SOURCE

 
//倒计时  
var countdown=60;  
function settime(val) {  
    if (countdown == 0) {  
        val.removeAttribute("disabled");  
        val.value="获取验证码";  
        countdown = 60;  
        return false;  
    } else {  
        val.setAttribute("disabled", true);  
        val.value="重新发送(" + countdown + ")";  
        countdown--;  
    }  
    setTimeout(function() {  
        settime(val);  
    },1000);  
}  

<div class="div user-input">  
  <input type="number" class="code" placeholder="请输入手机验证码" required maxlength="6">  
  <input type="button" class="obtain generate_code" value=" 获取验证码" onclick="settime(this);">  
</div>