vuejs update parent data from child component

I'm starting to play with vuejs (2.0). I built a simple page with one component in it. The page has one Vue instance with data. On that page I registered and added the component to html. The component has one input[type=text]. I want that value to reflect on the parent (main Vue instance).

How do I correctly update the component's parent data? Passing a bound prop from the parent is not good and throws some warnings to the console. They have something in their doc but it is not working.

Two-way binding has been deprecated in Vue 2.0 in favor of using a more event-driven architecture. In general, a child should not mutate its props. Rather, it should $emit events and let the parent respond to those events.

In your specific case, you could use a custom component with v-model. This is a special syntax which allows for something close to two-way binding, but is actually a shorthand for the event-driven architecture described above. You can read about it here -> https://vuejs.org/v2/guide/components.html#Form-Input-Components-using-Custom-Events.

Here's a simple example:

Vue.component('child', {
  template: '#child',
  
  //The child has a prop named 'value'. v-model will automatically bind to this prop
  props: ['value'],
  methods: {
    updateValue: function (value) {
      this.$emit('input', value);
    }
  }
});

new Vue({
  el: '#app',
  data: {
    parentValue: 'hello'
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.13/vue.js"></script>

<div id="app">
  <p>Parent value: {{parentValue}}</p>
  <child v-model="parentValue"></child>
</div>

<template id="child">
   <input type="text" v-bind:value="value" v-on:input="updateValue($event.target.value)">
</template>

---

The docs state that

<custom-input v-bind:value="something" v-on:input="something = arguments[0]"></custom-input>

is equivalent to

<custom-input v-model="something"></custom-input>

That is why the prop on the child needs to be named value, and why the child needs to $emit an event named input.

In child component:

this.$emit('eventname', this.variable)

In parent component:

<component @eventname="updateparent"></component>

methods: {
    updateparent(variable) {
        this.parentvariable = variable
    }
}

From the documentation:

>In Vue.js, the parent-child component relationship can be summarized as props down, events up. The parent passes data down to the child via props, and the child sends messages to the parent via events. Let’s see how they work next.

How to pass props

Following is the code to pass props to a child element:

<div>
  <input v-model="parentMsg">
  <br>
  <child v-bind:my-message="parentMsg"></child>
</div>

How to emit event

HTML:

<div id="counter-event-example">
  <p>{{ total }}</p>
  <button-counter v-on:increment="incrementTotal"></button-counter>
  <button-counter v-on:increment="incrementTotal"></button-counter>
</div>

JS:

Vue.component('button-counter', {
  template: '<button v-on:click="increment">{{ counter }}</button>',
  data: function () {
    return {
      counter: 0
    }
  },
  methods: {
    increment: function () {
      this.counter += 1
      this.$emit('increment')
    }
  },
})
new Vue({
  el: '#counter-event-example',
  data: {
    total: 0
  },
  methods: {
    incrementTotal: function () {
      this.total += 1
    }
  }
})

Child Component

Use this.$emit('event_name') to send an event to the parent component.

Parent Component

In order to listen to that event in the parent component, we do v-on:event_name and a method (ex. handleChange) that we want to execute on that event occurs

Done :)

I agree with the event emitting and v-model answers for those above. However, I thought I would post what I found about components with multiple form elements that want to emit back to their parent since this seems one of the first articles returned by google.

I know the question specifies a single input, but this seemed the closest match and might save people some time with similar vue components. Also, no one has mentioned the .sync modifier yet.

As far as I know, the v-model solution is only suited to one input returning to their parent. I took a bit of time looking for it but Vue (2.3.0) documentation does show how to sync multiple props sent into the component back to the parent (via emit of course).

It is appropriately called the .sync modifier.

Here is what the documentation says:

> In some cases, we may need “two-way binding” for a prop. > Unfortunately, true two-way binding can create maintenance issues, > because child components can mutate the parent without the source of > that mutation being obvious in both the parent and the child. > > That’s why instead, we recommend emitting events in the pattern of > update:myPropName. For example, in a hypothetical component with a > title prop, we could communicate the intent of assigning a new value > with:

this.$emit('update:title', newTitle)

> Then the parent can listen to > that event and update a local data property, if it wants to. For > example:

<text-document   
 v-bind:title="doc.title"  
 v-on:update:title="doc.title = $event"
></text-document>

> For convenience, we offer a shorthand for this pattern with the .sync modifier:

