Show HN: JavaScript PubSub in 163 Bytes
(github.com)103 points by hmmokidk 4 days ago
103 points by hmmokidk 4 days 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.
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()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.
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.
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.
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 nullish coalescing assignment operator ??= has been supported across the board for 4½ years. Avoiding it will cost six more bytes.)
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).
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.
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.
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...
So why would I use this as opposed to BroadcastChannel?
Overkill if you don't want to cross between browser frames I think, and I assume you can't pass references.
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.
Of course not but it's JavaScript, why don't we pile more on top of the garbage mountain.
Thanks! Definitely going to use `new EventTarget()` in Nue. So obvious.
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).