JavaScript实现短信验证码5秒倒计时功能详解

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>js-手机发送短信倒计时</title>
 <style>
  button{
   width: 100px;
   height: 30px;
   border: none;
  }
  input{
   outline: none;
  }
 </style>
 <script> 
  window.onload = function(){
   function $(id){ return document.getElementById(id); } 
   $('btn').onclick = function(){
    clearInterval(timer); //清除计时器 
    var that = this;
    that.disabled = true;
    var count = 5;
    var timer = setInterval(function(){
     if(count>0){
      count--;
      that.innerHTML = "剩余时间"+ count +"s";
     }else{
      that.innerHTML ="重新发送短信";
      that.disabled = false;
      clearInterval(timer); //清除计时器
     }
    },1000);
   }
  }
 </script>
</head>
<body>
 <div class="box">
  <input type="text" id="txt">
  <button id="btn" >点击发送短信</button>
 </div>
</body>
</html> 

<script> 
  window.onload = function(){
   function $(id){ return document.getElementById(id); } 
   $('btn').onclick = function(){
    var that = this;
    that.disabled = true;
    var count = 5;
    var timer = setTimeout(fn,1000);
    function fn(){
     count--;
     if(count>0){
      that.innerHTML = "剩余时间"+ count +"s";
      setTimeout(fn,1000); 
     }else{
      that.innerHTML ="重新发送短信";
      that.disabled = false; 
     }
    }
   }
  }
 </script>