I am having an issue where when I change a component in my app, many unrelated components seem to be rerendering too. When I use the Vue performance timings config, I see something like (all in the span of about 200ms)
I am trying to figure out what causes these components to rerender. I saw a tip about how to tell the cause of a rerender, but when I put this snippet* in all the rerendering components, I don’t get anything logged to the console.
So, how can I find what is causing all these components to rerender?
*The code I actually put looks like
public mounted() {
let oldData = JSON.parse(JSON.stringify(this.$data));
this.$watch(() => this.$data, (newData) => {
console.log(diff(oldData, newData));
oldData = JSON.parse(JSON.stringify(newData));
}, {
deep: true,
});
}
Using the F12 dev tools in Chrome, you can track down what is triggering your component to re-render. Add an updated hook to your component as below:
updated() {
if (!this.updateCnt)
this.updateCnt = 1;
if (this.updateCnt > 1) { // set to desired
debugger;
}
console.log(`Updated ${this.updateCnt++} times`);
}
}
Refresh your page in Chrome with F12 tools open and wait for breakpoint to be hit. In the Sources tab, you will see the call stack on the right, with your updated() function as the current stack frame. Look back up the call stack and eventually you should see the code that caused the update to trigger. In my case, it was reactiveSetter() in the vue runtime, which was triggered by me setting a property in a parent component.
The code you have above will only trigger if a component's own state changes, not a parent.
Related
I have made some sandbox code of my problem here:
https://codesandbox.io/s/clever-zeh-kdff1z
<template>
<div v-if="started">
<HelloWorld :msg="msg" #exit="exit" #remake="remake" />
</div>
<button v-if="!started" #click="started = !started">start</button>
</template>
<script>
import HelloWorldVue from "./components/HelloWorld.vue";
export default {
name: "App",
components: {
HelloWorld: HelloWorldVue,
},
data() {
return {
started: false,
msg: "Hello Vue 3 in CodeSandbox!",
};
},
methods: {
exit() {
this.started = false;
},
remake() {
this.msg = this.msg + 1;
//this code should recreate our child but...
this.exit();
this.started = true;
// setTimeout(() => {
// this.started = true;
// });
},
},
};
</script>
So! We have 2 components parent and child. The idea is simple - we have a flag variable in our parent. We have a v-if statement for this - hide / show an element depend on the flag value "false" or "true". After we toggle the flag - the child component should be recreated. This is the idea. Simple.
In our parent we have a button which will set the flag variable to "true" and our child will be created and will appear on our page.
Ok. Now we have 2 buttons inside our child.
One button is "exit" which is emit an event so the flag variable of parent will set to "false" and the elemint will disappear from our page(It will be destroyed btw). Works as charm. Ok.
The second button "remake". It emit event so the flag variable will be just toggled (off then on). Simple. We set to "false", we set to "true". So the current child should dissapear, and then imediatly will be created new one.
But here we are facing the problem! Ok, current child is still here, there is no any recreation, it just updates current one... So in child I have checked our lifecycle hooks - created and unmounted via console.log function. And the second button dont trigger them. Start->Exit->Start != Start->Remake.
So can anyone please explain me why this is happening? I cant figure it out.
Interesting thing, if you can see there is some asynchronous code commented in my demo. If we set our flag to "true" inside the async function the child will be recreated and we will see the created hook message but it seems like crutch. We also can add a :key to our component and update it to force rerender, but it also seems like a crutch.
Any explanations on this topic how things work would be nice.
Vue re-uses elements and components whenever it can. It will also only rerender once per tick. The length of a 'tick' is not something you should worry yourself about too much, other than that it exists. In your case the this.exit() and this.started = true statements are executed within the same tick. The data stored in this.started is both true in the last tick and the current tick as it does not end the tick in between the statements, and so nothing happens to your component.
In general you should think in states in Vue rather than in lifecycles. Or in other words: What are the different situations this component must be able to handle and how do you switch between those states. Rather than determining what to do in which point in time. Using :key="keyName" is indeed generally a crutch, as is using import { nextTick } from 'vue'; and using that to get some cadence of states to happen, as is using a setTimeout to get some code to execute after the current tick. The nasty part of setTimeout is also that it can execute code on a component that is already destroyed. It can sometimes help with animations though.
