Develop Reference

Binding child input :value to the parent prop

I try to bind child input value to the parent value. I pass value searchText from a Parent component to a Child component as prop :valueProp. There I assign it to property value: this.valueProp and bind input:
<input type="text" :value="value" #input="$emit('changeInput', $event.target.value)" />
The problem is that input doesn't work with such setup, nothing displays in input, but parent searchText and valueProp in child update only with the last typed letter; value in child doesn't update at all, though it is set to equal to searchText.
If I remove :value="value" in input, all will work fine, but value in child doesn't get updated along with parent's searchText.
I know that in such cases it's better to use v-model, but I want to figure out the reason behind such behavior in that case.
I can't understand why it works in such way and value in child component doesn't update with parent's searchText. Can you please explain why it behaves in that way?
Link to Sanbox: Sandbox
Parent:
<template>
<div>
<Child :valueProp="searchText" #changeInput="changeInput" />
<p>parent {{ searchText }}</p>
</div>
</template>
<script>
import Child from "./Child.vue";
export default {
name: "Parent",
components: { Child },
data() {
return {
searchText: "",
};
},
methods: {
changeInput(data) {
console.log(data);
this.searchText = data;
},
},
};
</script>
Child:
<template>
<div>
<input type="text" :value="value" #input="$emit('changeInput', $event.target.value)" />
<p>value: {{ value }}</p>
<p>child: {{ valueProp }}</p>
</div>
</template>
<script>
export default {
emits: ["changeInput"],
data() {
return {
value: this.valueProp,
};
},
props: {
valueProp: {
type: String,
required: true,
},
},
};
</script>

You set the value in your Child component only once by instantiating.
In the data() you set the initial value of your data properties:
data() {
return {
value: this.valueProp,
};
},
Since you don't use v-model, the value will never be updated.
You have the following options to fix it:
The best one is to use v-model with value in the Child.vue
<input
type="text"
v-model="value"
update value using watcher
watch: {
valueProp(newValue) {
this.value = newValue;
}
},
use a computed property for value instead of data property
computed: {
value() {return this.valueProp;}
}
Respect for creating the sandbox!

You are overwriting the local value every time the value changes
data() {
return {
value: this.valueProp, // Don't do this
};
},
Bind directly to the prop:
<input ... :value="valueProp" ... />

VueJs 3 - Custom Input Component

I'm trying to build a custom HTML <input> component for VueJS3. I've been following this tutorial:
https://dev.to/viniciuskneves/vue-custom-input-bk8
So far I managed to get the CustomInput.vue component to work and emit the modified value back to the parent App.Vue.
<template>
<label>
{{ label }}
<input type="text" :name="name" :value="value" #input="onInput" #change="onChange" />
</label>
</template>
<script>
export default {
name: 'CustomInput',
props: {
label: {
type: String,
required: true,
},
value: {
type: String,
required: true,
},
},
computed: {
name() {
return this.label.toLowerCase();
},
},
methods: {
onInput(event) {
this.$emit('input', event.target.value);
},
onChange(event) {
this.$emit('change', event.target.value);
},
},
}
</script>
What I don't understand is - how will the emitted events be detected by the parent App.vue component? I can't see it happens, and I can't find it in the tutorial.
My App.Vue looks like this:
<template>
<custom-input :label="'Name'" :value="name"></custom-input>
<div>{{ name }}</div>
</template>
<script>
import customInput from "./components/CustomInput.vue";
export default {
components: { customInput },
name: "App",
data: function () {
return {
name: "",
};
},
mounted() {
this.name = "Thomas";
},
};
</script>
Thanks in advance for any help :-)

This tutorial is for Vue 2 - for Vue 3 there is another tutorial (https://www.webmound.com/use-v-model-custom-components-vue-3/)
Emitting input event works in Vue 2 only - for Vue 3 you will have to emit update:modelValue and also use modelValue as a prop instead of just value.

You can do it right in your template.
<custom-input :label="'Name'" :value="name" #change='name=$event' #input='name=$event'></custom-input>
You can also use a method or computed with setter as well.

Error: "Error in v-on handler: "TypeError: this.filter is undefined"" in a list rendering in vue?

