微信小程序官方动态自定义底部tabBar的例子

"tabBar": {
 "custom": true,//这个要有， 前面都提到过，注释要删了
 "color": "#7A7E83",
 "selectedColor": "#351f",
 "borderStyle": "black",
 "backgroundColor": "#ffffff",
 "list": [
  {
   "pagePath": "pages/index1/index1",
   "iconPath": "/image/home.png",
   "selectedIconPath": "/image/home1.png",
   "text": "首页1"
  },
  {
   "pagePath": "pages/mine1/mine1",
   "iconPath": "/image/user.png",
   "selectedIconPath": "/image/user1.png",
   "text": "我的1"
  },
  {
   "pagePath": "pages/index2/index2",
   "iconPath": "/image/home.png",
   "selectedIconPath": "/image/home1.png",
   "text": "首页2"
  },
  {
   "pagePath": "pages/mine2/mine2",
   "iconPath": "/image/user.png",
   "selectedIconPath": "/image/user1.png",
   "text": "我的2"
  }
 ]
},//这个
"usingComponents": {}

//app.js
App({
 onLaunch: function () {
 },
 globalData: {
  userInfo: null,
  list:[] //存放tabBar的数据
 }
})

custom-tab-bar/index.js

const app =getApp();
Component({
 data: {
  selected: 0,
  color: "#7A7E83",
  selectedColor: "#ff6700",
  list: [] //tabBar的数据
 },
 lifetimes: {
  //组件的生命周期函数
  attached() {
   this.setData({
    list: app.globalData.list
   })
  },
 },
 methods: {
  switchTab(e) {
   const data = e.currentTarget.dataset
   const url = data.path
   wx.switchTab({url})
   this.setData({
    selected: data.index
   })
  }
 }
})

<button bindtap='tab1'>进入tab1</button>
<button bindtap='tab2'>进入tab2</button>

 tab1: function() {
  app.globalData.list = [{
    "pagePath": "/pages/index1/index1",
    "iconPath": "/image/home.png",
    "selectedIconPath": "/image/home1.png",
    "text": "首页1"
   },
   {
    "pagePath": "/pages/mine1/mine1",
    "iconPath": "/image/user.png",
    "selectedIconPath": "/image/user1.png",
    "text": "我的1"
   }
  ]
  wx.switchTab({
   url: '../index1/index1',
  })
 },
 tab2: function() {
  app.globalData.list = [{
    "pagePath": "/pages/index2/index2",
    "iconPath": "/image/home.png",
    "selectedIconPath": "/image/home1.png",
    "text": "首页2"
   },
   {
    "pagePath": "/pages/mine2/mine2",
    "iconPath": "/image/user.png",
    "selectedIconPath": "/image/user1.png",
    "text": "我的2"
   }
  ]
  wx.switchTab({
   url: '../index2/index2',
  })
 }

//添加选中效果
if (typeof this.getTabBar === 'function' &&
   this.getTabBar()) {
   this.getTabBar().setData({
    selected: 0 //这个数是，tabBar从左到右的下标，从0开始
   })
  }