alt.hn

3/31/2025 at 1:37:55 AM

Show HN: JavaScript PubSub in 163 Bytes

 https://github.com/hassanshaikley/pico-pubsub

by hmmokidk

4/1/2025 at 10:39:13 AM

The API feels wrong. The object that was passed to pub() is the object that should be received by the callback passed to sub().

The use of EventTarget/CustomEvent is an implementation detail; it should not be part of the API.

As a result, every callback implementation is larger because it must explicitly unwrap the CustomEvent object.

Essentially, the author made the library smaller by pushing necessary code to unwrap the CustomEvent object to the callsites. That's the opposite of what good libraries do!

The mentioned nano-pubsub gets this right, and it even gets the types correct (which the posted code doesn't even try).

by sltkr

4/1/2025 at 5:34:33 PM

The point of this exercise, to my mind, is to show the utter simplicity of pub-sub. Such code belongs to the API documentation, like the code snippets on MDN.

Proper code would have expressive parameter names, good doc comments, types (TS FTW) and the niceties like unpacking you mention. One of them would be named topics mapped to EventTargets, so that publishers and subscribers won't need to have visibility into this implementation detail.

by nine_k

4/1/2025 at 3:09:50 PM

I disagree with the first point, and agree with the second.

The usage, to me, feels appropriate for JS.

I agree that event.detail should be returned instead of the whole event. Can definitely save some space at the callsites there!

by hmmokidk

4/1/2025 at 3:42:37 PM

In similar spirit, a minimal implemention of KV store, in 22 bytes:

  export default new Map

by zeroq

4/1/2025 at 11:53:04 AM

I'm not a huge fan of using CustomEvent for this.. esp. in terms of interoperability (which for these <kb challenges probably doesnt matter)

personally, i'll just roll with something like this which also is typed etc:

    export function createPubSub<T extends readonly any[]>() {
      const l = new Set<(...args: T) => void>()

      return {
        pub: (...args: T) => l.forEach((f) => f(...args)),
        sub: (f: (...args: T) => void) => l.add(f) && (() => l.delete(f)),
      }
    }

    // usage:
    const greetings = createPubSub<[string]>()
    const unsubscribe = greetings.sub((name) => {
      console.log('hi there', name)
    })
    greetings.pub('Dudeman')
    unsubscribe()

by arnorhs

4/1/2025 at 12:56:08 PM

If listeners of this implementation aren’t unsubscribed they can’t be garbage collected, and in a real world codebase that means memory leaks are inevitable. EventDispatcher has weak refs to its listeners, so it doesn’t have this problem.

by Joeri

4/1/2025 at 7:32:39 PM

The listeners can be garbage-collected if the `greetings` publisher object and any unsubscribe callbacks are garbage-collectable. This is consistent with normal Javascript EventTargets which don't use weak refs.

If only weak refs were kept to listeners, then any listeners you don't plan to unsubscribe and don't keep that callback around will effectively auto-unsubscribe themselves. If this was done and you called `greetings.sub((name) => console.log("hi there", name));` to greet every published value, then published values will stop being greeted whenever a garbage collection happens.

by AgentME

4/2/2025 at 2:21:54 PM

This is correct.

The subscribers are unlikely to be garbage collected with a weak ref as long as something else is pointing to the subscriber, so it would be a viable alternative to manual unsubscriptions - but personally I prefer to give explicit lifecycle controls to the subscriber, if possible.

by arnorhs

4/3/2025 at 2:31:28 AM

If the listener is a fresh function passed straight to the listen method as in my example, nothing else will have a reference to it besides the event target, and if that's a weak reference then it will get collected eventually and effectively unsubscribed on its own. Weak references don't make sense at all to use for general event listeners like this.

by AgentME

4/2/2025 at 2:26:50 AM

Using the event dispatch mechanism is flat-out bigger, anyway. Here’s the interface of the original script (that is, global pub/sub functions taking a name), except that the receiver site no longer needs to look at the .detail property so it’s better:

  let t={};
  sub=(e,c)=>((e=t[e]??=new Set).add(c),()=>e.delete(c));
  pub=(n,d)=>t[n]?.forEach(f=>f(d))
The original was 149 bytes; this is 97.

(The nullish coalescing assignment operator ??= has been supported across the board for 4½ years. Avoiding it will cost six more bytes.)

by chrismorgan

4/2/2025 at 3:31:40 AM

This isn't the same though. With EventTarget, if one of the callback throws, the later callbacks would still get called. With yours the later callbacks don't get called.

by ftigis

4/2/2025 at 4:13:46 AM

True, I forgot about that. Habit of working in Rust, perhaps, and generally avoiding exceptions when working in JavaScript.

