because it reinforces the idea that functions are just values like any other - having a separate keyword feels like it is inconsistent.

Moreover the binding and lexical scope aspects supported by classic functions are amongst the worst aspects of the language.

Arrow functions are also far more concise and ergonomic when working with higher order functions or simple expressions

The main thing to be wary of with arrow functions is when they are used anonymously inline without it being clear what the function is doing at a glance. That and Error stack traces but the latter is exacerbated by there being no actual standard regarding Error.prototype.stack

Why do you want to reinforce that idea?

To me arrow functions mostly just decrease readability and makes them blend in too much, when it should be important distinction what is a function and what is not.

Not to be dismissive, but because I like it - it just sits right with me.

I'm not a javascript programmer, but I really like the arrow pattern from a distance exactly because it enforces that idea.

My experience is that newcomers are often thrown off and confused by higher order functions. I think partly because, well let's be honest they just are more confusing than normal functions, but I think it's also because languages often bind functions differently from everything else.

`const cool = () => 5`

Makes it obvious and transparent, that `cool' is just a variable where as:

`function cool() {return 5}`

looks very different from other variable bindings.

Since we're on the topic of higher order functions, arrow functions allow you to express function currying very succinctly (which some people prefer). This is a contrived example to illustrate the syntactical differences:

  const arrow = (a) => (b) => `${a}-${b}`
  
  function verbose(a) {
    return function (b) {
      return `${a}-${b}`
    }
  }
  
  function uncurried(a, b) {
    return `${a}-${b}`
  }
  
  const values = ['foo', 'bar', 'baz']
  values.map(arrow('qux'))
  values.map(verbose('qux'))
  values.map(uncurried.bind(null, 'qux'))
  values.map((b) => uncurried('qux', b))

> should be important distinction what is a function and what is not

code is to express logic clearly to the reader. We should assess it for that purpose, before assess for any derivative, secondary concern such as whether categories of things in code (function etc) visually pops out when you use some specific tool like vim, or grep. There are syntax highlighters for a reason. And maybe if grep sucks with code then build the proper tool for code searching, instead of writing code after the tool.

I very much prefer the way scoping is handled in arrow functions.

A simple heuristic I use is to use arrow functions for inline function arguments, and named "function" functions for all others.

One reason is exactly what the subject of discussion is here, it's easier to string-search with that keyword in front of the name, but I don't need that for trivial inline functions (whenever I do I make it an actual function that I declare normally and not inline).

Then there's the different handling of "this", depending on how you write your code this may be an important reason to use an arrow function in some places.

I'm of the opinion that giving a global name to an anonymous function should result in a compilation error.

why the need to pronounce arbitrary preferences, who cares?

I want to talk to the developer who considers greppability when deciding whether to use the "function" keyword but requires his definitions to be greppable by distancing them from their call locations. I just have a few questions for him.

The => is after the param spec, so you’re searching for foo.*=> or something more complex, but then still missing multiline signatures. This is very easy to get caught by in TypeScript, and also happens when dealing with higher-order functions (quite common in React).

Why are you searching for foo.=>

Are you searching through every function, or functions that have a very specific parameter?

And whatever you picked, why?

---------------------------------------------------------------

- If you're searching for every function, then there's no need to search for foo.=>, you only need to search for function and =>.

- If you're searching for a specific parameter, then just search for the parameter. Searching for functions is redundant.

---------------------------------------------------------------

Arrow function expressions and function expressions can both be named or anonymous.

Introducing arrow functions didn't suddenly make JavaScript unsearchable.

JavaScript supported anonymous functions before arrow function expressions were introduced.

Anonymous functions can only ever be:

- run on the spot

- thrown away

- or passed around after they've been given a label

Which means, whenever you actually want to search for something, it's going to be labelled.

So search for the label.

You can still look for `(funcname)\s*=` can't you? I mean it's not like functions get re-declared a lot.

You can still search for `<keyword> = \(.*\) => `, albeit it's a bit cumbersome.

All you need is a tool that actually understands the language.

It's 2024 and HN still suggests using regular expressions to search through a code base.

Regex is a universal tool.

Your special tool might not work on plattform X, fails for edge case - and you generally don't know how it works. With regex or simple string search - I am in control. And can understand why results show up, or investigate when they don't, but should.

> Your special tool might not work on plattform X

As always, people come out with the weirdest of excuses to not use actual tools in the 99.9999% of the cases when they are available, and work.

When that tools doesn't work, or isn't sufficient, use another one like fuzzy text search or regexps.

> and you generally don't know how it works.

Do you know how your stove works? Or do you truly understand what the device you're typing this comment on truly works?