<text-document v-bind:title.sync="doc.title"></text-document>

You can also sync multiple at a time by sending through an object. Check out the documentation here

The way more simple is use this.$emit

Father.vue

<template>
  <div>
    <h1>{{ message }}</h1>
    <child v-on:listenerChild="listenerChild"/>
  </div>
</template>

<script>
import Child from "./Child";
export default {
  name: "Father",
  data() {
    return {
      message: "Where are you, my Child?"
    };
  },
  components: {
    Child
  },
  methods: {
    listenerChild(reply) {
      this.message = reply;
    }
  }
};
</script>

Child.vue

<template>
  <div>
    <button @click="replyDaddy">Reply Daddy</button>
  </div>
</template>

<script>
export default {
  name: "Child",
  methods: {
    replyDaddy() {
      this.$emit("listenerChild", "I'm here my Daddy!");
    }
  }
};
</script>

My full example: https://codesandbox.io/s/update-parent-property-ufj4b

It is also possible to pass props as Object or Array. In this case data will be two-way binded:

(This is noted at the end of topic: https://vuejs.org/v2/guide/components.html#One-Way-Data-Flow )

Vue.component('child', {
  template: '#child',
  props: {post: Object},
  methods: {
    updateValue: function () {
      this.$emit('changed');
    }
  }
});

new Vue({
  el: '#app',
  data: {
    post: {msg: 'hello'},
    changed: false
  },
  methods: {
    saveChanges() {
        this.changed = true;
    }
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.13/vue.js"></script>

<div id="app">
  <p>Parent value: {{post.msg}}</p>
  <p v-if="changed == true">Parent msg: Data been changed - received signal from child!</p>
  <child :post="post" v-on:changed="saveChanges"></child>
</div>

<template id="child">
   <input type="text" v-model="post.msg" v-on:input="updateValue()">
</template>

In Parent Conponent -->

> data : function(){ > return { > siteEntered : false, > }; > },

In Child Component -->

> this.$parent.$data.siteEntered = true;

2021 ANSWER - Vue 2.3+

SHORT ANSWER: Just add .sync modifier in the parent and pass the data as props to the children:

    // PARENT:
    data () {
    return {
      formData: {
        members: [] //<- we wanna pass this one down to children and add/remove from the child component
      }
    }

   // PARENT TEMPLATE:
   <!-- ADD MEMBERS -->
  <add-members :members.sync="formData.members" />

Nested child component: AddMembers.vue

export default {
  name: 'AddMembers',
  props: ['members'],
  methods: {
    addMember () {
      this.members.push(new Member()) // <-- you can play and reactivity will work (in the parent)  
    },
    removeMember (index) {
      console.log('remove', index, this.members.length < 1)
      this.members.splice(index, 1)
    }
  }
}

Long story: changes from the child component in reallity are being $emitted and updating formData.members[] of the parent.

source: Mauro Perez at medium

In the child

 <input
            type="number"
            class="form-control"
            id="phoneNumber"
            placeholder
            v-model="contact_number"
            v-on:input="(event) => this.$emit('phoneNumber', event.target.value)"
    />

data(){
    return {
      contact_number : this.contact_number_props
    }
  },
  props : ['contact_number_props']

In parent

<contact-component v-on:phoneNumber="eventPhoneNumber" :contact_number_props="contact_number"></contact-component>


 methods : {
     eventPhoneNumber (value) {
      this.contact_number = value
    }

The correct way is to $emit() an event in the child component that the main Vue instance listens for.

// Child.js
Vue.component('child', {
  methods: {
    notifyParent: function() {
      this.$emit('my-event', 42);
    }
  }
});

// Parent.js
Vue.component('parent', {
  template: '<child v-on:my-event="onEvent($event)"></child>',
  methods: {
    onEvent: function(ev) {
      v; // 42
    }
  }
});

Another way is to pass a reference of your setter from the parent as a prop to the child component, similar to how they do it in React. Say, you have a method updateValue on the parent to update the value, you could instantiate the child component like so: <child :updateValue="updateValue"></child>. Then on the child you will have a corresponding prop: props: {updateValue: Function}, and in the template call the method when the input changes: <input @input="updateValue($event.target.value)">.

