Vue js dynamically added property not reactive - javascript

I have a component which displays has a prop called obj. obj has two properties: obj.title and obj.body. Each is bound to a textfield so as to be reactive and editable.
<div id="app">
<controller :obj="{title: 'TITLE'}"></controller>
</div>
<template id="controller">
<input type="text" v-model="obj.title">
<p>{{ obj.title }}</p>
<input type="text" v-model="obj.body">
<p>{{ obj.body }}</p>
</template>
The title property is part of the prop which is bound to the component. But the body property has been added dynamically during the created callback. Here is the js:
Vue.component('controller', {
template: '#controller',
props: ['obj'],
created: function() {
this.obj.body = "BODY";
},
});
new Vue({
el: '#app',
});
The problem is that the body property isn't behaving reactively. Changes to the body textfield are not reflected by {{ obj.body }}.
The vue website has a section about Adding and Deleting Properties, but I couldn't get their suggestions to work.
Here is a jsfiddle demonstrating the problem.
Note: it has been suggested that I declare the body property at the same time as the title property. This would work, but for my use-case the property needs to be added dynamically.

Try to declare the body property when passing the prop:
<controller :obj="{title: 'TITLE', body: null}"></controller>
Or in your created method:
created: function() {
this.obj = {
title: this.obj.title,
body: 'some body
}
},
https://jsfiddle.net/crabbly/33721g9w/

I have selected this as the Accepted solution because it is what I would recommend to someone else with the same problem.
As user crabbly noticed, the reactivity can only be re-established if the prop's reference is updated.
I think the nicest way to do this is by making a shallow copy:
created: function() {
this.obj.body = 'BODY'
/**
* ... other code that adds other properties and messes around with obj...
*/
this.obj = Object.assign({}, this.obj);
}
... here, Object.assign is responsible for updating the reference.
This solution is currently not supported by IE, though any "clone" function will do (e.g. this.obj = jQuery.extend({}, this.obj); also works).

Related

How to make a sample that shows the 'Props are overwritten when re-rendering' anti pattern

I would like to be convinced that 'Props are overwritten when re-rendering' is an anti pattern.
const MyButton = Vue.extend({
props: {
obj: {}
},
template:
"<button #click=\"obj.text = 'Value'+Math.round(Math.random()*100)\">Change text in child ({{obj.text}})</button>"
});
const app = new Vue({
el: "#main",
data: {
obj: { text: "Value2" }
},
components: {
MyButton
},
template: `
<div>
<Button #click='obj.text = "Value"+Math.round(Math.random()*100)'>Change text in parent ({{obj.text}})</Button><br>
<MyButton :obj='obj'/> 👈 Pressing here 'mutate' the prop. It is an anti-pattern (Props are overwritten when re-rendering). But it seems to work just fine, how to change this sample so it shows the anti-pattern problem? (https://eslint.vuejs.org/rules/no-mutating-props.html)
</div>`
});
UPDATED Codepen:
https://codepen.io/SVSMITH/pen/LYrXRzW
Can anyone help?
In your example you are actually not mutating the prop, because what you send in to the child is a reference to an object. This reference stays the same. See what happens if you change the template code in your child to:
"<button #click=\"obj = {}\">Change text in child ({{obj.text}})</button>"
Then you will see that the prop is overwritten and the value of the child differs from that in the parent. When the parent updates the value, the updated value in the child will be overwritten. Which can cause serious and hard to find bugs. Therefore use emit in the child to update the value in the parent, which will update the child value through the prop.
If you have a lot of these props and emits, you should look into using a store like Pinia.

