We Keep Coding

Why is the reactive Value sometimes not updating in template? (Vue)

I have a simple h3 tag containing a title that is bound to a reactive data property.
I am fetching the value from a Firestore database and assign it to the data property. When I don't reload and access the page through client-side navigation, everything works fine.
However once I reload the title value gets updated properly (seen in console logs and vue dev tools) but the h3-tag remains empty.
Here is the code:
<template>
<h3 #click="displayCoursePreview" class="mt-5">{{ titl }}</h3>
</template>
<script>
props: {
student: {
type: Boolean
}
},
watch: {
rehydrated: {
// Always triggers once store data is rehydrated (seems to work without any problems)
immediate: true,
async handler(newVal, oldVal) {
if (newVal) {
await this.getSections();
return this.getTopics();
}
}
}
},
data() {
return {
titl: null
};
},
computed: {
rehydrated() {
return this.$store.state.rehydrated; // Equals true once store is rehydrated from local storage
}
},
methods: {
getSections() {
console.log('running') // Runs every time
let ref = this.$store.state.courses;
var cid = this.student
? ref.currentlyStudying.cid
: ref.currentlyPreviewing.cid;
// Get Course Title
this.$fireStore
.collection("courses")
.doc(cid)
.get()
.then(doc => {
console.log(doc.data().name) // Logs correct title every time
this.titl = doc.data().name;
this.thumbSrc = doc.data().imgsrc;
})
.catch(err => console.log(err));
}
</script>
I can't figure out why it sometimes displays the title and sometimes does not. Is there another way to bind titl to the content of the h3-tag without the {{}} syntax?
Thank you in advance!
EDIT:
I have changed the {{}} syntax to v-text like so:
<h3 #click="displayCoursePreview" class="mt-5" v-text="titl"></h3>
And now it works every time, even after a hard reload. Can anyone explain the difference and why this works?

To answer the original question it looks like you might have a race condition between this component and the store. The watch will only trigger 'getSections' if it sees a change in this.$store.state.rehydrated after it's been mounted, but the store might have completed that before this component got mounted, so then the watch never gets triggered.
Not sure why switching to v-text would have altered this, maybe it allows the component to mount slightly faster so it's getting mounted before the store completes it's rehydration?

Is it possible for Vue.js to automatically update the view when a third-party JSON is updated?

I'm trying to accomplish the following but I don't even know if it is even possible with Vue as I'm struggling to get the desired result:
I have an endpoint for an API which returns many objects within an array.
I am successfully rendering the data within my Vue application but I wanted to know if it is possible for Vue to "track" when the array has been updated with more objects and then render those in the view.
I am using setInterval to perform a GET request every 10 minutes and the new data is going into the object within my data() correctly but the changes are not reflected within the view.
At the moment I am changing a boolean from true to false at the beginning and end respectively so that the view is rendered again with v-if.
My goal is to create a simple Twitter feed app that performs a GET request every 10 minutes, collects the tweets, puts them into my Vue instance and show them in the view without having to reload the page/re-render the component. Like an automatic Twitter feed that just constantly loads new tweets every 10 minutes.
Is this even possible? I've tried using the Vue.set() method but that hasn't made any difference.
If it's not possible, what would be the best way to implement something similar?
Here is my code:
JavaScript:
new Vue({
el: '#app',
data: {
items: [],
},
created() {
this.load();
setInterval(() => this.load(), 5000);
},
methods: {
load() {
axios.get('https://reqres.in/api/users?page=2')
.then(response => {
this.items = response.data.data;
});
}
}
});
HTML
<div id="app">
<p v-for="item in items">
{{ item.first_name }}
</p>
</div>
CodePen: https://codepen.io/tomhartley97/pen/VwZpZNG
In the above code, if the array is updated by the GET request, the chances are not reflected within the view?

Yes it is possible. The way you need to set new reactive properties in your Vue instance is the following:
For Object properties: Vue.set(this.baseObject, key, value)
The baseObject cannot be a Vue instance or the base data() object, so you will have to declare a container property.
For Array entries use native array methods: e.g. Array.prototype.push().
Using Vue.set(array, arrayIndex, newArrayElement) does not work
Hence, your solution might look something line that:
<script>
export default {
data() {
return {
response: [],
};
},
mounted() {
setInterval = (() => this.getData), 600000);
}
methods: {
async getData() {
const res = await request();
const resLength = res.data.length;
for (let i = 0; i < resLength; i++) {
// check if entry is already in array
const entryExists = this.response.some((entry) => {
return entry.id === res.data[i].id
})
if (!entryExists) {
// this will make the array entries responsive, but not nested Objects
this.response.push(res.data[i]);
// to create nested responsive Objects you will have to set them explicitly
// e.g. Vue.set(this.response[this.response.indexOf(res.data[i])], nestedObjectKey, res.data[i].nestedObject)
}
}
}
}
};
</script>