I don't know why, but I just successfully updated parent data with using data as object, :set & computed

Parent.vue

<!-- check inventory status - component -->
    <CheckInventory :inventory="inventory"></CheckInventory>

data() {
            return {
                inventory: {
                    status: null
                },
            }
        },

Child.vue

<div :set="checkInventory">

props: ['inventory'],

computed: {
            checkInventory() {
                
                this.inventory.status = "Out of stock";
                return this.inventory.status;

            },
        }

his example will tell you how to pass input value to parent on submit button.

First define eventBus as new Vue.

//main.js
import Vue from 'vue';
export const eventBus = new Vue();

Pass your input value via Emit.
//Sender Page
import { eventBus } from "../main";
methods: {
//passing data via eventbus
    resetSegmentbtn: function(InputValue) {
        eventBus.$emit("resetAllSegment", InputValue);
    }
}

//Receiver Page
import { eventBus } from "../main";

created() {
     eventBus.$on("resetAllSegment", data => {
         console.log(data);//fetching data
    });
}

I think this will do the trick:

@change="$emit(variable)"

Intro

I was looking for sending data from parent to child (and back) in vue3 (I know the question was about vue2, but there are no references for vue3 on SO at the time).

Below is the working boilerplate result, pure "html + js", no packagers, modules, etc with few caveats I had, explained.

Notes:

1. Tnserting the child - line > html > <component-a :foo="bar" @newfooevent="bar = $event"></component-a>` >

• I bind parent.bar to child.foo using short-hand :foo="bar", same as v-bind:foo="bar". It passes data from parent to child through props.

• Caveat: Event listener should be placed in the child component tag only!

  That is the @newfooevent="bar = $event" part.

  You cannot catch the signal in the <div id="app"> or anywhere else inside the parent.

  Still, this is the parent's side of the universe, and here you can access all parent's data and extract the data from the child's signal to deal with it.

2. You can create app, and define component after it (the app.component("component-a", ...) part.

   Caveat: there are no need in forward declaration of components, e.g. functions in C/C++. You can create app which uses the component, and define the component afterwards. I lost a lot of time looking for the way to declare it somehow - no need.

3. Here you can find a nice example of the v-model usage, and the code I used to sort things out: https://javascript.plainenglish.io/vue-3-custom-events-d2f310fe34c9

The example

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>App</title>
    <meta charset="utf-8" />
    <script src="https://unpkg.com/vue@next"></script>
  </head>
  <body>
    <div id="app">
      <component-a :foo="bar" @newfooevent="bar = $event"></component-a>
      <p>Parent copy of `bar`: {{ bar }}</p>
      <button @click="bar=''">Clear</button>
    </div>

    <script>
      const app = Vue.createApp({
        data() {
          return {
            bar: "bar start value"
          };
        }
      });      

      app.component("component-a", {
        props: {
          foo: String
        },
        template: `
          <input 
            type="text"
            :value="foo"
            @input="$emit('newfooevent', $event.target.value)">
        `
      });      

      app.mount("#app");
    </script>
  </body>
</html>

There is another way of communicating data change from child to parent which uses provide-inject method. Parent component "provides" data or method for the child component, and this data or method is then "injected" into child component - but it can also be used for triggering a method in parent and passing it a parameter.
This approach can be especially useful when having a child component which happens to be embedded in multiple other components. Also, in a large project care must be taken not to lose overview of provide and inject usage.

Example of parent (top level) component App.vue using provide to give access to it's method updateParentValue (if method is provided and not data, provide is in form of a method):

<template>
  <h2>App.vue, parentValue is: <em>{{ parentValue }}</em></h2>
  <ChildComponent1 />
</template>

<script>
import ChildComponent1 from "./components/ChildComponent1.vue";

export default {
  data() {
    return {
      parentValue: "",
    };
  },
  components: {
    ChildComponent1,
  },
  provide() {
    return {
      updateParent: this.updateParentValue,
    };
  },
  methods: {
    updateParentValue($value) {
      this.parentValue = $value;
    },
  },
};
</script>

In this example component Component4.vue is in the "bottom", that is, App.vue contains Component1, Component1 contains Component2... until Component4 which actually utilizes inject to get access to parent method which is then invoked and a parameter $value is passed (just a random number here):

<template>
  <div>
    <h2>ChildComponent4.vue</h2>
    <button @click="updateParent(Math.random())">
      Update parent value in App.vue
    </button>
  </div>
</template>

<script>
export default {
  inject: ["updateParent"],
};
</script>

Entire example is available here.
Vue.js documentation