I am trying to build a component that creates filter buttons and then sends the type attribute in the filters object through the event bus to be handled elsewhere in my app. However, when I added the array of objects (filters) in the data section, I am getting an error of this.filter is not defined when I click on a button.
I would like to keep the filters array in this component because I am also trying to dynamically change the active class to whichever button has been clicked.
Am I missing something that has to do with props? Why am I unable to display the buttons when the data and v-for was on another component? These were the questions I have been asking myself in order of solving this issue.
<template>
<div>
<button
v-for="(filter, index) in filters"
:key="index"
:class="{ active: index === activeItem }"
#click="emitFilter(), selectItem(index)"
:filter="filter"
>
{{ filter.name }}
</button>
</div>
</template>
<script>
import EventBus from '#/components/EventBus'
export default {
props: {
filter: { type: String }
},
data() {
return {
activeItem: 0,
filterResult: '',
filters: [
{ name: 'All', type: 'all' },
{ name: 'Holidays', type: 'holiday' },
{ name: 'Seasons', type: 'season' },
{ name: 'Events', type: 'custom' }
]
}
},
methods: {
emitFilter() {
this.filterResult = this.filter
EventBus.$emit('filter-catagories', this.filterResult)
},
selectItem(index) {
this.activeItem = index
}
}
}
</script>
My button component is used in a filters component
<template>
<div>
<span>filters</span>
<FilterBtn />
</div>
</div>
</template>
<script>
import FilterBtn from '#/components/FilterBtn'
export default {
components: {
FilterBtn
}
// data() {
// return {
// filters: [
// { name: 'All', type: 'all' },
// { name: 'Holidays', type: 'holiday' },
// { name: 'Seasons', type: 'season' },
// { name: 'Events', type: 'custom' }
// ]
// }
// }
}
</script>
As you can see, the commented section is where I had my filters originally, but I had to move them to the button component in order to add the active class.

I'm assuming you were actually trying to access the filter iterator of v-for="(filter, index) in filters" from within emitFilter(). For this to work, you'd need to pass the filter itself in your #click binding:
<button v-for="(filter, index) in filters"
#click="emitFilter(filter)">
Then, your handler could use the argument directly:
export default {
methods: {
emitFilter(filter) {
this.filterResult = filter
//...
}
}
}

You are passing a prop called filter typed string to your component. When you output {{ filter.name }} you are actually referring to this property instead of the variable filter you create within the v-for loop.
Unless you passed a property called "filter" to your component, this property will be undefined. Therefore outputting filter.name will result in this error message.

Yea you dont pass an prop to your component thats why its undefined.
<FilterBtn filter="test" />
Here i pass an prop named filter with the value of test.
Sure you could pass dynamic props. Just bind it.
<FilterBtn :filter="yourData" />
I need to ask: Are you passing an object or an string?
Because you defined your prop to be a string, but you actually use it as an object
{{ filter.name }}
Maybe you should also set the type to Object.
props: {
filter: { type: Object }
},

Why not my vue component not re-rendering?