Binding Input in Vue not working

I would like to call a function with a value when a user starts typing in an input box. I have tried two approaches.
The first approach is trying to use two-way binding to a model. However, after following the documentation I get an error.
Here is the example from the official docs:
<div id="app-6">
<p>{{ message }}</p>
<input v-model="message">
</div>
var app6 = new Vue({
el: '#app-6',
data: {
message: 'Hello Vue!'
}
})
And here's my example:
<template lang="html">
<input
type="text"
v-model="handle"
/>
</template>
<script>
export default {
data: {
handle: 'model',
}
};
</script>
I am writing this as part of an application so I chose not to recreate the Vue instance and I declared that elsewhere. However, I get this error:
Property or method "handle" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option.
A second approach I've tried is this calling a function directly from the view via an event handler. I'm coming from React so this is my preferable approach. However, the function has undefined as an input value meaning it's not picking up the value of the input.
<template lang="html">
<input
type="text"
v-on:keyup="handleInput()"
/>
</template>
<script>
export default {
methods: {
handleInput(input) {
// input -> undefined
},
},
};
</script>
I really can't see why neither of these works. Wouldn't the expected behavior of an input listener would be to pass the value?
Where am I going wrong?
It seems like you might have to do something like this: How to fire an event when v-model changes ? (vue js). What I don't understand is why you have to manually attach a watcher when you have assigned a v-model? Isn't that what a v-model is supposed to do?
What finally worked was this:
<template lang="html">
<input
type="text"
v-model="searchTerm"
#keyup.enter="handleInput"
/>
</template>
<script>
export default {
data() {
return { searchTerm: '' }
},
methods: {
handleInput(event) {/* handle input */},
},
};
</script>
Shouldn't data be a function on your first example? I think this is how it works for vue components.
<script>
export default {
data: function () {
return { handle: 'model' }
}
};
</script>
I think this was explained somewhere on vuecasts.com, but I might be wrong. :)

Dynamically created input. Can't use $refs so how to get e.g. focus?

I have dynamically created inputs (list with elements, every element has own ID) for an edition.
All of them have v-if to be there only when the edit of the particular element is has been triggered.
Because of that, I can't use $refs as Vue does not see that in refs.
How can I solve it?
I really don't want to add jQuery for that or having to use vanilla JS every time when I need something like that which is quite often.
Usually, we have e.g. a span before editing, and would use v-show rather than v-if on it since we still need it after editing, and each input is coupled with its according span, so something like event.target.nextSibling.focus() will do the job.
I prefer event.target... to $refs as declaring $refs adds complexity to the component's structure while the other is just something only relevant within the click event.
If you really wanted to avoid the use of vanilla js (apart from for focusing) then I'd suggest you have to move your list elements into a component:
Vue.component('list-items', {
template:
`<div>
<button #click="edit">edit</button>
<input v-if="editing" ref="input" type="text" :value="value" #input="$emit('input', $event.target.value)">
</div>`,
props: ['value'],
data () {
return {
editing: false,
}
},
methods: {
edit () {
this.editing = !this.editing
if (this.editing) {
this.$nextTick(() => {
this.$refs.input.focus()
})
}
},
},
})
new Vue({
el: '#app',
data: {
list: [{
title: 'foo',
}, {
title: 'bar',
}]
},
})
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<div id="app">
<list-items v-model="item.title" v-for="item in list"></list-items>
<pre>{{ list }}</pre>
</div>

