小程序实现短信登录倒计时

在平时的短信登录中，当发送短信验证码后会显示倒计时，那么这个倒计时如何实现呢？

wxml文件

<view class='Form'>
 <form bindsubmit="formSubmit" bindreset="formReset" class='forms'>
 <view class="fidpas">
 <input type="number" class="phonenumber" placeholder="请输入手机号" name="phonenumber" />
 <input type="number" class="message" placeholder="请输入短信验证码" name="msg" />
 <button class="{{sendmsg}}" bindtap="sendmessg" class='btn'>{{getmsg}}</button>
 </view>
 <button class="lgbut" formType="submit" type='warn'>下一步</button>
 </form>
</view>

js文件

let timeId = null;
Page({
 data: {
 sendmsg: "sendmsg",
 getmsg: "获取短信验证码",
 },
 sendmessg: function (e) {
 var timer=1;
 if (timer == 1) {
 timer = 0
 var that = this
 var time = 60
 that.setData({
 sendmsg: "sendmsgafter",
 })
 var inter = setInterval(function () {
 that.setData({
 getmsg: time + "s后重新发送",
 })
 time --
 if (time < 0) {
 timer = 1
 clearInterval(inter)
 that.setData({
 sendmsg: "sendmsg",
 getmsg: "获取短信验证码",
 })
 }
 }, 1000)
 }
 }, 
 })

wxss文件

.Form{
 margin-top: 80px;
}
.forms input{
 padding: 10px ;
}
.phonenumber{
 border-bottom: 1px solid #ccc;}
.message{
 display: inline-block
}
.btn{
 display: inline-block;
 font-size: 14px;
}
.forms button{
 margin-top: 15px;
}

效果图