Only in programming I see people deliberately avoid useful tools because <some fringe edge case that comes up once in a millenium in their daily work>

if you think anything works in 99.9999% of cases, you’ve never programmed a computer

It’s you who sees it as excuses. If I have a screwdriver multitool, I don’t need another one which is for d10 only. It simply creates unnecessary clutter in a toolbox. The difference between definition and mention search for a function is:

  gr<bs><bs>ion name<cr>
  vs
  grname<cr>

or for the current identifier, simply

  gr<m-w><cr>

I could even make my own useful tools like “\[fvm]gr” for function, variable or field search and brag about it watching miserable ide guys from the high balcony, but ain’t that unnecessary as well.

> It simply creates unnecessary clutter in a toolbox.

And then you proceed to... invent several pale imitations of a symbol/usages search.

More here: https://news.ycombinator.com/item?id=41435862 so as not to repeat myself

Doesn’t really apply, ignores things just said.

When you specialize in one thing only, do what you want.

But I prefer tools, that I can use wherever I go. To not be dependant and chained to that environment.

"Do you know how your stove works? Or do you truly understand what the device you're typing this comment on truly works?"

Also yes, I do.

" people deliberately avoid useful tools because <some fringe edge case that comes up once in a millenium in their daily work>"

Well, or I did already changed tools often enough, to be fed up with it and rather invest in tech that does not loose its value in the next iteration of the innovation cycle.

> When you specialize in one thing only, do what you want.

I specialize in one thing only: programming

> But I prefer tools, that I can use wherever I go.

Do you always walk everywhere, or do you use a tool available at the time, like cars, planes, bycicles, public transport?

> rather invest in tech that does not loose its value in the next iteration of the innovation cycle.

Things like "fund symbol", "find usages", "find implementation" have been available in actual tools for close to two decades now.

I did not say I do not use what is avaiable, but this debate is about in general having your code in a shape that simply searching for strings work.

Simply searching for strings rarely works well as the codebase grows larger. Because besides knowing where all things named X are, you want to actually see where X is used, or where it's called from, or where it is defined.

With search you end up grepping the code twice:

- first grepping for the name

We're literally in a thread where people invent regexes for how to search the same thing (a function) defined in two different ways (as a function or as a const)

- secondly, manually grepping through search results deducing if it's relevant to what you're looking for

It becomes significantly worse if you want to include third-party libs in your search.

There are countless times when I would just Cmd+B/Cmd+Click a symbol in IDEA and continue my exploration down to Java's own libraries. There are next to zero cases when IDEA would fail to recognise a function and find its usages if it was defined as a const, not as a function. Why would I willingly deny myself these tools as so many in this thread do?

I both agree and disagree with this.

I was very careful about how I phrased my comment. Languages can gain points by being greppable, and they can gain points by having a well–implemented mode for my favorite editor, and they can also gain points by having a well–implemented language server. They can do all three to gain the most points (and of course there are many other ways to gain or lose points; this is just one tiny aspect of language design), but they don’t have to. And nobody should try to force every language designer to shave the yak of writing an Emacs mode or a Language Server.

And sometimes you just want to improve some random piece of software written in a language that you’ve never used before, without having to shave a bunch of yaks to get the language server installed. Sometimes all you have is grep and you’ll want to be able to use it on this weird new language.

Its current year and IDEs still can’t remember how I just transformed the snippet of code and suggest to transform the rest of the files in the same way. All they can do in “refactor” menu is only “rename” and then some extract/etc nonsense which no one uses irl.

By using regexps I have an experience that opens many doors, and the fact that they aren’t automatic could make me sad, if only these doors weren’t completely shut without that experience.

No one is stopping you from using regexps in IDEs.

And you somehow manage to undersell the rename functionality in an IDE. And I've used move/extract functionality multiple times.

I do however agree that applicable transformations (like upgrading to new syntaxes, or ways of doing stuff as languages evolve) could be applied wholesale to large chunks of code.

The thing is: In large codebase the tool may become slow or crash, in a new language you may not have such tool.. Grep is far more robust!

When tools don't work or unsuitable, you use different tools.

And yet people are obsessed with never using useful tools in the first place because they can invent scenarios when this tool doesn't work. Even if these scenarios might never actually come up in their daily work.

Not to move the goal posts too much, but when I am searching a huge Python or Java code base from IntelliJ, I use a mixture of symbol and text search. One good thing about text search, you get hits from comments.

Yup. I do, too.

I'm mostly ranting against this weird "we will never use great tools because full-text search" obsession

All you need is `<keyword> =`

Really, all you need is `<keyword>` and if the first result is a call to that function, just jump to its definition.

Exactly.

Just search the definition.

Any time that a function doesn't have a definition, it's never the target of a search anyway.