I have a question why not this component, not re-rendering after changing value so what I'm trying to do is a dynamic filter like amazon using the only checkboxes so let's see
I have 4 components [ App.vue, test-filter.vue, filtersInputs.vue, checkboxs.vue]
Here is code sandbox for my example please check the console you will see the value changing https://codesandbox.io/s/thirsty-varahamihira-nhgex?file=/src/test-filter/index.vue
the first component is App.vue;
<template>
<div id="app">
<h1>Filter</h1>
{{ test }}
<test-filter :filters="filters" :value="test"></test-filter>
</div>
</template>
<script>
import testFilter from "./test-filter";
import filters from "./filters";
export default {
name: "App",
components: {
testFilter,
},
data() {
return {
filters: filters,
test: {},
};
},
};
</script>
so App.vue that holds the filter component and the test value that I want to display and the filters data is dummy data that hold array of objects.
in my test-filter component, I loop throw the filters props and the filterInputs component output the input I want in this case the checkboxes.
test-filter.vue
<template>
<div class="test-filter">
<div
class="test-filter__filter-holder"
v-for="filter in filters"
:key="filter.id"
>
<p class="test-filter__title">
{{ filter.title }}
</p>
<filter-inputs
:value="value"
:filterType="filter.filter_type"
:options="filter.options"
#checkboxChanged="checkboxChanged"
></filter-inputs>
</div>
</div>
<template>
<script>
import filterInputs from "./filterInputs";
export default {
name: "test-filter",
components: {
filterInputs,
},
props:{
filters: {
type: Array,
default: () => [],
},
value: {
type: Array,
default: () => ({}),
},
},
methods:{
checkboxChanged(value){
// Check if there is a array in checkbox key if not asssign an new array.
if (!this.value.checkbox) {
this.value.checkbox = [];
}
this.value.checkbox.push(value)
}
};
</script>
so I need to understand why changing the props value also change to the parent component and in this case the App.vue and I tried to emit the value to the App.vue also the component didn't re-render but if I check the vue dev tool I see the value changed but not in the DOM in {{ test }}.
so I will not be boring you with more code the filterInputs.vue holds child component called checkboxes and from that, I emit the value of selected checkbox from the checkboxes.vue to the filterInputs.vue to the test-filter.vue and every component has the value as props and that it if you want to take a look the rest of components I will be glad if you Did.
filterInpust.vue
<template>
<div>
<check-box
v-if="filterType == checkboxName"
:options="options"
:value="value"
#checkboxChanged="checkboxChanged"
></check-box>
</div>
</template>
<script>
export default {
props: {
value: {
type: Object,
default: () => ({}),
},
options: {
type: Array,
default: () => [],
},
methods: {
checkboxChanged(value) {
this.$emit("checkboxChanged", value);
},
},
}
</script>
checkboxes.vue
<template>
<div>
<div
v-for="checkbox in options"
:key="checkbox.id"
>
<input
type="checkbox"
:id="`id_${_uid}${checkbox.id}`"
#change="checkboxChange"
:value="checkbox"
/>
<label
:for="`id_${_uid}${checkbox.id}`"
>
{{ checkbox.title }}
</label>
</div>
</div>
<template>
<script>
export default {
props: {
value: {
type: Object,
default: () => ({}),
},
options: {
type: Array,
default: () => [],
},
}
methods: {
checkboxChange(event) {
this.$emit("checkboxChanged", event.target.value);
},
},
};
</script>

I found the solution As I said in the comments the problem was that I'm not using v-model in my checkbox input Vue is a really great framework the problem wasn't in the depth, I test the v-model in my checkbox input and I found it re-render the component after I select any checkbox so I search more and found this article and inside of it explained how we can implement v-model in the custom component so that was the solution to my problem and also I update my codeSandbox Example if you want to check it out.
Big Thaks to all who supported me to found the solution: sarkiroka, Jakub A Suplick

Combine vue props with v-for

Here's sample of my child component
HTML:
<div v-for="(input, index) in form.inputs" :key="index">
<div>
<input :name"input.name" :type="input.type" />
</div>
</div>
JavaScript (Vue):
<script>
export default {
name: "child",
props: ['parentForm'],
data() {
return {
form: {
inputs: [
{
name: 'name',
type: 'text'
],
[...]
}
}
}
And sample of root component
HTML:
<child :parentsForm="form"></child>
JavaScript (Vue):
<script>
import child from "./child";
export default {
name: "root",
components: { child },
data() {
return {
form: {
data: {
name: null,
email: null,
...
}
}
}
The question is, how do I achieve combining root + v-for?
Example I want to using child component this way
<input :name"input.name" :type="input.type" v-model="parentForm.data . input.name" />
Since parentForm.data will bind form:data:{ and this will be the variable get from input.name }
Output in v-model should be bind form.data.name or form.data.email on root component
Thank you

You can use it as per follow,
<input :name="input.name" :type="input.type" v-model="parentForm.data[input.name]" />
This will bind parentForm.data.name for input.name = 'name' to v-model.

If I understood you correctly, you want to update parent data from your child component. If yes then you have two options.
In you child component use $parent.form.data to bind.
Or you can pass it down as prop assign it to a data property in child. Bind this new data property in your child and emit it whenever any changes are made. Receive this emit in your parent and update the parent property respectively (Recommended)