Vue 2 - Mutating props vue-warn

I started https://laracasts.com/series/learning-vue-step-by-step series. I stopped on the lesson Vue, Laravel, and AJAX with this error:
vue.js:2574 [Vue warn]: Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value. Prop being mutated: "list" (found in component )
I have this code in main.js
Vue.component('task', {
template: '#task-template',
props: ['list'],
created() {
this.list = JSON.parse(this.list);
}
});
new Vue({
el: '.container'
})
I know that the problem is in created() when I overwrite the list prop, but I am a newbie in Vue, so I totally don't know how to fix it. Does anyone know how (and please explain why) to fix it?
This has to do with the fact that mutating a prop locally is considered an anti-pattern in Vue 2
What you should do now, in case you want to mutate a prop locally, is to declare a field in your data that uses the props value as its initial value and then mutate the copy:
Vue.component('task', {
template: '#task-template',
props: ['list'],
data: function () {
return {
mutableList: JSON.parse(this.list);
}
}
});
You can read more about this on Vue.js official guide
Note 1: Please note that you should not use the same name for your prop and data, i.e.:
data: function () { return { list: JSON.parse(this.list) } } // WRONG!!
Note 2: Since I feel there is some confusion regarding props and reactivity, I suggest you to have a look on this thread
The Vue pattern is props down and events up. It sounds simple, but is easy to forget when writing a custom component.
As of Vue 2.2.0 you can use v-model (with computed properties). I have found this combination creates a simple, clean, and consistent interface between components:
Any props passed to your component remains reactive (i.e., it's not cloned nor does it require a watch function to update a local copy when changes are detected).
Changes are automatically emitted to the parent.
Can be used with multiple levels of components.
A computed property permits the setter and getter to be separately defined. This allows the Task component to be rewritten as follows:
Vue.component('Task', {
template: '#task-template',
props: ['list'],
model: {
prop: 'list',
event: 'listchange'
},
computed: {
listLocal: {
get: function() {
return this.list
},
set: function(value) {
this.$emit('listchange', value)
}
}
}
})
The model property defines which prop is associated with v-model, and which event will be emitted on changes. You can then call this component from the parent as follows:
<Task v-model="parentList"></Task>
The listLocal computed property provides a simple getter and setter interface within the component (think of it like being a private variable). Within #task-template you can render listLocal and it will remain reactive (i.e., if parentList changes it will update the Task component). You can also mutate listLocal by calling the setter (e.g., this.listLocal = newList) and it will emit the change to the parent.
What's great about this pattern is that you can pass listLocal to a child component of Task (using v-model), and changes from the child component will propagate to the top level component.
For example, say we have a separate EditTask component for doing some type of modification to the task data. By using the same v-model and computed properties pattern we can pass listLocal to the component (using v-model):
<script type="text/x-template" id="task-template">
<div>
<EditTask v-model="listLocal"></EditTask>
</div>
</script>
If EditTask emits a change it will appropriately call set() on listLocal and thereby propagate the event to the top level. Similarly, the EditTask component could also call other child components (such as form elements) using v-model.
Vue just warns you: you change the prop in the component, but when parent component re-renders, "list" will be overwritten and you lose all your changes. So it is dangerous to do so.
Use computed property instead like this:
Vue.component('task', {
template: '#task-template',
props: ['list'],
computed: {
listJson: function(){
return JSON.parse(this.list);
}
}
});
If you're using Lodash, you can clone the prop before returning it. This pattern is helpful if you modify that prop on both the parent and child.
Let's say we have prop list on component grid.
In Parent Component
<grid :list.sync="list"></grid>
In Child Component
props: ['list'],
methods:{
doSomethingOnClick(entry){
let modifiedList = _.clone(this.list)
modifiedList = _.uniq(modifiedList) // Removes duplicates
this.$emit('update:list', modifiedList)
}
}
Props down, events up. That's Vue's Pattern. The point is that if you try to mutate props passing from a parent. It won't work and it just gets overwritten repeatedly by the parent component. Child component can only emit an event to notify parent component to do sth. If you don't like these restrict, you can use VUEX(actually this pattern will suck in complex components structure, you should use VUEX!)
You should not change the props's value in child component.
If you really need to change it you can use .sync.
Just like this
<your-component :list.sync="list"></your-component>
Vue.component('task', {
template: '#task-template',
props: ['list'],
created() {
this.$emit('update:list', JSON.parse(this.list))
}
});
new Vue({
el: '.container'
})
According to the VueJs 2.0, you should not mutate a prop inside the component. They are only mutated by their parents. Therefore, you should define variables in data with different names and keep them updated by watching actual props.
In case the list prop is changed by a parent, you can parse it and assign it to mutableList. Here is a complete solution.
Vue.component('task', {
template: ´<ul>
<li v-for="item in mutableList">
{{item.name}}
</li>
</ul>´,
props: ['list'],
data: function () {
