I'm making a todo app in vue.js which has a component TodoItem
<template>
<div class="todo-item" v-bind:class="{'is-completed':todo.completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{todo.task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["todo"],
methods: {
markCompleted() {
this.todo.completed = true
},
},
};
</script>
todo prop that I'm passing:
{
id:1,
task:'todo 1',
completed:false
}
but it is throwing an error error Unexpected mutation of "todo" prop
Method 1 (Vue 2.3.0+) - From your parent component, you can pass prop with sync modifier
Parent Component
<TodoItem v-for="todo in todoList" :key="todo.id" todo_prop.sync="todo">
Child Component
<template>
<div class="todo-item" v-bind:class="{'is-completed':todo.completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{todo.task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["todo_prop"],
data() {
return {
todo: this.todo_prop
}
},
methods: {
markCompleted() {
this.todo.completed = true
},
},
};
</script>
Method 2 - Pass props from parent component without sync modifier and emit an event when the value changed. For this method, everything else is similar as well. Just need to emit an event when the todo item changed to completed.
The code is untested. Apologies if anything does not work.
What happen ? : Mutating a prop locally is now considered an anti-pattern, e.g. declaring a prop and then setting this.myProp = 'someOtherValue' in the component. Due to the new rendering mechanism, whenever the parent component re-renders, the child component’s local changes will be overwritten.
Solution : You can storage it as local data.
export default {
name: "TodoItem",
props: ["todo"],
data() {
return {
todoLocal: this.todo,
};
},
methods: {
markComplete() {
this.todoLocal.completed = !this.todoLocal.completed;
},
},
};
For me to fix this problem I store props in todos data im watching brad vue tutorials and i get this error this is my actual codes and its working.
<template>
<div class="todo-item" v-bind:class="{ 'is-complete': todo.completed }">
<p>
<input
type="checkbox"
v-on:change="markComplete(todo.completed)"
v-bind:checked="todo.completed"
/>
{{ todo.title }}
<!-- <button #click="$emit('del-todo', todo.id)" class="del">x</button> -->
</p>
</div>
</template>
<script>
export default {
name: 'TodoItem',
props: ['todo'],
data() {
return {
todos: this.todo,
}
},
methods: {
markComplete(isComplete) {
this.todos.completed = !isComplete
},
},
}
</script>
<style scoped>
.todo-item {
background: #f4f4f4;
padding: 10px;
border-bottom: 1px #ccc dotted;
}
.is-complete {
text-decoration: line-through;
}
.del {
background: #ff0000;
color: #fff;
border: none;
padding: 5px 9px;
border-radius: 50%;
cursor: pointer;
float: right;
}
</style>
One of the core principles of VueJS is that child components never mutate a prop.
All props form a one-way-down binding between the child property and the parent one: when the parent property updates, it will flow down to the child, but not the other way around.
If you wish to have the child component update todo.completed, you have two choices:
Use .sync modifier (Recommended)
This approach will require a bit of change to your props. You can read more about it here.
Parent component
<template>
<div>
...
<todo-item :task="nextTodo.task" :completed.sync="nextTodo.completed"/>
</div>
</template>
Child component
<template>
<div class="todo-item" v-bind:class="{'is-completed':completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["task", "completed"],
methods: {
markCompleted() {
this.$emit('update:completed', true)
},
},
};
</script>
Use a custom event
Vue allows you set up listeners in your parent for events that the child will emit. Your child component can use this mechanism to ask the parent to change things. In fact, the above .sync modifier is doing exactly this behind the scenes.
Parent component
<template>
<div>
...
<todo-item :todo="nextTodo" #set-completed="$value => { nextTodo.completed = $value }/>
</div>
</template>
Child component
<template>
<div class="todo-item" v-bind:class="{'is-completed':todo.completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{todo.task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["todo"],
methods: {
markCompleted() {
this.$emit('set-completed', true)
},
},
};
</script>
You can't change a prop from inside a component - they are meant to be set by the parent only. It's a one-directional communication path.