Well then, a few alternatives to replace f=>f(d), each with slightly different semantics:

• async f=>f(d) (+6, 103 bytes).

• f=>{try{f(d)}catch{}} (+14, 111 bytes).

• f=>setTimeout(()=>f(d)) (+16 bytes, 113 bytes).

• f=>queueMicrotask(()=>f(d)) (+20 bytes, 117 bytes).

by chrismorgan

4/2/2025 at 3:36:05 AM

if one listener throws it will break the entire channel

by nsonha

4/1/2025 at 8:31:36 AM

TIL CustomEvent

https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent...

by est

4/1/2025 at 1:52:13 PM

Incredibly useful, especially with React, where the Context API, state lifting, and prop drilling often feel clunky. That said, it can lead to messy code if not carefully managed.

by bodantogat

4/1/2025 at 3:45:18 PM

Bingo! Having tons of `CustomEvents` with arbitrary handlers gets unwieldy. One way we "solved" this is by only allowing custom events in a `events.ts` file and document them pretty extensively.

by jilles

4/1/2025 at 10:26:03 AM

Perhaps "eventlistener" word can be extracted, and dynamically called as string to reduce bytes

by test1072

4/2/2025 at 2:12:08 AM

This has been a popular technique at times, but it tends to increase compressed sizes: gzip and similar are better at common string deduplication, having lower overhead. Such shenanigans are also bad for performance, especially in hot paths due to making it harder for the browser to optimise it.

by chrismorgan

4/1/2025 at 3:53:29 PM

You joke, but I think about things like this...a lot.

by hmmokidk

4/1/2025 at 7:05:11 PM

good to know pub-sub shenanigans are ubiquitous lol

here's my implementation from a while back with `setTimeout` like semantics; used it to avoid prop-drilling in an internal dashboard (sue me)

https://gist.github.com/thewisenerd/768db2a0046ca716e28ff14b...

by thewisenerd

4/2/2025 at 6:57:02 AM 

    sub => ref = 0
    sub => ref = 1
    unsub(0)
    sub => ref = 1 (two subs with same ref!)

by tubs

4/1/2025 at 1:56:24 PM

So why would I use this as opposed to BroadcastChannel?

by giancarlostoro

4/1/2025 at 2:14:54 PM

Overkill if you don't want to cross between browser frames I think, and I assume you can't pass references.

by ChocolateGod

4/1/2025 at 9:12:25 AM

is this like left-pad but for EventTarget? If being small is the PRIMARY goal, then we are already able to do it without a wrapper.

by nsonha

4/1/2025 at 12:17:36 PM

I think that's the (tounge in cheek) point being made

by singpolyma3

4/1/2025 at 8:57:23 AM

This is local pubsub within an application, right? i.e. corresponding to C#'s 'event' keyword.

by pjc50

4/1/2025 at 9:16:25 AM

sure if you remove the whole native package it's small

by h1fra

3/31/2025 at 8:19:41 AM

should this copy paste macro even be a package lol

by lerp-io

3/31/2025 at 10:18:10 AM

In the author's defense they do write the entire source code in README.md, including source for alternatives.

by hu3

3/31/2025 at 9:56:06 AM

Of course not but it's JavaScript, why don't we pile more on top of the garbage mountain.

by nesarkvechnep

4/1/2025 at 8:22:52 AM

Not expert enough in pub/sub to tell whether these are sufficient, but perhaps these two functions could be folded into built-ins?

by kreetx

4/1/2025 at 5:42:10 PM

[dead]

by curtisszmania

4/1/2025 at 8:53:32 AM

[flagged]

by RazorDev

4/1/2025 at 11:13:54 AM

Surely this comment was generated by an LLM?

by sltkr

4/1/2025 at 2:18:12 PM

Thanks! Definitely going to use `new EventTarget()` in Nue. So obvious.

https://nuejs.org/

by tipiirai

4/1/2025 at 9:49:54 AM

23 byte version:

    // Lib code>>
    s={};call=(n)=>{s[n]()}
    // <<

    s.hello=()=>console.log('hello');
    call('hello');
    delete s.hello;

by blatantly

4/1/2025 at 9:57:25 AM

This is missing the subscription feature?

Multiple independent listeners should be able to attach a callback that fires when “hello” is called.

by pavlov