<style>
button{
  background: #45BCF9;
  color: #fff;
  padding: 4px 10px;
  border: none;
  outline: none;
  cursor: pointer;
}
button:hover{
  background: #00a8fe;
}
button.disabled{
  background: #000;
  cursor: auto;
}
button.disabled:hover{
  background: #000;
}
</style>
<button type="button" onclick="fn()">获取验证码</button>
<script>
function fn(){
  var oBtn = document.getElementsByTagName('button')[0];
  var time = 60;
  var timer = null;
  oBtn.innerHTML = time + '秒后重新发送';
  oBtn.setAttribute('disabled', 'disabled');  // 禁用按钮
  oBtn.setAttribute('class', 'disabled');   // 添加class 按钮样式变灰
  timer = setInterval(function(){
    // 定时器到底了 兄弟们回家啦
    if(time == 1){
      clearInterval(timer);       
      oBtn.innerHTML = '获取验证码';  
      oBtn.removeAttribute('disabled'); 
      oBtn.removeAttribute('class');  
    }else{
      time--;
      oBtn.innerHTML = time + '秒后重新发送';
    }
  }, 1000)
}
</script>