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                <div id="app">
  <input type="text" @keydown="handleKeyDown">:输入的实时弹出内容
  <input type="text" @keydown.enter="handleKeyDown">:回车/enter 的时候弹出结果
  <input type="text" @keydown.delete="handleKeyDown">:delete的时候弹出结果
  <input type="text" @keydown.esc="handleKeyDown">:esc的时候弹出结果
  <input type="text" @keydown.shift="handleKeyDown">:shift的时候弹出结果
  <input type="text" @keydown.alt="handleKeyDown">:alt的时候弹出结果
  <input type="text""handleKeyDown">:tab的时候弹出结果




                var app = new Vue({
  el: "#app",
  methods: {
    handleKeyDown: function (e) {
      // 指的是 input dom框这个节点,通过原生value可以把输入框的内容弹出来