Well, I view the codepen, I known why your view do not get update: the api response always return the same array!
Try to return different data.
The api returns an array, so the data defines
data() {
return {
array: [] // array that api returns
}
}
The template may look like this
<div v-for="item in array">
</div>
And the update methods
update() {
setInterval(async () => {
let resp = await api()
this.array = resp.data.concat(this.array)
}, TEN_MINUTES)
}

Reactivity problem with mapGetters only on first load

I am using the mapGetters helper from VueX but i have some problem only on the first load of the page, it's not reactive...
Let me show you :
my html template triggering the change :
<input type="number" value="this.inputValue" #change="this.$store.dispatch('setInputValue', $event.target.value)">
my store receiving the value
{
state: {
appValues: {
inputValue: null
},
},
getters: {
getInputValue: (state) => {
return state.appValues.inputValue;
},
},
mutations: {
setInputValue(state, value) {
state.appValues.inputValue = value;
},
},
actions: {
setInputValue(context, payload) {
return new Promise((resolve, reject) => {
context.commit('setInputValue', payload);
resolve();
});
},
}
}
and then my component listening the store :
import {mapGetters} from 'vuex';
computed: {
...mapGetters({
inputValue: 'getInputValue',
}),
}
watch: {
inputValue: {
deep: true,
immediate: true,
handler(nVal, oVal) {
console.log("inputValue", nVal, oVal);
}
},
}
So now, when i first load the page I get this console.log "inputValue" null undefined which is totally normal because as I have nothing in my store it gaves me the default value null.
But now it's the weird part. I start changing the input value and I don't have nothing appearing in my console. Nothing is moving...
Then I reload the page and on the load I get this console.log "inputValue" 5 undefined (5 is the value I entered previously) so as you can see, when I was changing the input previously, it was well keeping the value in the store but the computed value was not updating itself...
Ans now, when I change the value of the input I have my console log like this "inputValue" 7 5 so it's working as I would like it to work from the start...
What do I do wrong? Why on the first load the computed value not reactive?
Thanks for your answers...

I think the best way to solve this issue is to store a local variable with a watcher, and then update vuex when the local is changed:
On your component:
<input type="number" v-model="value">
data() {
return {
value: ''
};
},
computed: {
...mapGetters({
inputValue: 'getInputValue'
})
}
watch: {
value(value){
this.$store.dispatch('setInputValue', value);
},
inputValue(value) {
console.log('inputValue', value);
}
},
created() {
// set the initial value to be the same as the one in vuex
this.value = this.inputValue;
}

Please take a look at this sample: https://codesandbox.io/s/vuex-store-ne3ol
Your mistake is, you are using this keyword in template. One shouldn't use this in template code.
<input
type="number"
value="inputValue"
#change="$store.dispatch('setInputValue', $event.target.value)"
>
Bonus tip: It is redundant to use a getter to return the default state
if you can just use mapState to return the state.

There are a few small mistakes in the template. It should be this:
<input type="number" :value="inputValue" #change="$store.dispatch('setInputValue', $event.target.value)">
I've removed the this. in a couple of places and put a : out the front of value. Once I make these changes everything works as expected. The this.$store was causing console errors for me using Vue 2.6.10.
I would add that you're using the change event. This is the standard DOM change event and it won't fire until the field blurs. So if you just start typing you won't see anything happen in the console. You'd be better off using input if you want it to update on every keystroke. Alternatively you could use v-model with a getter and setter (see https://vuex.vuejs.org/guide/forms.html#two-way-computed-property).
My suspicion is that when you were reloading the page that was triggering the change event because it blurred the field.

Ok, so ... I found the problem and it was not relative to my examples, I can't really explain why, but I'll try to explain how :
In my store I have the next method :
mutations: {
deleteAppValues(state) {
state.appValues = null;
}
}
I was using this one on the Logout, or when the user first comes on the pageand was not logged-in... So what was going-on?
The User first load the page, the store is initializing well, and the index inputValue is initialized with null value, so it exists...
... But as the User is not logged, I destroy the store so now the inputValue is not equals to null, it just doesn't exist...
Trying to use mapGetters on something that don't exists, the reactivity won't work, so if I dispatch a change, the store key will be created, but as the mapGetters was initialized with an inexisting key, it doesn't listen the reactivity...
After reloading the page, the key now exists in the store so the getter can be attached to it and so now everything working fine...
This is exactly the explaination of what was going wrong about my code... So to make it works fine, I just changed my destruction mutation to :
mutations: {
deleteAppValues(state) {
state.appValues = {
inputValue: null,
};
}
}
Like this, the inputValue key of the store object will always exists and so the getter won't lose his reactivity...
I tryed to make a simple concise question but that made me forgot the bad part of my code, sorry.

