How to build a recursive component into a tree menu in Vue.js

This time I will show you how Vue.js builds recursive components into tree menus. What are the precautions for Vue.js to build recursive components into tree menus? The following are Let’s take a look at practical cases.

In Vue.js, a recursive component calls itself, such as:

Vue.component('recursive-component', {
 template: `<!--Invoking myself!-->
    <recursive-component></recursive-component>
 });

Recursive components are often used to display comments on blogs, nested menus, or basically the same type as parent and child, although the specific content is different.

Now to show you how to use recursive components effectively, I will proceed step by step by building an expandable/collapse tree menu.

data structure

A recursive component of a tree UI would be a visual representation of some recursive data structure. In this tutorial we will use a tree structure where each node is an object:

A label attribute.

If it has child nodes, a nodes property is an array property of one or more nodes.

Like all tree structures, it must have a root node, but can be infinitely deep.

let tree = {
 label: 'root',
 nodes: [
  {
  label: 'item1',
  nodes: [
   {
   label: 'item1.1'
   },
   {
   label: 'item1.2',
   nodes: [
    {
    label: 'item1.2.1'
    }
   ]
   }
  ]
  }, 
  {
  label: 'item2' 
  }
 ]
 }

Recursive components

Let's make a recursive component to display our data structure called TreeMenu. It only displays the current node's label, and calls itself to display any child nodes. File name: TreeMenu.vue, content is as follows:

<template>
 <p class="tree-menu">
  <p>{{ label }}</p>
  <tree-menu 
  v-for="node in nodes" 
  :nodes="node.nodes"
  :label="node.label"
  >
  </tree-menu>
 </p>
 </template>
 <script>
 export default { 
  props: [ 'label', 'nodes' ],
  name: 'tree-menu'
 }
 </script>

If you use a component recursively, you must first give Vue.component a global definition, or give it a name attribute. Otherwise, any child component will not be able to call it further and you will get an undefined "undefined component error" error message.

Basic events

As with any recursive function, you need a base event to end the recursion, otherwise rendering will continue indefinitely, eventually causing a stack overflow.

In the tree menu, we want to stop the recursion when we reach a node that has no children. You can do this with v-if, but we choose to use v-for This will be implemented for us implicitly; if the nodes array doesn't have any further definition the tree-menu component will be called. The template.vue file is as follows:

<template>
 <p class="tree-menu">
  ...
  <!--If `nodes` is undefined this will not render-->
  <tree-menu v-for="node in nodes"></tree-menu>
 </template>

Usage

How do we use this component now? First, we declare a Vue instance with a data structure including the data attribute and the defined treemenu component. The app.js file is as follows:

 import TreeMenu from './TreeMenu.vue'
 let tree = {
 ...
 }
 new Vue({
 el: '#app',
 data: {
  tree
 },
 components: {
  TreeMenu
 }
 })

Remember, our data structure has a root node. We start calling the TreeMenu component recursively from the main template, using the root nodes attribute to props:

<p id="app">
 <tree-menu :label="tree.label" :nodes="tree.nodes"></tree-menu>
 </p>

It's good to visually identify the "depth" of subcomponents so users can get a feel for the data structure from the UI. Let's achieve this by indenting the child nodes at each level.

This is achieved by adding a depth prop definition through TreeMenu. We will use this value to dynamically bind inline styles with transforms: we will use the transform: translate CSS rule for each node's label, thus creating an indent. template.vue is modified as follows**:**

<template>
 <p class="tree-menu">
  <p :style="indent">{{ label }}</p>
  <tree-menu 
  v-for="node in nodes" 
  :nodes="node.nodes" 
  :label="node.label"
  :depth="depth + 1"
  >
  </tree-menu>
 </p>
 </template>
 <script>
 export default { 
  props: [ 'label', 'nodes', 'depth' ],
  name: 'tree-menu',
  computed: {
  indent() {
   return { transform: `translate(${this.depth * 50}px)` }
  }
  }
 }
 </script>

The depth attribute starts from zero in the main template. In the component template above, you can see that this value is incremented every time it is passed to any child node.

<p id="app">
 <tree-menu 
  :label="tree.label" 
  :nodes="tree.nodes"
  :depth="0"
 ></tree-menu>
 </p>

Note: Remember to v-bind the depth value to ensure it is a JavaScript number type and not a string.

Expand/Collapse

Because recursive data structures can be large, a good UI trick for displaying them is to hide all nodes except the root node so that the user can expand or collapse the nodes as needed.

To do this, we will add a local property showChildren. If its value is False, the child node will not be rendered. This value should be toggled by clicking on the node, so we need to use a click event listener method toggleChildren to manage it. The template.vue file is modified as follows**:**

<template>
 <p class="tree-menu">
  <p :style="indent" @click="toggleChildren">{{ label }}</p>
  <tree-menu 
  v-if="showChildren"
  v-for="node in nodes" 
  :nodes="node.nodes" 
  :label="node.label"
  :depth="depth + 1"
  >
  </tree-menu>
 </p>
 </template>
 <script>
 export default { 
  props: [ 'label', 'nodes', 'depth' ],
  data() {
  return { showChildren: false }
  },
  name: 'tree-menu',
  computed: {
  indent() {
   return { transform: `translate(${this.depth * 50}px)` }
  }
  },
  methods: {
  toggleChildren() {
   this.showChildren = !this.showChildren;
  }
  }
 }
 </script>

Summarize

This way, we have a working tree menu. As a finishing touch, you can add a plus/minus icon to make the UI more visible. I also added very good fonts and computing performance based on the original showChildren

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!

Recommended reading:

How to use JSONAPI in PHP

How to use VueRouter’s navigation guard

The above is the detailed content of How to build a recursive component into a tree menu in Vue.js. For more information, please follow other related articles on the PHP Chinese website!