In my experience when people try to use lifecycle hooks they would rather have something happen when one of the props change. For example when a prop id on the child component changes you want to load data from the api to populate some fields. To get this to work use an immediate watcher instead:
watch: {
id: {
handler(newId, oldId) {
this.populateFromApi(newId);
},
immediate: true
}
}
Now it will call the watcher on component creation, and call it afterwards when you pass a different id. It will also help you gracefully handle cases where the component is created with a undefined or null value in one of the props you expect. Instead of throwing an error you just render nothing until the prop is valid.
First, let me say that the v-navigation-drawer works as intended, i.e.:
On clicking the hamburger menu the TOGGLE_DRAWER mutation is committed, and it toggles open/closed, updating the state.
On window resize it opens/closes at a designated breakpoint
So it works.
BUT the window resize does not properly toggle the mutation and I keep getting a Vuex mutation error when I resize the window:
I understand why I'm getting this error - the $store.state.ui.drawer is being modified outside of the mutator (it's the v-navigation-drawer's v-model):
<v-navigation-drawer
v-model="$store.state.ui.drawer"
app
clipped
>
I get it's bad form to bind the state to the v-model. But when I try to make a drawer computed property with a get() and set() method that properly gets/commits a mutation, the browser crashes (presumably because the set method triggers an endless loop of commits toggling drawer true/false into infinity):
computed: {
drawer: {
get () {
return this.$store.state.ui.drawer
},
set () {
this.$store.commit('TOGGLE_DRAWER') // <--crashes the browser
}
}
}
I've searched endlessly for a solution to this problem. It's bugging me even though it visually appears to be working.
I've considered running the v-navigation-drawer in stateless mode and handling all the window resize events and state updates manually. I've also considered disabling 'Strict' mode in Vuex (which would hide the errors). But the former is a lot more complexity and the latter is a bandaid that costs me debugging insight in development.
This sounds like a perfect candidate for Lodash's debounce function. If you need to stick with using setter/getter while applying this effect, have a look at this post; otherwise, this one for sequential event subscription on any of the lifecycle hooks.
After spending some time with this, I think I have a solution. Wanted to share for anyone else that may be facing the same issue with VNavigationDrawer using Vuex state to control visibility.
The #input event passes a val parameter, which includes the state of the drawer after the window resizes. I created a new action that is called by the below function:
<v-navigation-drawer
:value="$store.state.ui.drawer"
app
clipped
#input="updateDrawer($event)"
>
Here is the action being dispatched:
methods: {
updateDrawer(event) {
if (event !== this.drawer) { // avoids dispatching duplicate actions; checks for unique window resize event
this.$store.dispatch('updateDrawer',event)
}
}
},
And the action commits the new val to the Vuex store.
Basically, the input event is able to watch for updates to the drawer, and subsequently update the drawer state if it's necessary.
You'll also see above that I stubbornly accepted using :value as the docs suggest, even though I think this should be controlled by a v-model.
Seems to be working - with the right events called and the state being updated appropriately.
I have a call in my created method which has an await.
I want to know that the results of that call are loaded so that i can conditionally show/hide things in the DOM.
Right now it looks like the DOM is being rendered before that method has completed. But I though that methods in created were called before the DOM rendered?
You're correct in assuming that the created hook runs before the component mounts. However, the lifecycle hooks are not waiting for async calls to complete. If you want to wait for that call to be completed and data to load, you can do so by using a Boolean that you set to true when your data has loaded.
Your template:
<div v-if='dataLoaded'>Now you can see me.</div>
in your vue instace
export default {
data () {
return {
dataLoaded: false
}
},
created () {
loadMyData().then(data => {
// do awesome things with data
this.dataLoaded = true
})
}
}
This way you can keep your content hidden until that call has resolved. Take care with the context when you handle the ajax response. You will want to keep this as a reference to the original vue instance, so that you can set your data correctly. Arrow functions work well for that.