VueJs + Laravel - like button component

I'm trying to get a good understanding of VueJS, and I'm using it with Laravel 5.7 for a personal project, but I can't exactly figure out how to do a, probably, simple task a "like" button\icon.
So, here's the situation, I have a page, displaying various posts from my database, and at the bottom of each post I want a "like toogle" button, which I made with an icon followed by the number of likes on that post; At first the button will contain the data retrieved from the corresponding database table, but if you click it will increase the displayed number by one and insert a new like in the database.
I made the "like" icon as a component :
<section class="bottomInfo">
<p>
<likes now="{{ $article->likes }}"></likes>
<span class="spacer"></span>
<span class="entypo-chat">
{{ $article->comments }}
</p>
</section> <!-- end .bottomInfo -->
As you can see there's a <likes> in which I added a prop now, by what I'm understanding till now about components, in this way I can insert the data from my db as a starting value (now contains the db row value), problem is, I don't know where\how to keep that value in my app, in which I'm gonna also use axios for increasing the likes.
Here's the component:
<template>
<span class="entypo-heart"> {{ now }}</span>
</template>
<script>
export default {
props: ['now'],
data() {
return {
like: this.now
}
},
mounted() {
console.log('Component mounted.');
}
}
</script>
What I tried to do (and I don't know if it's correct) is to pass the value of now to the data function inside a property named like, so, if I understood correctly, that variable like is now part of my properties in my main Vue instance, which is this one
const app = new Vue({
el: '#main',
mounted () {
console.log("The value of 'like' property is " + this.like)
},
methods: {
toggleLike: function() {
} //end toggleLike
}
});
The mounted function should print that property value, but instead I get
The value of 'like' property is undefined
Why? Is this how it works? How can I make it so I can get that value and also update it if clicked, to then do a request to my API? (I mean, I'm not asking how to do those single tasks, just where\how to implement it in this situation). Am i getting the component logic right?

Probably a bit more verbosity never hurt:
props: {
now: {
type: Number,
required: true
}
}
Instead of using the data function, use a computed property:
computed: {
likes: {
get: function() {
return this.now
}
}
}
However, here comes the problem.
If you need to change the # of likes after the user clicks like, you have to update this.now. But you can't! It's a property, and properties are pure. Vue will complain about mutating a property
So now you can introduce a data variable to determine if the user has clicked that like button:
data() {
return {
liked: 0
}
}
Now we can update our computed property:
likes: {
get: function() {
return this.now + this.liked
}
}
However, what are we liking? Now we need another property:
props: {
id: {
type: Number,
required: true
},
now: {
type: Number,
required: true
}
}
And we add a method:
methods: {
add: function() {
//axios?
axios.post(`/api/articles/${this.id}/like`)
.then (response => {
// now we can update our `liked` proper
this.liked = 1
}).catch(error => {
// handle errors if you need to
)}
}
}
And, let's make sure clicking our heart fires that event:
<span class="entypo-heart" #click="add"> {{ now }}</span>
Finally our likes component requires an id property from our article:
<likes now="{{ $article->likes }}" id="{{ $article->id }}"></likes>
With all this in place; you're a wizard now, Harry.
Edit
It should be noted that a user will be forever able to like this, over and over again. So you need some checks in the click function to determine if they like it. You also need a new prop or computed property to determine if it was already liked. This isn't the full monty yet.

Parent's data change does not update child component in vuejs

I have the following:
Vue.component('times-updated', {
template: '<span>Times Updated: {{ timesUpdated }}</span>',
data: function() {
return {
timesUpdated: this.$parent.myData.timesUpdated
}
}
});
var vm = new Vue({
el: '#test',
data: function() {
return {
myData: {}
}
}
})
setInterval(function(){
$.ajax({
url: `${window.location.href}/json`, // This just returns an array : array.timesUpdated: 2 etc
}).done(function (data) {
vm.myData = data; // changes this data
});
}, 1000)
and am using the following html:
<div class="test">
<times-updated></times-updated>
</div>
I poll a REST API that returns an array which includes a timesUpdated property:
{
timesUpdated: 5
}
My intention is that every second I use jQuery's $.ajax method to call the API, update the myData data object on vm, which would then update the times-updated component.
The code works on initial page load, the times-updated component can retrieve the value on its parent's myData property, but whilst I have confirms that vm.myData does reflect the new value from the API, the component doesn't update its display to show the new count.
What am i doing wrong?

The data function is only called once during the life cycle of the component; when it is initially created. So essentially your component is just displaying the value as it existed when the component was created.
Additionally, it's generally bad practice to reach out of a component to get a data value. Vue is props down, events up. You should convert your component to use a property.
Vue.component('times-updated', {
props:["times"],
template: '<span>Times Updated: {{ times }}</span>',
})
The fact that you are using a function to define the Vue in this particular case doesn't really matter, it's just not a typical practice. Components require a function because they need an isolated scope.
Here is an example.

That callback is required only in components
// vue instance
new Vue({
data: {
status: true
}
};
// vue components (callback)
Vue.component('custom-component', {
data: function() {
return {
status: false
}
}
});