return {
mutableList = JSON.parse(this.list);
}
},
watch:{
list: function(){
this.mutableList = JSON.parse(this.list);
}
}
});
It uses mutableList to render your template, thus you keep your list prop safe in the component.
The answer is simple, you should break the direct prop mutation by assigning the value to some local component variables(could be data property, computed with getters, setters, or watchers).
Here's a simple solution using the watcher.
<template>
<input
v-model="input"
#input="updateInput"
#change="updateInput"
/>
</template>
<script>
export default {
props: {
value: {
type: String,
default: '',
},
},
data() {
return {
input: '',
};
},
watch: {
value: {
handler(after) {
this.input = after;
},
immediate: true,
},
},
methods: {
updateInput() {
this.$emit('input', this.input);
},
},
};
</script>
It's what I use to create any data input components and it works just fine. Any new data sent(v-model(ed)) from parent will be watched by the value watcher and is assigned to the input variable and once the input is received, we can catch that action and emit input to parent suggesting that data is input from the form element.
do not change the props directly in components.if you need change it set a new property like this:
data() {
return {
listClone: this.list
}
}
And change the value of listClone.
I faced this issue as well. The warning gone after i use $on and $emit.
It's something like use $on and $emit recommended to sent data from child component to parent component.
one-way Data Flow,
according to https://v2.vuejs.org/v2/guide/components.html, the component follow one-Way
Data Flow,
All props form a one-way-down binding between the child property and the parent one, when the parent property updates, it will flow down to the child but not the other way around, this prevents child components from accidentally mutating the parent's, which can make your app's data flow harder to understand.
In addition, every time the parent component is updates all props
in the child components will be refreshed with the latest value. This means you should not attempt to mutate a prop inside a child component. If you do .vue will warn you in the
console.
There are usually two cases where it’s tempting to mutate a prop:
The prop is used to pass in an initial value; the child component wants to use it as a local data property afterwards.
The prop is passed in as a raw value that needs to be transformed.
The proper answer to these use cases are:
Define a local data property that uses the prop’s initial value as its initial value:
props: ['initialCounter'],
data: function () {
return { counter: this.initialCounter }
}
Define a computed property that is computed from the prop’s value:
props: ['size'],
computed: {
normalizedSize: function () {
return this.size.trim().toLowerCase()
}
}
If you want to mutate props - use object.
<component :model="global.price"></component>
component:
props: ['model'],
methods: {
changeValue: function() {
this.model.value = "new value";
}
}
I want to give this answer which helps avoid using a lot of code, watchers and computed properties. In some cases this can be a good solution:
Props are designed to provide one-way communication.
When you have a modal show/hide button with a prop the best solution to me is to emit an event:
<button #click="$emit('close')">Close Modal</button>
Then add listener to modal element:
<modal :show="show" #close="show = false"></modal>
(In this case the prop show is probably unnecessary because you can use an easy v-if="show" directly on the base-modal)
You need to add computed method like this
component.vue
props: ['list'],
computed: {
listJson: function(){
return JSON.parse(this.list);
}
}
Vue.component('task', {
template: '#task-template',
props: ['list'],
computed: {
middleData() {
return this.list
}
},
watch: {
list(newVal, oldVal) {
console.log(newVal)
this.newList = newVal
}
},
data() {
return {
newList: {}
}
}
});
new Vue({
el: '.container'
})
Maybe this will meet your needs.
Vue3 has a really good solution. Spent hours to reach there. But it worked really good.
On parent template
<user-name
v-model:first-name="firstName"
v-model:last-name="lastName"
></user-name>
The child component
app.component('user-name', {
props: {
firstName: String,
lastName: String
},
template: `
<input
type="text"
:value="firstName"
#input="$emit('update:firstName',
$event.target.value)">
<input
type="text"
:value="lastName"
#input="$emit('update:lastName',
$event.target.value)">
`
})
This was the only solution which did two way binding. I like that first two answers were addressing in good way to use SYNC and Emitting update events, and compute property getter setter, but that was heck of a Job to do and I did not like to work so hard.
Vue.js props are not to be mutated as this is considered an Anti-Pattern in Vue.
The approach you will need to take is creating a data property on your component that references the original prop property of list
props: ['list'],
data: () {
return {
parsedList: JSON.parse(this.list)
}
}
Now your list structure that is passed to the component is referenced and mutated via the data property of your component :-)
If you wish to do more than just parse your list property then make use of the Vue component' computed property.
This allow you to make more in depth mutations to your props.
props: ['list'],
computed: {
filteredJSONList: () => {
let parsedList = JSON.parse(this.list)
let filteredList = parsedList.filter(listItem => listItem.active)
console.log(filteredList)
return filteredList
}
}
The example above parses your list prop and filters it down to only active list-tems, logs it out for schnitts and giggles and returns it.
note: both data & computed properties are referenced in the template the same e.g
