Tips for preventing directly mutating a prop within a recursive component

The child operates on its own copy of the prop data and can notify the parent using `$emit` when a change occurs.

Imagine dealing with a recursive tree structure, like a file system for example:

[
 { type: 'dir', name: 'music', children: [
    { type: 'dir', name: 'genres', children: [
       { type: 'dir', name: 'triphop', children: [
          { type: 'file', name: 'Portishead' },
          ...
       ]},
     ]}
   ]}
]}

A component called `Thing` is used recursively to handle a `childtree` prop as shown below:

<template>
  <input v-model="tree.name" />
  <thing v-for="childtree in tree.children" :tree="childtree" ></thing>
</template>

Modifying a name directly modifies the prop, triggering a warning from Vue.

To avoid direct prop modification, a deep copy of `childtree` would need to be made by each component. This copy would then be emitted via `$emit`, and upon receiving an input, it would copy the changes back to the original prop. This process would repeat throughout the tree, potentially causing inefficiency for larger trees.

Is there a more efficient solution to this problem? It's possible to workaround Vue warnings/errors using a trick demonstrated in this example jsfiddle.

Answer №1

If you're looking to solve the issue, consider passing only the event from the child component. Check out this solution on JSFiddle

<input @input="(e) => $emit('input', e.target.value)" />

Alternatively, I recommend using one of the following methods:

  1. Vuex,
  2. Event bus

This will improve code clarity and ensure a single source of truth.

Update: For cases of recursive inheritance, leveraging provide inject might be more convenient: JSFiddle Link for Recursive Inheritance

With provide inject, you can offer a function that can modify the state of the base component across all child components (the function needs to be injected).

Answer №2

The Importance of One-Way Data Flow in Vue

It is crucial to understand that in Vue, the flow of data is one-way from parent components to child components. Whenever the parent component updates, all props in the child component are automatically refreshed with the most recent values. Therefore, it is recommended not to try to change a prop's value within a child component as Vue will issue a warning in the console.

It should be noted that objects and arrays in JavaScript are passed by reference. Consequently, if the prop is an array or object, making changes directly to the object or array inside the child component will impact the state of the parent component.

An Illustration Using Lodash

Let's consider an example using the lodash library.

Initially, let's look at the clone method:

var objects = [{ 'a': 1 }, { 'b': 2 }];

var shallow = _.clone(objects);
console.log(shallow[0] === objects[0]); // => true

Next, we examine the cloneDeep method:

var objects = [{ 'a': 1 }, { 'b': 2 }];

var deep = _.cloneDeep(objects);
console.log(deep[0] === objects[0]); // => false

Hence, if you intend to modify a prop's value in a child component without affecting its parent, it is essential to utilize the cloneDeep function provided by lodash.

Answer №3

Here's how I've managed this scenario:

<template>
  <div>
    <input v-model="myName" @input="updateParent()" />
    <thing v-for="(child, i) in myChildren" :key="child.uniqueId"
     @input="setChild(i, $event)"
     >
    </thing>
  </div>
</template>
<script>
export default {
props: ['node'],
data() {
  return {
     myName: this.node.name,
     myChildren: this.node.children.slice(0),
  };
},
methods: {
  updateParent() {
    this.$emit('input', {name: this.myName, children: this.myChildren});
  },
  setchild(i, newChild) {
    this.$set(this.myChildren, i, newChild);
  }
}
}
</script>

For each node of the tree:

  • It operates on its own 'name' attribute.
  • It maintains its own collection of children (although the children are actual references belonging to an external object which should not be altered, but the array belongs to us).
  • It notifies the parent component to update itself when there is a change.
  • It listens for changes made to child nodes.

This method effectively avoids mutating props. One important aspect not shown here is assigning a unique ID to each child. I accomplished this by generating sequential IDs using a global counter (located on $root).

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