<view class='top'>
 <text class="{{login?'active':''}}" catchtap='login'>登錄</text>
 <text class="{{login?'':'active'}}" catchtap='register'>注冊(cè)</text>
</view>
 
<view class='log' wx:if="{{login}}">
 <form>
 <input placeholder='賬號(hào)'/>
 <button>登錄</button>
 </form>
 
</view>
<view class='reg'wx:else>
 <form>
 <input placeholder='密碼'/>
 <button>注冊(cè)</button>
 </form>
</view>

.top{
 display: flex;
 flex-direction: row;
 height: 100rpx;
 border-bottom: 1px solid #ccc;
}
.top text{
 width: 50%;
 line-height: 100rpx;
 text-align: center;
}
.top .active{
 border-bottom: 2px solid red;
}
input{
 border-bottom: 1px solid #ccc;
 line-height: 100rpx;
 height: 100rpx;
 padding-left: 40rpx;
 margin-bottom: 40rpx;
}

Page({
 data: {
 login:true
 },
 
 /**
 * 生命周期函數(shù)--監(jiān)聽頁(yè)面加載
 */
 login:function(){
  this.setData({
  login:true
  });
 },
 register:function(){
 this.setData({
  login: false
 });
 },
 onLoad: function (options) {
 
 },
 
 /**
 * 生命周期函數(shù)--監(jiān)聽頁(yè)面初次渲染完成
 */
 onReady: function () {
 
 },
 
 /**
 * 生命周期函數(shù)--監(jiān)聽頁(yè)面顯示
 */
 onShow: function () {
 
 },
 
 /**
 * 生命周期函數(shù)--監(jiān)聽頁(yè)面隱藏
 */
 onHide: function () {
 
 },
 
 /**
 * 生命周期函數(shù)--監(jiān)聽頁(yè)面卸載
 */
 onUnload: function () {
 
 },
 
 /**
 * 頁(yè)面相關(guān)事件處理函數(shù)--監(jiān)聽用戶下拉動(dòng)作
 */
 onPullDownRefresh: function () {
 
 },
 
 /**
 * 頁(yè)面上拉觸底事件的處理函數(shù)
 */
 onReachBottom: function () {
 
 },
 
 /**
 * 用戶點(diǎn)擊右上角分享
 */
 onShareAppMessage: function () {
 
 }
})