Updating parent data via child component?

Question

What is correct procedure to update parent data via child component?

In the child component - I am modifying parent data directly via props. I am not sure if this is wrong way to go about it.

According to the vue doc:

when the parent property updates, it will flow down to the child, but not the other way around.

Example child component :

<script>
    export default {

        props: ['user'],

        data: function () {
            return {
                linkName: '',
                linkValue: '',
            }
        },

        methods: {
            addLink: function (event) {
                event.preventDefault();
                this.$http.post('/user/link', {name: this.linkName, key: this.linkValue}).then(response => {
                    this.user.links.push(response.data);
                }, response => {
                      // Error
                    }
                });
            },
        }
    }
</script>

I have used this.user.links.push(response.data); which modify the data directly to the parent component via props: ['user']

Answer 1

As you rightly said, the props is not meant to pass data from child to parent. The data binding is one-way only.

The correct procedure is for child component to send an event via $emit to the parent component, along with some value (optional).

In your case, you may do the following in the addLink method of child component:

this.$http.post('/user/link', {name: this.linkName, key: this.linkValue}).then(response => {
    this.$emit("update-user-links", response.data);  // Send an event to parent, with data
}, response => {
    // Error
});

And your parent can listen to it as follows:

<my-user-link-component :user="userData" v-on:update-user-links="addUserLink"></my-user-link-component>

or the short-hand syntax:

<my-user-link-component :user="userData" @update-user-links="addUserLink"></my-user-link-component>

In the above, you are assigning a method addUserLink to handle the child component's event. In your parent component, you need to define this method as follows:

methods: {
    // ... your other methods,
    addUserLink: function(linkData) {
        this.userData.links.push(linkData);
    }
}

Benefits of this one-way binding from top to bottom and the event mechanism:

• Your parent component can choose to ignore events if it wants - thus making child components reusable in other contexts.
• Your child components (assuming you have many) will be allowed to send only events upwards, which is easier to debug when compared to each of them directly mutating parent state.