You can try one of two things - either move your logic for detecting a todo has been completed to the parent, or feed the prop into a new variable in the data() lifecycle hook (this will only happen when the component is loaded for the first time, so you won't be able to update from outside the component, if that's important for your use case).
The canonical way to achieve n-deep prop binding in Vue 3 is to wrap your prop with a simple computed property. This is an example of a component that will communicate changes to it's selected property to it's parent--who is ultimately responsible for storing the state.
<template>
<!-- In this example my-child-component also has a "selected" prop -->
<my-child-component v-model:selected="syncSelectedId" />
</template>
<script lang="ts">
export default defineComponent({
components: { MyChildComponent },
props: {
selected: {
type: String,
required: true,
}
},
emits: ['update:selected'],
setup(props, context) {
const syncSelectedId = computed<string>({
get() {
return props.selected;
},
set(newVal: string) {
context.emit('update:selected', newVal);
},
});
return {
syncSelectedId,
}
}
});
So to re-iterate: With this strategy the highest level parent is the holder of the state. The code above assumes that there is a parent component in the hierarchy (so this component is just a "middle-man").
Then my-child-component can simply emit its own update:selected event to cause the state to change. That child will be updated appropriately through it's prop after the emit event causes the parent chain to propagate that change up (through emits) and then back down the component hierarchy (through props).
If you wanted to you could modify the code above to make it the "owner" of the state:
<template>
<my-child-component v-model:selected="selected" />
</template>
<script lang="ts">
export default defineComponent({
components: { MyChildComponent },
setup(props, context) {
const selected = ref('');
return {
selected,
}
}
});
And now of course you won't run into the "Unexpected mutation of X prop" error.
Another option is to have a prop that serves as a "default value" for a given state:
<template>
<my-child-component v-model:selected="selected" />
</template>
<script lang="ts">
export default defineComponent({
components: { MyChildComponent },
props: {
defaultSelected: {
type: String,
required: false,
default: ''
}
},
setup(props, context) {
const selected = ref(props.defaultSelected);
return {
selected,
}
}
});
And in this code above keep in mind that selected will NOT change if defaultSelected changes after the component has been initialized.
And lastly it's worth noting that you could write more sophisticated code to detect if a property is supplied--and if not use an internal state variable to store the value. I use this pattern for re-usable components that could be embedded in places where the parent wants to control the state OR in places where the parent is happy to delegate the storage of the state to the child:
<template>
<!-- In this example my-child-component also has a "selected" prop -->
<my-child-component v-model:selected="syncSelectedId" />
</template>
<script lang="ts">
export default defineComponent({
components: { MyChildComponent },
props: {
selected: {
type: String,
required: false,
default: null // Important: parent MUST pass non-null value if it wants to control state
}
},
emits: ['update:selected'],
setup(props, context) {
// This is state storage used if prop.selected is not provided
const _selected = ref('');
const syncSelectedId = computed<string>({
get() {
return props.selected === null ? _selected.value : props.selected;
},
set(newVal: string) {
if (props.selected !== null) {
// Using prop.selected as the driving model...
if (newVal !== props.selected) {
// We need to set to empty string (never null)
context.emit('update:selectedId', (newVal == null ? '' : newVal));
}
} else { // Storing selection state with _selectedId
if (newVal !== _selected.value) {
_selected.value = newVal == null ? '' : newVal;
context.emit('update:selected', _selected);
}
}
},
});
return {
syncSelectedId,
}
}
});
This last example is tricky... it gives special meaning to null and requires that you be very mindful of potential values of your state. In my example empty string is my representation for "no selection" and null is used as a flag for "no parent model of this state".
Mainly, property mutation is now deprecated and parent properties are overwritten when the parent component renders its DOM.