<pre>{{parsedList}}</pre>
<pre>{{filteredJSONList}}</pre>
It can be easy to think that a computed property (being a method) needs to be called... it doesn't
For when TypeScript is your preferred lang. of development
<template>
<span class="someClassName">
{{feesInLocale}}
</span>
</template>
#Prop({default: 0}) fees: any;
// computed are declared with get before a function
get feesInLocale() {
return this.fees;
}
and not
<template>
<span class="someClassName">
{{feesInLocale}}
</span>
</template>
#Prop() fees: any = 0;
get feesInLocale() {
return this.fees;
}
Assign the props to new variable.
data () {
return {
listClone: this.list
}
}
Adding to the best answer,
Vue.component('task', {
template: '#task-template',
props: ['list'],
data: function () {
return {
mutableList: JSON.parse(this.list);
}
}
});
Setting props by an array is meant for dev/prototyping, in production make sure to set prop types(https://v2.vuejs.org/v2/guide/components-props.html) and set a default value in case the prop has not been populated by the parent, as so.
Vue.component('task', {
template: '#task-template',
props: {
list: {
type: String,
default() {
return '{}'
}
}
},
data: function () {
return {
mutableList: JSON.parse(this.list);
}
}
});
This way you atleast get an empty object in mutableList instead of a JSON.parse error if it is undefined.
YES!, mutating attributes in vue2 is an anti-pattern. BUT...
Just break the rules by using other rules, and go forward!
What you need is to add .sync modifier to your component attribute in the parent scope.
<your-awesome-components :custom-attribute-as-prob.sync="value" />
Below is a snack bar component, when I give the snackbar variable directly into v-model like this if will work but in the console, it will give an error as
Avoid mutating a prop directly since the value will be overwritten whenever the parent component re-renders. Instead, use a data or computed property based on the prop's value.
<template>
<v-snackbar v-model="snackbar">
{{ text }}
</v-snackbar>
</template>
<script>
export default {
name: "loader",
props: {
snackbar: {type: Boolean, required: true},
text: {type: String, required: false, default: ""},
},
}
</script>
Correct Way to get rid of this mutation error is use watcher
<template>
<v-snackbar v-model="snackbarData">
{{ text }}
</v-snackbar>
</template>
<script>
/* eslint-disable */
export default {
name: "loader",
data: () => ({
snackbarData:false,
}),
props: {
snackbar: {type: Boolean, required: true},
text: {type: String, required: false, default: ""},
},
watch: {
snackbar: function(newVal, oldVal) {
this.snackbarData=!this.snackbarDatanewVal;
}
}
}
</script>
So in the main component where you will load this snack bar you can just do this code
<loader :snackbar="snackbarFlag" :text="snackText"></loader>
This Worked for me
Vue.js considers this an anti-pattern. For example, declaring and setting some props like
this.propsVal = 'new Props Value'
So to solve this issue you have to take in a value from the props to the data or the computed property of a Vue instance, like this:
props: ['propsVal'],
data: function() {
return {
propVal: this.propsVal
};
},
methods: {
...
}
This will definitely work.
In addition to the above, for others having the following issue:
"If the props value is not required and thus not always returned, the passed data would return undefined (instead of empty)". Which could mess <select> default value, I solved it by checking if the value is set in beforeMount() (and set it if not) as follows:
JS:
export default {
name: 'user_register',
data: () => ({
oldDobMonthMutated: this.oldDobMonth,
}),
props: [
'oldDobMonth',
'dobMonths', //Used for the select loop
],
beforeMount() {
if (!this.oldDobMonth) {
this.oldDobMonthMutated = '';
} else {
this.oldDobMonthMutated = this.oldDobMonth
}
}
}
Html:
<select v-model="oldDobMonthMutated" id="dob_months" name="dob_month">
<option selected="selected" disabled="disabled" hidden="hidden" value="">
Select Month
</option>
<option v-for="dobMonth in dobMonths"
:key="dobMonth.dob_month_slug"
:value="dobMonth.dob_month_slug">
{{ dobMonth.dob_month_name }}
</option>
</select>
I personally always suggest if you are in need to mutate the props, first pass them to computed property and return from there, thereafter one can mutate the props easily, even at that you can track the prop mutation , if those are being mutated from another component too or we can you watch also .
Because Vue props is one way data flow, This prevents child components from accidentally mutating the parent’s state.
From the official Vue document, we will find 2 ways to solve this problems
if child component want use props as local data, it is best to define a local data property.
props: ['list'],
data: function() {
return {
localList: JSON.parse(this.list);
}
}
The prop is passed in as a raw value that needs to be transformed. In this case, it’s best to define a computed property using the prop’s value:
props: ['list'],
computed: {
localList: function() {
return JSON.parse(this.list);
},
//eg: if you want to filter this list
validList: function() {
return this.list.filter(product => product.isValid === true)
}
//...whatever to transform the list
}
You should always avoid mutating props in vue, or any other framework. The approach you could take is copy it into another variable.
for example.
// instead of replacing the value of this.list use a different variable
this.new_data_variable = JSON.parse(this.list)
A potential solution to this is using global variables.
import { Vue } from "nuxt-property-decorator";
export const globalStore = new Vue({
data: {
list: [],
},
}
export function setupGlobalsStore() {
Vue.prototype.$globals = globalStore;
}
Then you would use:
$globals.list
Anywhere you need to mutate it or present it.

