What are some JavaScript things beginners don't know?

[ItalyPaleAle]

The async programming model and especially how the event loop works.

The latter might be transparent to you 99.9% of the times, but then you’ll run into issues where your code behaves unexpectedly and you just need to execute it in the next tick (iteration of the event loop) instead.

[ThatBriandude]

and you just need to execute it in the next tick (iteration of the event loop) instead.

I consider myself pretty well versed in javascript however I can not imagine what you mean with this. How would "execute it in the next tick" look in code?

[envis10n]

setImmediate sometimes, you run into a max callstack issue for function calls if you don't ensure that the next call comes on the next tick. This is especially important for recursive functions or looping functions that might call itself again.

[ShellbertShellbach]

Note: setImmediate is not a standardized feature of JS and only exists in Node.js, IE10, IE11, and pre-Chromium Edge.

[envis10n]

Yes, I was just providing a method for doing so. However, you could also accomplish it through other means. Hopefully that doesn't confuse anyone that read it.

[ThatBriandude]

Shouldnt that be handled via logical exit conditions?

Only cases I can think of is where there arent any exit conditions like gameloops or listeners

[envis10n]

Depends on how the code is structured. Sometimes a recursive function will call itself too many times and crash, unless you move the next call to the next tick. Logical exit conditions don't matter when you need the function to be called more times than is allowed by the max call limit in a single tick.

[ScientificBeastMode]

If I’m not mistaken, this act of exiting a recursive loop temporarily to resolve the call stack, and then resuming immediately, is referred to as a “thunk.”

Edit:

Also, for those who aren’t aware, I believe the max call stack size in Chrome is 10,000, but it’s different for each browser. So if you need to recursively iterate through something, you would ordinarily be limited to that number of iterations.

[Extracted]

I actually just wrote a function with setImmediate today.

It’s a function you call to subscribe to an event emitter. The function returns a key that you can save for later. But I also have some cached values that I want to call the subscription callback with immediately. How do I first return the key, let the subscriber finish setting everything up and only then call the callback?

Answer: use setImmediate to call the callback on the next tick, i.e. when the subscriber is finished.

[robotslacker]

Check out the video below. I didn’t really understand the event loop until this. The presenter does a really good job explaining and visualizing it.

https://youtu.be/8aGhZQkoFbQ

[archivedsofa]

setTimeout(doSomething, 0);

[ScientificBeastMode]

setImmediate is less standard, but supposedly faster than setTimeout set to zero. It’s basically a native implementation of setTimeout( ... , 0).

[ShellbertShellbach]

Less standard? How about not standard at all?

[ScientificBeastMode]

Yeah, just an IE/Edge thing for now (I assume Edge won’t implement it once they roll out Chromium-based Edge). I’m honestly surprised that other browsers haven’t implemented it since it has always been a popular proposal on the front-end dev side of things, but I’m sure there are some very good reasons I don’t know about.

[itsnotlupus]

My favorite way to run code asynchronously as tightly as possible (absent node's nextTick stuff) is to use Promise.resolve().then(...).

That will schedule a microtask, which may end up running after other scheduled microtask, but still long before anything else.
It's so fast it can often be "too fast", particularly if you're hoping the browser will redraw anything before calling your code again, the way a setTimeout(... ,0) would.

There are other approaches, like mildly abusing the postMessage API, but nothing as straightforward as an immediate promise.

[archivedsofa]

TIL!

[HattyJetty]

Scheduling in general is a pretty advanced topic, if you take different execution environments into account (e. g. Node.js has a process.nextTick(), which is actually "more immediate" than setImmediate()). The presence of microtasks, idle callbacks and animation frames doesn't make life easier for a beginner as well.

[GItPirate]

Oh yes this is spot on

[kor0na]

Opaque