JavaScript实现京东快递单号实时预览效果

<style>
  * {
  padding: 0;
  margin: 0;
  }
  .search {
  position: relative;
  width: 178px;
  margin: 100px;
  }
  .con {
  display: none;
  position: absolute;
  top: -48px;
  width: 171px;
  border: 1px solid rgba(0, 0, 0, 0.2);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
  padding: 5px 0;
  font-size: 18px;
  line-height: 20px;
  color: #333;
  }
  .con::before {
  content: "";
  width: 0;
  height: 0;
  position: absolute;
  top: 28px;
  left: 18px;
  border: 8px solid #000;
  border-style: solid dashed dashed;
  border-color: #fff transparent transparent;
  }
 </style>
 </head>
 <body>
 <div class="search">
  <div class="con"></div>
  <input type="text" placeholder="请输入您的快递单号" class="jd" />
 </div>
 <script>
  var con = document.querySelector(".con");
  var jd_input = document.querySelector(".jd");
  jd_input.addEventListener("keyup", function () {
  if (this.value == "") {
   con.style.display = "none";
  } else {
   con.style.display = "block";
   con.innerHTML = this.value;
  }
  });
  //当失去焦点，就隐藏盒子
  jd_input.addEventListener("blur", function () {
  con.style.display = "none";
  });
  //当获得焦点，就显示盒子
  jd_input.addEventListener("focus", function () {
  if (this.value !== "") {
   con.style.display = "block";
  }
  });
 </script>
</body>