Custom command to get focus

// 对Vue的全局指令, 进行封装
// 封装中间件函数插件
const directiveObj = {
    
  install (Vue) {
    
    Vue.directive('focus', {
    
      // elRepresents the label where the command is located
      // 指令所在标签, is inserted into the realDOM时才触发, If the label is useddisplay:nonehide and reappear, 不会在触发inserted的
      inserted (el) {
    
        // 指令所在van-search组件
        // 组件根标签是div, input在内部
        // 以上都是原生标签对象
        // 搜索页面 el是div
        // 文章评论 el是textarea
        // 以后el还可能是input呢
        // 知识点: 原生DOM.nodeName Get the tag name (注意: 大写的字符串)
        if (el.nodeName === 'TEXTAREA' || el.nodeName === 'INPUT') {
    
          el.focus()
        } else {
    
          // elNot an input box by itself, Try to get it in there
          setTimeout(() => {
    
            const theInput = el.querySelector('input')
            const theTextArea = el.querySelector('textarea')
            // 判断: Not necessarily obtainable, 需要加判断, 有值了, 再执行.focus()才不报错
            if (theInput) theInput.focus()
            if (theTextArea) theTextArea.focus()
          })
        }
      },
      update (el) {
     // 指令所在标签, 被更新时触发
        if (el.nodeName === 'TEXTAREA' || el.nodeName === 'INPUT') {
    
          el.focus()
        } else {
    
          // elNot an input box by itself, Try to get it in there
          setTimeout(() => {
    
            const theInput = el.querySelector('input')
            const theTextArea = el.querySelector('textarea')
            // 判断: Not necessarily obtainable, 需要加判断, 有值了, 再执行.focus()才不报错
            if (theInput) theInput.focus()
            if (theTextArea) theTextArea.focus()
          })
        }
      }
    })
  }
}

export default directiveObj

在main.jsJust register globally
import directiveObj from ‘./utils/directive’
Vue.use(directiveObj)