I have webpack setup to bundle all of the source. I have a Vue object that is the page and multiple Vue components of my own creation. This works great!
I am now getting reference data from the database to fill in certain default options for some of these components. In my pages Mounted or Created events (there is no difference for my question) I am calling a method that will check to see if the data exists in localStorage and if not, it will extract the data from the database.
Once Extracted, I have it in localStorage so it is not an issue. However, the first time I need to gather the data (or when I need to refresh it because I have another trigger that lets me know when it has changed) the page and components have rendered (with errors because of lack of data) before the data comes back. The fetch method is in a promise, but mounted events don't seem to care if a promise exists within in before it continues to the next component.
So what is the best practice for loading/refreshing reference data in Vue? I am currently not using VueX because this is not a SPA. Sure, it is a single page that is doing things (there are many single pages that do their own thing in this site) but I have no need to make it a full SPA here. But If VueX and its store will give me some sort of guarantee that it will occur first or page/components will run AFTER VueX things, I will learn it.
Have you tried doing so:
<component v-if="page.isDataLoaded">...</component>
in your Vue-component:
data() {
return {
page: {
isDataLoaded: false,
}
}
},
mounted() {
this.fetchPageData().then(() => this.page.isDataLoaded = true);
}
You can use v-if and v-else to show, for example page loader element like so:
<PageLoader v-if="!page.isDataLoaded"></PageLoader>
<component v-else>...</component>
Related
Consider the following Widget component.
<template>
<component :is="name" />
</template>
<script>
import { mapActions } from 'vuex';
export default {
props: {
name: {
type: String,
required: true
}
},
created() {
this.addWidget(this.name);
},
methods: {
...mapActions({
addWidget: 'widgets/add'
}) // adds widget name to an array
}
};
</script>
I want to have multiple components like this one all over the page.
I need to be able to gather all of the component names so I can fetch the relevant data for them.
My current idea is to add the component name to the store when the created hook fires.
That works just fine, but my problem is that I can't find a way to dispatch a Vuex action to fetch the data once all of the components have been created. I tried using various hooks to no avail since none of them seems to have Vuex access.
Am I missing something? Is there some kind of hook that fires after all of the components have been created (SSR) that has Vuex access. Or maybe there's some better way to achieve what I've been trying to do?
Why do you want to wait until all the widgets have been loaded to fetch the data? Instead, what I'd do is fetch the data for each Component as they get added in the page. Using this approach, each component would require a specific piece of data, and nothing better than to load each of them in a different request. Easier to test, easier to trace, adheres to the single responsibility principle.
If you are worried that two components may require the same data, then you can route all requests through an Object that hashes the request (endpoint + verb if using REST) and keeps a pool of active connections, so that if two requests come in one reuses the Promise of the other, and only one of them reaches the server.
Now, if you really want to do it using your original approach, make it so that each widget emits an event once it's been registered. The events are collected by the parent component (maybe the Page that loads all the widgets). The page knows which Widgets are being loaded. Every time an event is received it sets a flag on that specific widget to indicate it's been loaded. Once all widgets get a flag, the Page triggers a request to fetch the data.
I have a vue spa app. I fetch data for the page in the created hook
My question is how can i avoid fetching data again for the page that has been previously navigated away from if back button is pressed
EDIT
my app is in vue 3 I later used < keep-alive > which worked but am unable to clear the cache even when using max prop on the < keep-alive :max="2" > component
Quite simply, by caching it.
There are several ways to implement some kind of caching, but it largely depends on your current setup.
If you are not using vue-router and the back button causes your page to re-render, you will need to persist the data some other way, such as by using localStore. If you're using vuex, and you want to persis the data, you can try vuex-persistedstate. I'm assuming though that you are not looking to persist the data and the page is not re-loading on redirect.
If you are already using vuex, you can cache the data in the store.
Another option is to use the keep-alive component
If you don't want to rely on a 3rd party tool, you can also wrap your API call with a caching function.
Here is what that may look like. When the data is loaded, it gets cached, and when the cache exists, the cached result is returned as a promise, so that the method returns the same type either way.
let getMyDataCache = null;
export const getMyData(){
if (getMyDataCache) return new Promise((resolve)=>resolve(getMyDataCache));
return fetch('http://example.com/movies.json')
.then(response => response.json())
.then(data => {
getMyDataCache = data;
return getMyDataCache;
});
}
You could use vuex to store the state for your page - then in your created() hook, check if the state has been populated before fetching the data.
To clarify (since this answer is getting downvoted and I'm not sure why): you need to store the fact that you have already fetched your data somewhere. You can't do it inside your component since it will be remounted when you return to the page. If you have a state management pattern in place (e.g. with Vuex), you can store your data there so that when the component is remounted, you can check your store to see if the data has already been fetched before you try to fetch it again.
If you are using vue-router, the answers on this thread might help you instead: How to make certain component "keep-alive" with router-view in Vue 3?
I am getting some strange behavior in my Vue application that I am developing.
In my view I define my data initially:
...
data() {
return {
organization: {
selectedOption: null,
options: [],
},
};
},
...