vue.js list ( template ) binding not updating when changing data from directive

First of all : I'm using laravel spark and the given setup of vue that comes with spark.
I have a "home" component with the prop "custom". Within custom there's a "passwords" array. (Entry added by code of directive, it's initialized empty)
My component ( alist) which should be bound against the data
<template id="passwords-list-template">
<div class="password" v-for="password in list">
<ul>
<li>{{ password.name }}</li>
<li>{{ password.description }}</li>
</ul>
</div>
</template>
<script>
export default {
template: '#passwords-list-template',
props: ['list'],
};
</script>
Usage
<passwords-list :list="custom.passwords"></passwords-list>
Using vue devtools I can see that my data is updating, however my list is not. Also other bindings like
<div v-show="custom.passwords.length > 0">
Are not working ...
UPDATE : Parent component (Home)
Vue.component('home', {
props: ['user', 'custom'],
ready : function() {
}
});
Usage
<home :user="user" :custom="spark.custom" inline-template>
Update 2: I played around a little bit using jsfiddle. It seems like changing the bound data object using $root works fine for me when using a method of a component. However it does not work when trying to access it using a directive
https://jsfiddle.net/wa21yho2/1/
There were a lot of errors in your Vue code. First of all, your components where isolated, there wasn't an explicit parent-child relationship.Second, there were errors in the scope of components, you were trying to set data of the parent in the child, also, you were trying to set the value of a prop, and props are by default readonly, you should have written a setter function or change them to data. And finally, I can't understand why were you trying to use a directive if there were methods and events involve?
Anyway, I rewrote your jsfiddle, I hope that you find what you need there. The chain is Root > Home > PasswordList. And the data is in the root but modified in home, the last component only show it. the key here are twoWay properties, otherwise you wouldn't be able to modify data through properties.
Here is a snippet of code
Home
var Home = Vue.component('home', {
props: {
user: {
default: ''
},
custom: {
twoWay: true
}
},
components: {
passwordList: PasswordList
},
methods: {
reset: function () {
this.custom.passwords = [];
}
}
});
// template
<home :custom.sync="spark.custom" inline-template>
{{custom | json}}
<button #click="reset">
reset in home
</button>
<password-list :list="custom.passwords"></password-list>
<password-list :list="custom.passwords"></password-list>
</home>
Here is the full jsfiddle

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