Here's the official documentation about it. We can still achieve this in multiple possible ways. Through a data property, a computed property, and component events.
When we want to pass this value back to the parent component as well as the nested child component of the current child component, using a data property would be useful as shown in the following example.
Example:
Calling your child component from the parent component like this.
Parent component:
<template>
<TodoItem :todoParent="todo" />
</template>
<script>
export default {
data() {
return {
todo: {
id:1,
task:'todo 1',
completed:false
}
};
}
}
</script>
Child component:
<template>
<div class="todo-item" v-bind:class="{'is-completed':todo.completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{todo.task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["todoParent"],
data() {
return {
todo: this.todoParent,
};
},
methods: {
markCompleted() {
this.todo.completed = true
},
},
};
</script>
Even you can pass this property to the nested child component and it won't give this error/warning.
Other use cases when you only need this property sync between parent and child component. It can be achieved using the sync modifier from Vue. v-model can also be useful. Many other examples are available in this question thread.
Example2: using component events.
We can emit the event from the child component as below.
Parent component:
<template>
<TodoItem :todo="todo" #markCompletedParent="markCompleted" />
</template>
<script>
export default {
data() {
return {
todo: {
id:1,
task:'todo 1',
completed:false
}
};
},
methods: {
markCompleted() {
this.todo.completed = true
},
}
}
</script>
Child component:
<template>
<div class="todo-item" v-bind:class="{'is-completed':todo.completed}">
<p>
<input type="checkbox" #change="markCompleted" />
{{todo.task}}
<button class="del">x</button>
</p>
</div>
</template>
<script>
export default {
name: "TodoItem",
props: ["todo"],
methods: {
markCompleted() {
this.$emit('markCompletedParent', true)
},
}
};
</script>
While you can still custom-bind events to handle this, .sync property extensions are considered deprecated. In Vue3 (at least) you can and usually should use the v-model:property declaration, similar to how you bind the property to the actual input. You just need to bind the inner input with :value and have it emit a matching update:property
<!-- CustomInput.vue -->
<script setup>
defineProps(['modelValue'])
defineEmits(['update:modelValue'])
</script>
<template>
<input
:value="modelValue"
#input="$emit('update:modelValue', $event.target.value)"
/>
</template>
And use thusly:
<CustomInput v-model="searchText" />
Imagine I have a order form with 3 stages - Personal details, Order details, payment.
I want to toggle the next component from within the previous one (hoping to adjust the value of 'step')
<Component1 v-if="step = 1"></Component1>
<Component2 v-else-if="step = 2"></Component2>
<Component3 v-else></Component3>
So, with those on my view, is it possible for me to pass the value of 'step' in to component1 and do something like
<button v-on:click="step = 2">
Submit
</button>
then on that click, update the value of step on my main view (with the 3 components) and with that, hide my first completed component and displaying the second?
Thanks for any insight!
Why you dont use dynamic components?
On your parent component you listen to the event that changes yours step, i named it here nextStep. This event triggers the method changeStep that changes the component name.
<component #nextStep="changeStep" :name="selectedComponent"></component>
import component1 from "../components/component1.vue";
import component2 from "../components/component2.vue";
import component3 from "../components/component3.vue";
export default {
data(){
return {
selectedComponent: "component1"
}
}
},
methods: {
changeStep(step){
this.selectedComponent = step;
}
},
components: {
component1,
component2,
component3
}
//in the child component
method: {
changeStep(){
this.$emit("nextStep", "component2");
}
}
This is how you emit the event to the parent to change the component
You just need to change the property selectedComponent to the component name you want and it will change it
If you are still searching for the answer. This first code to add as your parent component.