Intention is to populate this via a call to my backend API, which I do using => notation via axios:
// The following snippet is in my methods:
...
axios.get('http://localhost:8000/api/org/types')
.then((response) => {
Object.keys(response.data).forEach((k) => {
this.organization.options.push({
value: k,
text: response.data[k],
});
});
this.organization.selectedOption = this.organization.options[0].value;
});
...
The data comes in, and I can see it indeed does set the values until I go elsewhere within the view.
I initially called the method above in the beforeMount() method however I moved it to the created() method (due to data context/reactivity matters) and all seemed to be working just fine.
Now I am having an issue where when accessing the data where it is always seemingly set to initial data I have defined. I am verifying this via debug/console.
Within mounted():
console.log(this.organization); // Returns observer that shows the data I would expect to be there via Console, but initial data when accessing anything.
console.log(this.organization.selectedOption); // Returns null
Is there something I am not understanding how the Vue data method works? I was under the assumption that after the context has been created the underlying data can then be mutated for the life-cycle of that view.
EDIT:
I did attempt to return the promise on the axios call, but to no avail.
There are a couple of keys things to note here.
Firstly, when you log an object to the console it is live. You'll probably see a little blue 'i' icon after you expand the object that explains this. What this means is that the object properties are not copied. Instead the console just has a reference to the object. It only grabs the property values when you click on the object in the console to expand it. You can work around this by logging out console.log(JSON.stringify(this.organization)) instead.
The second point to note is that it really doesn't matter which hook you use to load the data. The hooks beforeCreate, created, beforeMount and mounted will all run synchronously at the relevant stages. Meanwhile, your data is being loaded asynchronously. Vue won't wait for it, there's no support for that. No matter which hook you use the data won't be loaded until after the initial rendering/mounting is complete. This is a common problem and you just need to write your component in such a way that it can cope with the data being missing when it first renders.
To be clear, I'm not saying that the hooks are interchangeable in general. They most definitely aren't. It's just that when you're loading data using an AJAX request it doesn't make any real difference which you use. The AJAX request will always come back after all of those hooks have been run. So performing the request in an earlier hook won't make the data available in the later hooks.
A common alternative is to load data in a parent component and only create the child once the data is loaded. That's usually implemented using a v-if and the data is then passed using a prop. In that scenario the child doesn't have to deal with the data being missing.
Sorry if this is a repeat - I have had a look around and spent most of today on this issue without getting result I am after.
https://github.com/vahidhedayati/micronaut-vuejs-cqrs/blob/master/frontend/src/components/sample/dynamicForm/PropertySplit.vue#L29
https://github.com/vahidhedayati/micronaut-vuejs-cqrs/blob/master/frontend/src/components/sample/dynamicForm2/Property2.vue#L31
I have two similar vue parent pages that load up dynamic form content, what I am trying to do is to get the actual form content which resides on a totally different .vue file in each of the sub folders above.
If I use Vue.component('form-content' this does work but I end up with 1 instance of the form for both different calls rather than a dynamic form per call. So one of the two forms gets loaded in and reused on both calls.
I have tried to use a const variable instead of Vue.component which works correctly locally on the main vue page that loads in the const variable but I haven't been able to get child page to load up the const value
//import Vue from 'vue'
//Vue.component('form-content', {
// components: { ActualForm },
// template: `<actual-form></actual-form>`
//});
//const content = {
// components: { ActualForm },
// template: `<actual-form></actual-form>`
//}
ActualForm.vue is another page and ideally I want to be able to pass this dyanmically per call on different page to the underlying DynamicForm.vue which will load title etc and then the form as per vue page that is passed in.
It seems trivial not quite sure why I am struggling with this.
You cannot pass a component to another component through a prop. For that you need to use a slot. So your code would look like:
<dynamic-form
:headingText="currentHeadingText"
:sectionHeadingText="currentSectionHeadingText"
>
<actual-form/>
</dynamic-form>
And in the <dynamic-form> component you would write:
<template>
[…]
<slot></slot>
[…]
</template
Then the <actual-form> component would be included at the position of the <slot>-tag. You can also use multiple slots and pass in multiple components / template segments. (Read the docs on vuejs.org for detailed information)
I am not completely sure what you are trying to do though. Maybe you need to structure your application in a different way. E.g. use the <dynamic-form> in the template of the <actual-form>. You could then still pass props to <dynamic-form> and fill slots therein from the <actual-form>.
I'm trying to show an activity indicator, when I go from one page to another. The target page contains many components within it, and it takes time to load. that's why I need some way to listen when all the child components are loaded, and at that moment tell my variable isBussy to be false
<template>
<StackLayout>
<ActivityIndicator :busy="isBussy" v-if="isBussy" />
<StackLayout v-else>
<Component1 />
<Component2 />
<Component3 />
<Component4 />
</StackLayout>
<StackLayout>
</template>
<script>
import Component1 from '~/components/Component1'
import Component2 from '~/components/Component2'
import Component3 from '~/components/Component3'
import Component4 from '~/components/Component4'
export default {
data() {
return {
isBussy: true
}
},
mounted() {
this.$nextTick(function() {
// Code that will run only after the
// entire view has been re-rendered
this.isBussy = false
})
}
}
</script>
this code does not work, since once the navigation is indicated from the previous page with:
#tap="$goto('otherPage', { props: { foo: bar } })"
it remains stuck on the initial page, and all the components begin to load in the background of the destination page, but without displaying the parent page, changing to this, only when the whole process ends, and never show/hide the activity indicator as expected.
