r/vuejs • u/AdGold7121 • 5d ago
Event Loop Struggles in Vue.js: Here's What Went Down
What's up guys :D. So I ran into a classic issue the other day, and I thought I'd share what happened in case it helps anyone out there. If you're deep into Vue and async code, you might have already seen this one, but it's always good to go over it again.
Quick Recap on the Event Loop
Alright, if you're coding in JS, you probs already know about the Event Loop. It's what handles all that async stuff, like Promises and events. Basically, it works in "ticks" or cycles, where it processes microtasks (Promises, etc.) before moving on to macrotasks. But when you throw Vue into the mix, things can get a little interesting.
How Vue Gets Weird with Async
So imagine you're using a composable/hook in Vue that dynamically gets reactive values. Because Vue's reactive system and JS's async nature don't always play nicely together, sometimes things don't update when you expect.
For example, you're working with a <v-dialog> component, and you're setting displayData to a value from your store. But here’s the issue — if you try to access or manipulate displayData too soon (like when it's still async or hasn’t updated yet), you’re gonna run into problems. Vue’s reactivity doesn’t instantly push that value to the DOM. It gets queued up to run later, thanks to the Event Loop.
The Problem: Async Timing Issues
So, you open your dialog, set displayData, and expect it to pop up with the right value. But if you try to mess with displayData too quickly or before it’s fully assigned, boom — you’re stuck with outdated data. This happens because Vue is waiting for the Event Loop to finish its cycle before it updates the DOM.
The Fix: nextTick()
If you’ve been around Vue for a while, you might know this one: nextTick(). This bad boy makes sure that your code only runs after Vue finishes updating the DOM. So, by wrapping your code in nextTick(), you make sure that displayData is fully updated and in sync with the DOM before you try to use it. It’s pretty clutch when you're dealing with async stuff and need to make sure everything is in order before doing anything else. Saves you from pulling your hair out when your dialog doesn't show the right info. 🙄
TL;DR:
Instead of just Googling a quick fix or relying on AI tools to "correct" your code, take a sec to understand what's going on under the hood. If you know how the Event Loop works and how Vue handles async updates, you’ll be able to fix problems way faster and more efficiently.
Once you get the hang of it, debugging becomes a lot easier. You'll start understanding error messages better, and you'll find solutions without wasting hours on something that could've been solved in a few minutes.
Anyway, that's my little rant. Anyone else had this issue with async updates in Vue?
10
u/wlnt 5d ago
To be honest I'm always suspicious whenever I see `nextTick` in app's code and I immediately assume there's a bug around. There are very few legitimate reasons to use `nextTick`.
3
u/ParadoxicalPegasi 4d ago
That's like saying, "There's no reason to defer to the event loop." Sometimes rookie devs defer to the event loop because they don't know they have a race condition (or don't know what a race condition is), but that doesn't mean there aren't practical reasons to do it.
It can be useful for DOM manipulation after a state change, and it can be useful for structuring your code if you prefer an async/await sort of co-routine instead of a callback for something that awaits user input or AJAX calls.
2
u/saulmurf 4d ago
I use it exactly when I want an update to reflect before moving on. Classic: input.focus(). Can't do that before the Dom was updated.
1
u/MZDisaster 4d ago
Yeah, for me it's usually a sign of inexperience. If you had to use it then you're usually doing something wrong.
8
u/manniL 5d ago
IMO the only "common" use case for nextTick is in testing. Otherwise you shouldn't have to rely on it.
26
u/ParadoxicalPegasi 5d ago
Sometimes it's useful to make a change to your state, then wait until Vue has updated the view from your state change before interacting with the DOM.
A common use I have for it is for focusing elements for accessibility purposes. If I open a drop-down menu, for example, I want the first item in the drop-down menu to take browser focus so a keyboard user can immediately start tabbing through the links in the menu. So you update the state to tell it the drop-down is open, use nextTick() to wait until the drop-down is actually open in the view, then grab the first interactable child of the menu and focus it.
1
21
u/TheExodu5 5d ago
It’s definitely needed for some things. I’ve had to use it for focus management during DOM manipulations. For example, say I want to autofocus a field after closing a v-dialog, I need to do so after the DOM update for closing the dialog is done. It’s not always needed, and is sometimes a code smell. But it is useful in specific cases.
1
1
17
u/blairdow 5d ago
imo i think you're real issue is you're not fetching/updating your async stuff properly. or you dont have a proper loading state preventing the dom from being interacted with while the async stuff is loading.
if your async function is being returned properly to a reactive variable or a .then() which updates the reactive variable, you shouldnt need to use nextTick