1.wxml

<button class="btn_yzm" catchtap="getYzm" disabled="{{yzmDisabled}}"><text>{{yzm}}</text></button>

2.wxss
实现button内多行文字垂直居中

.btn_yzm {
  font-size: 24rpx;
  color: #EB602E;
  border: 2rpx solid #EB602E;
  background-color: #fff;
  border-radius: 20rpx;
  padding: 0px;
  height:80rpx;
  width: 100%;
  line-height: 30rpx;//缩小行间距

  display: table;
}
.btn_yzm text {
  vertical-align:middle;
  display: table-cell;
}

3.js
实现短信倒计时

Page({

  /**
   * 需要指定换行的地方\n(不加不影响垂直居中)
   */
  data: {
    yzm: '获取短信\n验证码',
    yzmDisabled: false,
  },
  getYzm: function () {
    var self = this;
    self.changeYzm();

  },
  changeYzm: function () {
    var self = this;
    var n = 10;
    self.setData({
      //禁用button
      yzmDisabled: true,
      yzm: n,
    })

    var yzmInterval = setInterval(function () {
      if (self.data.yzm <= 0) {
        self.setData({
          yzm: '获取短信\n验证码',
          yzmDisabled: false,
        })
        clearInterval(yzmInterval);
      } else {
        n = n - 1;
        self.setData({
          yzm: n,
        }) 
      }
    }, 1000)
  }