<template>
<main>
<component #nextStep="changeStep" v-bind:is="selectedComponent"></component>
</main>
</template>
<script lang="ts">
import Setup1 from '#/components/Setup/Setup1.vue';
import Setup2 from '#/components/Setup/Setup2.vue';
import Setup3 from '#/components/Setup/Setup3.vue';
export default {
name: "SetupView",
components: {
Setup1, Setup2, Setup3
},
data() {
return {
selectedComponent: "Setup1"
}
}, methods: {
changeStep(step: string) {
this.selectedComponent = step;
}
},
}
</script>
Add the code below as the child component .
<template>
<div>
Setup step 1
<button #click="changeStep">Next step</button>
</div>
</template>
<script lang="ts">
export default {
name: "setup1",
methods: {
changeStep() {
this.$emit("nextStep", "Setup2");
}
}
}
</script>
v-bind:is="selectedComponent"
I have the following setup:
CustomForm.vue
<template>
<div>
<input v-model="field1" >
<input v-model="field2" >
</div>
</template>
<script>
export default {
data () {
return {
field1: '',
field2: '',
}
}
}
</script>
Parent.vue
<template>
<div>
<child>
<template>
<custom-form />
</template>
</child>
</div>
</template>
<script>
import Child from ...
import CustomForm from ...
</script>
Child.vue
<template>
<div>
<button #click="click" />
<grand-child>
<template>
<slot></slot>
</template>
</grand-child>
</div>
</template>
<script>
import GrandChild from...
export default {
methods: {
click: function () {
var data = ... // get form data
// do something with data then $emit
this.$emit('custom-click', data)
}
}
}
}
</script>
GrandChild.vue
<template>
<div v-for="(item, index) in list" :key="index" >
<input ...>
<input ...>
<slot></slot>
</div>
</template>
Basically I have a CustomForm, I want to pass the form to GrandChild.vue from Parent.vue, but the issue is I don't know how do I retrieve CustomForm data (field1, field2) in Child.vue ie how do I get CustomForm value from click method in Child.vue? Thanks
Instead of trying to extract data from a slot, there are other approaches. One solution is to use Vue's provide/inject feature to inject the form's data.
First, setup CustomForm to allow v-model to capture the form data in Parent:
Upon submitting the form in CustomForm, emit the input event with the form's data.
Add a value prop, as required for `v-model.
CustomForm.vue:
<template>
<form #submit.prevent="submit"> <!-- (1) -->
</form>
</template>
<script>
export default {
props: ['value'], // <-- (2)
methods: {
submit(e) { // <-- (1)
const form = e.target
const formData = {}
for (const [key, value] of new FormData(form).entries()) {
formData[key] = value
}
this.$emit('input', formData)
}
}
}
</script>
Then Parent can bind the form data:
Define parentForm in Parent's data as an object with a subproperty (e.g., parentForm.data).
Bind that subproperty to CustomForm's v-model.
Parent.vue:
<template>
<child>
<custom-form v-model="parentForm.data" /> <!-- (4) -->
</child>
</template>
<script>
export default {
data() {
return {
parentForm: { // <-- (3)
data: {}
}
};
}
}
</script>
Now, Parent can provide form:
Declare a provide method that returns an object with a form subproperty.
Set that property's value to the parentForm property previously declared in (3).
Parent.vue:
export default {
provide() { // <-- (5)
return {
form: this.parentForm // <-- (6)
}
}
}
...and Child or GrandChild can inject form:
Declare an inject property, whose value is a string array containing form (subproperty name from (5)).
GrandChild.vue:
export default {
inject: ['form'] // <-- (7)
}
demo
Is it possible to bind a prop to a function?
