js获取快递单号小练习

1、css代码

2、html代码

3、js代码

完整代码

效果图

1、css代码

 .box{
            width: 400px;
            height: 300px;
            margin: 100px auto;
            position: relative;
        }
        input{
            width: 250px;
            height: 40px;
            outline: none;
        }
        span{
            display: block;
            position: absolute;
            min-width: 270px;
            max-width: 400px;
            /* width: 270px;
            height: 40px; */
           border: 1px solid red;
           top: -50px;
           word-wrap: break-word;
           margin-bottom: 20px;
           /* display: none; */
           opacity: 0;
           font-size: 18px;
           line-height: 20px;
        }

2、html代码

<div class="box">
        <span></span>
        <input type="text" placeholder="请输入您的快递单号">
    </div>

3、js代码

 <script>
        // 需求：获取焦点出现框，并内容实时与input同步
        const ipt=document.querySelector('input')
        const span=document.querySelector('span')
        //获取焦点，显示span
        ipt.addEventListener('focus',function() {
            
            // span.style.display='block'
       

          if(ipt.value.trim()===''){
            span.style.opacity=0
          }else{
            span.style.opacity=1
          }
            
         
        })
        //span的内容等于input框内容
        ipt.addEventListener('input',function() {
       
           
            if(ipt.value.trim() ===''){
                span.style.opacity=0
            }else{
                span.innerHTML=ipt.value
                span.style.opacity=1
            }
           
        })
        //失去焦点,隐藏span
        ipt.addEventListener('blur',function(){
            // span.style.display='none'
            span.style.opacity=0

        })
    </script>

完整代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 400px;
            height: 300px;
            margin: 100px auto;
            position: relative;
        }
        input{
            width: 250px;
            height: 40px;
            outline: none;
        }
        span{
            display: block;
            position: absolute;
            min-width: 270px;
            max-width: 400px;
            /* width: 270px;
            height: 40px; */
           border: 1px solid red;
           top: -50px;
           word-wrap: break-word;
           margin-bottom: 20px;
           /* display: none; */
           opacity: 0;
           font-size: 18px;
           line-height: 20px;
        }
    </style>
</head>
<body>
    <div class="box">
        <span></span>
        <input type="text" placeholder="请输入您的快递单号">
    </div>


    <script>
        // 需求：获取焦点出现框，并内容实时与input同步
        const ipt=document.querySelector('input')
        const span=document.querySelector('span')
        //获取焦点，显示span
        ipt.addEventListener('focus',function() {
            
            // span.style.display='block'
       

          if(ipt.value.trim()===''){
            span.style.opacity=0
          }else{
            span.style.opacity=1
          }
            
         
        })
        //span的内容等于input框内容
        ipt.addEventListener('input',function() {
       
           
            if(ipt.value.trim() ===''){
                span.style.opacity=0
            }else{
                span.innerHTML=ipt.value
                span.style.opacity=1
            }
           
        })
        //失去焦点,隐藏span
        ipt.addEventListener('blur',function(){
            // span.style.display='none'
            span.style.opacity=0

        })
    </script>
</body>
</html>