Tips and best practices for using directives to implement table trees in Vue

With the increasing development of the Internet, front-end frameworks are becoming more and more mature and perfect. Vue.js is one of the best. Its component development model and responsive features make front-end development faster, easier, and more efficient. Efficient. Among them, Directive is a very important concept and function in Vue.js, which facilitates users to extend the behavior and DOM operations of Vue.js to achieve richer and more flexible functions. This article will introduce tips and best practices for implementing table trees in Vue.js using Directives.

1. Overview of Directive

Directive (instruction) is a special tag in Vue.js. It is different from the traditional HTML tag. Its function is to operate the DOM and has a strong With its functions and flexibility, you can write and use it according to your own needs.

Take the v-if instruction that comes with Vue.js as an example. When the result of the specified expression is true, the corresponding node will be created/updated on the DOM tree according to the element tag where the instruction is located; when the specified When the value of the expression is false, the corresponding node will be removed from the DOM tree. This is the basic way to use Directive.

2. Implementation of table tree

Table tree is data displayed in a tree structure in a table. It is a common way of displaying data. In the process of implementing the table tree, we can use the instructions in Vue.js to achieve it.

In Directive, there are two important concepts, one is hook function (Hook Function) and the other is dom element operation (DOM Operation).

The hook function is represented by the life cycle function. For the implementation of most DOM operations, it mainly includes the five functions bind, inserted, update, componentUpdated and unbind. Among them, the bind function will be executed when the instruction is bound to the element, the inserted function will be executed when the element is inserted into the parent node, the update function will be executed when the element is updated, the componentUpdated function will be executed after the component is updated, and the unbind function will Executed when the command is unbound.

DOM element operation means that in instructions, we can directly operate DOM elements to achieve the functions we want. Including operations such as createElement, appendChild, removeChild, classList.add, etc.

Next, we will analyze in detail the specific implementation steps of implementing table trees in Vue.js based on Directive's hook functions and DOM element operations.

(1) Data preparation

First, we need to prepare a set of data to store all the data of the table tree, and operate and update it in subsequent operations.

const data = [{
    id: 1,
    name: 'Parent 1',
    children: [{
      id: 2,
      name: 'Child 1 of Parent 1'
    }, {
      id: 3,
      name: 'Child 2 of Parent 1',
      children: [{
        id: 4,
        name: 'Child 1 of Child 2 of Parent 1'
      }]
    }]
  },
  {
    id: 5,
    name: 'Parent 2'
  }
]

(2) Definition of directive

Next, we need to define a Directive named table-tree, and according to the life cycle function of the directive, in different Perform specific DOM operations in the link.

<template>
  <div>
    <table>
      <thead>
        <tr>
          <th>ID</th>
          <th>Name</th>
        </tr>
      </thead>
      <tbody>
        <tr 
          v-for="node in treeData" 
          v-table-tree:node="{node: node, level: 0}" 
          :class="{'tree-row': node.hasChildren}" 
          :key="node.id">
          <td>{{node.id}}</td>
          <td>{{node.name}}</td>
        </tr>
      </tbody>
    </table>
  </div>
</template>

<script>
export default {
  directives: {
    'table-tree': {
      bind: function (el, binding) {
        const table = el.querySelector('table') // 获取 table 元素
        const {node} = binding.value
        const childNodes = node.children
        if (childNodes && childNodes.length) {
          const parentTr = el.querySelector(`[key="${node.id}"]`) // 获取当前节点对应的 tr 元素
          const trLength = parentTr.querySelectorAll('td').length // 获取 tr 中子 td 的数量
          const td = document.createElement('td')
          td.setAttribute('colspan', trLength)
          td.innerHTML = '<div class="tree-content"></div>'
          parentTr.appendChild(td) // 增加一个 td 元素，用于放置下一级节点
          const childTable = document.createElement('table') // 新增一个 table 元素，用于放置下一级节点的数据
          td.querySelector('.tree-content').appendChild(childTable)

          childNodes.forEach((child) => { // 递归处理下一级节点
            child.hasChildren = !!child.children
            const tr = document.createElement('tr')
            tr.setAttribute('key', child.id)
            tr.classList.add('tree-child-row')
            childTable.appendChild(tr)
            const td = document.createElement('td')
            td.innerHTML = child.name
            td.classList.add('tree-child-content')
            tr.appendChild(td)
            if (child.children) {
              const innerTd = document.createElement('td')
              tr.appendChild(innerTd)
              const innerTable = document.createElement('table')
              innerTable.setAttribute('class', 'tree-inner-table')
              innerTd.appendChild(innerTable)
              this.$options.directives['table-tree'].bind(innerTable, {value: {node: child, level: binding.value.level + 1}})
            }
          })
        }
      },
      unbind: function(el, binding) {
      }
    }
  },
  props: {
    treeData: {
      type: Array,
      required: true
    }
  }
}
</script>

<style>
.tree-row .tree-content:before {
  content: '';
  display: inline-block;
  width: 16px;
  height: 16px;
  margin-right: 5px;
  vertical-align: middle;
  background-image: url('expanding-arrow.png'); /* 展开箭头图标 */
  background-repeat: no-repeat;
  background-position: center center;
}
.tree-row:not(.expanded) .tree-content:before {
  transform: rotate(-90deg);
}
.tree-row.expanded .tree-content:before {
  transform: rotate(0);
}
.tree-child-row {
  display: none;
}
.tree-row.expanded ~ .tree-child-row {
  display: table-row;
}
</style>

(3) Effect display

Since then, we have completed all operations to implement the table tree. For specific effect display, please refer to the screenshot below.

三, Summary

This article mainly introduces the techniques and best practices for using directives to implement table trees in Vue.js. Through hook functions and DOM element operations, we can easily obtain and operate DOM elements to achieve the functions we expect. At the same time, the directive function of Vue.js also provides us with great flexibility and scalability, and can be customized according to personal needs.

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