In my example below I’m trying to get a value from a function in the main App.vue and pass it as a prop to the child component customComponent.
e.g. (this example doesn’t work)
App.vue
import customComponent from ‘./custom-component.vue'
<template>
<custom-component
v-bind:myValue="geMyValue()"
></custom-component>
</template>
<script>
export default {
name: "Item",
methods: {
getMyValue: function() {
return 1+3;
}
}
}
</script>
customComponent.vue
<template>
<h3 class="some-custom-layout">custom component</h3>
<input type="button" #click="sendMyValue()" />
</template>
<script>
export default {
name: “custom",
props: ['myValue']
methods: {
sendMyValue: function() {
console.log(this.myValue);
}
}
}
</script>
It's possible, but probably it would be better to use computed properties, if you are going to return value:
<template>
<custom-component
v-bind:myValue="myValue"
></custom-component>
</template>
<script>
export default {
name: "Item",
computed: {
myValue: function() {
return 1+3;
}
}
}
</script>
https://v2.vuejs.org/v2/guide/computed.html
I'm using vue, version 2.5.8
I want to reload child component's, or reload parent and then force children components to reload.
I was trying to use this.$forceUpdate() but this is not working.
Do You have any idea how to do this?
Use a :key for the component and reset the key.
See https://michaelnthiessen.com/force-re-render/
Add key to child component, then update the key in parent. Child component will be re-created.
<childComponent :key="childKey"/>
If the children are dynamically created by a v-for or something, you could clear the array and re-assign it, and the children would all be re-created.
To simply have existing components respond to a signal, you want to pass an event bus as a prop, then emit an event to which they will respond. The normal direction of events is up, but it is sometimes appropriate to have them go down.
new Vue({
el: '#app',
data: {
bus: new Vue()
},
components: {
child: {
template: '#child-template',
props: ['bus'],
data() {
return {
value: 0
};
},
methods: {
increment() {
this.value += 1;
},
reset() {
this.value = 0;
}
},
created() {
this.bus.$on('reset', this.reset);
}
}
}
});
<script src="//cdnjs.cloudflare.com/ajax/libs/vue/2.4.2/vue.min.js"></script>
<div id="app">
<child :bus="bus">
</child>
<child :bus="bus">
</child>
<child :bus="bus">
</child>
<button #click="() => bus.$emit('reset')">Reset</button>
</div>
<template id="child-template">
<div>
{{value}} <button #click="increment">More!</button>
</div>
</template>
I'm using directive v-if which is responsible for conditional rendering. It only affects reloading HTML <template> part. Sections created(), computed are not reloaded. As I understand after framework load components reloading it is not possible. We can only re render a <template>.
Rerender example.
I have a Child.vue component code:
<template>
<div v-if="show">
Child content to render
{{ callDuringReRender() }}
</div>
</template>
<script>
export default {
data() {
return {
show: true
}
}
,
methods: {
showComponent() {
this.show = true
},
hideComponent() {
this.show = false
},
callDuringReRender() {
console.log("function recall during rendering")
}
}
}
</script>
In my Parent.vue component I can call child methods and using it's v-if to force the child rerender
<template>
<div>
<input type="button"
value="ReRender the child"
#click="reRenderChildComponent"/>
<child ref="childComponent"></child>
</div>
</template>
<script>
import Child from './Child.vue'
export default {
methods: {
reRenderChildComponent(){
this.$refs.childComponent.hideComponent();
this.$refs.childComponent.showComponent()
}
},
components: {
Child
}
}
</script>
After clicking a button in console You will notice message "function recall during rendering" informing You that component was rerendered.
This example is from the link that #sureshvv shared
import Vue from 'vue';
Vue.forceUpdate();
// Using the component instance
export default {
methods: {
methodThatForcesUpdate() {
// ...
this.$forceUpdate(); // Notice we have to use a $ here
// ...
}
}
}
I've found that when you want the child component to refresh you either need the passed property to be output in the template somewhere or be accessed by a computed property.
<!-- ParentComponent -->
<template>
<child-component :user="userFromParent"></child-component>
</template>
<!-- ChildComponent -->
<template>
<!-- 'updated' fires if property 'user' is used in the child template -->
<p>user: {{ user.name }}
</template>
<script>
export default {
props: {'user'},
data() { return {}; }
computed: {
// Or use a computed property if only accessing it in the script
getUser() {
return this.user;
}
}
}
</script>