Hacker News

by Ryan Harman

Show HN: JavaScript PubSub in 163 Bytes (github.com)

100 points by hmmokidk 3 days ago

sltkr a day ago

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).

nine_k a day ago

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.

hmmokidk a day ago

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!

zeroq a day ago

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

  export default new Map

arnorhs a day ago

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()

Joeri a day ago

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.

AgentME a day ago

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.

arnorhs 3 hours ago

chrismorgan 15 hours ago

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.)

ftigis 14 hours ago

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.

chrismorgan 13 hours ago

nsonha 13 hours ago

if one listener throws it will break the entire channel

est a day ago

TIL CustomEvent

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

bodantogat a day ago

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.

jilles a day ago

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.

test1072 a day ago

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

chrismorgan 15 hours ago

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.

hmmokidk a day ago

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

thewisenerd a day ago

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...

tubs 10 hours ago 

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

giancarlostoro a day ago

So why would I use this as opposed to BroadcastChannel?

ChocolateGod a day ago

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

pjc50 a day ago

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

diggan a day ago

It seems like it yeah. I did something that looks similar at a surface-level (https://github.com/victorb/LightYearJS/blob/master/test/acce...) around 11 years ago, but apparently called it an "Event Dispatcher", something that might fit the submission project better.

h1fra a day ago

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

nsonha a day ago

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.

singpolyma3 a day ago

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

lerp-io 2 days ago

should this copy paste macro even be a package lol

hu3 2 days ago

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

nesarkvechnep 2 days ago

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

kreetx a day ago

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

tipiirai a day ago

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

https://nuejs.org/

blatantly a day ago

23 byte version:

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

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

pavlov a day ago

This is missing the subscription feature?

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