I am creating a tab component that loads its v-tab-item components dynamically, given an array of configuration objects that consist of tabName, id, and tabContent which is a resource location for the component. I have it successfully loading the components. However, they don't actually initialize (or run their created() methods) until I switch tabs. I just get empty tabs with the correct labels. Using the DOM inspector initially shows just <componentId></componentId>, and then when I switch tabs, those tags are replaced with all of the component's content.
How do I get the dynamic components to initialize as soon as they are loaded?
EDIT: I created a CodePen here:
https://codepen.io/sgarfio/project/editor/DKgQON
But as this is my first CodePen, I haven't yet figured out how to reference other files in the project (i.e. what to set tabContent to so that require.js can load them up). I'm seeing "Access is denied" in the console, which makes it sound like it found the files but isn't allowed to access them, which is weird because all the files belong to the same project. So my CodePen doesn't even work as well as my actual project. But maybe it will help someone understand what I'm trying to do.
Also, after poking around a bit more, I found this:
http://michaelnthiessen.com/force-re-render/
that says I should change the key on the component and that will force the component to re-render. I also found this:
https://v2.vuejs.org/v2/guide/components-dynamic-async.html
Which has a pretty good example of what I'm trying to do, but it doesn't force the async component to initialize in the first place. That's what I need the async components to do - they don't initialize until I switch tabs. In fact they don't even show up in the network calls. Vue is simply generating a placeholder for them.
I got it working! What I ended up doing was to emit an event from the code that loads the async components to indicate that that component was loaded. The listener for that event keeps a count of how many components have been loaded (it already knows how many there should be), and as soon as it receives the right number of these events, it changes the value of this.active (v-model value for the v-tabs component, which indicates which tab is currently active) to "0". I tried this because as I noted before, the async components were loading/rendering whenever I switched tabs. I also have prev/next buttons to set this.active, and today I noticed that if I used the "next" button instead of clicking on a tab, it would load the async components but not advance the tab. I had already figured out how to emit an event from the loading code, so all I had to do at that point was capture the number of loaded components and then manipulate this.active.
I might try to update my CodePen to reflect this, and if I do I'll come back and comment accordingly. For now, here's a sample of what I ended up with. I'm still adding things to make it more robust (e.g. in case the configuration object contains a non-existent component URL), but this is the basic gist of it.
created: function() {
this.$on("componentLoaded", () => {
this.numTabsInitialized++;
if(this.numTabsInitialized == this.numTabs) {
// All tabs loaded; update active to force them to load
this.active = "0";
}
})
},
methods: {
loadComponent: function(config) {
var id = config.id;
var compPath = config.tabContent;
var self = this;
require([compPath], function(comp) {
Vue.component(id, comp);
self.$emit("componentLoaded");
});
}
}
I have a component with a created method:
created() {
this.initMap();
}
The initMap is to initialize Google maps, depending on whether the URL segment corresponds to 'map' or not like so:
initMap() {
const pathname = location.pathname.replace(/\/+$/, '');
const segment = pathname.split('/').pop();
if (segment === 'map') this.showMap();
}
The above bit of code has a ShowMap method that performs a Vuex commit:
showMap() {
this.$store.commit('showMap');
}
This commit however never shows up in my Vue.js devtools(under Vuex).The components watching the Vuex store value that showMap is changing also never trigger.
If I do this however:
setTimeout(() => {
this.$store.commit('showMap');
, 100);
Everything works exactly as expected.
I tried this because the changes actually happen in my Vue.js devtools, because if I look under state I can see updated values.
The Vuex commit seems to fire too fast. Is there anything that can be done about this? Why is this happening in the first place?
I can even put a console.log() into the showMap commit and it works but it still does not get picked up in the devtools and without the setTimeout all of my watcher still don't properly trigger.
Since this was a while ago I am not 100% sure how I fixed this but I think it was by using $nextTick from Vue.js.
By waiting on nextTick you ensure that your call stack for DOM updates has been cleared. This prevents DOM updates that might rely on other parts of your DOM from firing too fast.
Obviously this is way more reliable than simply setting a setTimeout with a given number of let's say 100 milliseconds from my example because if your DOM does not update in time it might still pass this window.
If setTimeout fixed your issue I suggest trying $nextTick.
https://v2.vuejs.org/v2/api/#Vue-nextTick