By the way this expected behavior works perfectly when i do request and process them with Promises, then I turn on or off a variable in the state and it works. but I can not replicate that behavior in the navigation between pages and listen to load all the components
EDIT
Finally I achieved the desired behavior with a little trick I found on the internet
mounted() {
setTimeout(() => {
this.isBussy = false
}, 500)
},
this causes that the rendering of all the children components is delayed only a little, so that the activity indicator is shown, but not too much to produce that none of the components contained in the else block is detected and begin to rendering
There are two main ideas to understand here I think. I'll describe both.
1. General technique to Fetch Data without blocking render
It sounds like you understand this concept at the parent component level but then are asking how to do something very similar for the child components that this page contains.
The way I handle this, is in my component, I have my data default to an isLoading state. Then, in beforeMount() or mounted(), I perform my asynchronous actions and make necessary changes to my page's data.
The problem becomes entirely recursive when we look at child components. You want to make sure your child components are rendering and that any long running data fetching that needs to occur within their implementation will simply cause them to re-render once that fetching is complete.
Here is a working example: https://codesandbox.io/embed/r4o56o3olp
This example uses Nuxt. Aside from the addition fetch() and asyncData() methods, the rest of the Vue lifecycle hooks are the same here.
I use new Promise and setTimeout to demonstrate an operation that would use promises and be asynchronous. (e.g. axios.get(..))
The About page loads, and the beforeMount() lifecycle hook performs the asynchronous fetching in a way that doesn't block the page from rendering.
I use the beforeMount() hook because, according to here ( https://alligator.io/vuejs/component-lifecycle/ ), it is the first lifecycle hook that we have access to once the page's data is reactive. (So modifying this.myDataProp would trigger a re-render if {{ myDataProp }} was used in the template).
I also included a child component where I purposely made its data take twice as long to load. Since I again, am letting the component render immediately, and then I handle the fetching/updating of data in an appropriate lifecycle hook, I can manage when the end-user perceives a page to be loaded.
In my working example, the LongLoadingComponent did the same exact technique as the About page.
Once you see how to use beforeMount() or mounted() to fetch data and then update state, I think the trick is to take a moment and really think about the default state of your component. When it first renders, what should the user see before any of it's data fetching/long-running operations are completed?
Once you determine what your default (not yet loaded) component should look like, try getting that to render on your screen, and secondarily add in the logic that fetches and updates state data.
2. Listening for when a Child Component is finished rendering from a parent component
This makes use of the above technique, but includes the usage of the updated() hook and emitting a custom event ( https://v2.vuejs.org/v2/guide/components-custom-events.html
)
If you really want to listen for when your child components are finished rendering, you can $emit a custom event in your updated() hook. Perhaps something like this (in one of your child components)
if (this.dataLoaded) { this.$emit('loadedAndRendered') }
So when the child's async operations are done, it can flip it's dataLoaded property to true. If dataLoaded is used in the child's <template> somewhere, then the component should re-render (for it's "finished" state). When the child re-renders, the updated() hook should trigger. (again, see: https://alligator.io/vuejs/component-lifecycle/ ) I included the if (this.dataLoaded) part just to handle case where updated() hook might be called during intermediate data updates. (We only want to emit loadedAndRendered event if child is finished loading data/updating.)
3. Other caveats about universal nuxt applications
It wasn't until after I wrote this answer that I realized you aren't using Nuxt. However I'm adding this in case other Nuxt users happen to come across this.
I'm adding this section just because it took some focused hands-on time for me to wrap my head around. A Nuxt Universal Application does both server-side and client-side rendering. Understanding when something renders on the client vs when it was rendered on the server was a little difficult for me at first. In the working example I linked above, when you visit the about page you can also see if that component was fetched from the server or if it was just rendered by the client.
I'd recommend playing with a Page's fetch() and asyncData() methods and see how it impacts when certain things render on your screen. ( https://nuxtjs.org/api/pages-fetch/ ) ( https://nuxtjs.org/api/ ). Seeing what these methods are useful for helps me also identify what they are not useful for.
If you're using a Vuex store, I'd recommend seeing what happens when you refresh a page or use instead of a to navigate between pages. (Seeing something like the SSR schema diagram can be helpful here: https://nuxtjs.org/guide#schema )
..I have yet to fully appreciate the details of the bundling and delivery behavior that Webpack provides for a Universal Nuxt app (See right side of diagram here: https://medium.freecodecamp.org/universal-application-code-structure-in-nuxt-js-4cd014cc0baa )