WeChat applet custom menu navigation to achieve staircase effect

const query = wx.createSelectorQuery()
query.select('.menu_nav').boundingClientRect(function(res) {
    let obj = {}
    if (res && res.top) {
        obj[item.attr] = parseInt(res.top)
    }
}).exec()

let arr = [
         { name: '.menu-nav', attr: 'menu_top', addNum: 0 },
         { name: '.panel1', attr: 'panel1_top', addNum: 0 },
         { name: '.panel2', attr: 'panel2_top', addNum: 0 },
         { name: '.panel3', attr: 'panel3_top', addNum: 0 },
         { name: '.panel4', attr: 'panel4_top', addNum: 0 },
     ]
     arr.forEach((item, i) => {
         wx.createSelectorQuery().select(item.name).boundingClientRect(function(res) {
             let obj = {}
             if (res && res.top) {
                 obj[item.attr] = parseInt(res.top)

                 if (item.addNum) {
                     obj[item.attr] += item.addNum
                 }
                 that.setData({
                     ...obj
                 })
             }

         }).exec()

     })

// Listen for page scrolling onPageScroll: function(e) {
     let hTop = parseInt(e.scrollTop)
     // Automatically switch menu let tab=0
      if (hTop >= (this.data['panel4_top'] - this.data.menu_top)) {
        tab=3
     }else if (hTop >= (this.data['panel3_top'] - this.data.menu_top)){
        tab=2
     }
     else if (hTop >= (this.data['panel2_top'] - this.data.menu_top)){
         tab=1
     }
     this.setData({
         tabIndex: tab,
     })
 },

// pages/index/index.js
Page({

  /**
   * Initial data of the page */
  data: {
    tabIndex: 0, //Current menu menuList: ['Menu 1', 'Menu 2', 'Menu 3', 'Menu 4'], //Navigation menu tabFixed: false, //Whether to position// The distance from the top of the initial page menu_top: 0,
    panel1_top: 0,
    panel2_top: 0,
    panel3_top: 0,
    panel4_top: 0,
  },

  /**
   * Life cycle function--listen for page loading*/
  onLoad: function (options) {

  },
  onShow:function (options){
    this.getTopDistance()
  },
  // Get the height from the top of the page getTopDistance() {
    let that = this
    let arr = [{
        name: '.menu-nav',
        attr: 'menu_top',
        addNum: 0
      },
      {
        name: '.panel1',
        attr: 'panel1_top',
        addNum: 0
      },
      {
        name: '.panel2',
        attr: 'panel2_top',
        addNum: 0
      },
      {
        name: '.panel3',
        attr: 'panel3_top',
        addNum: 0
      },
      {
        name: '.panel4',
        attr: 'panel4_top',
        addNum: 0
      },
    ]
    arr.forEach((item, i) => {
      wx.createSelectorQuery().select(item.name).boundingClientRect(function (res) {
        let obj = {}
        if (res && res.top) {
          obj[item.attr] = parseInt(res.top)

          if (item.addNum) {
            obj[item.attr] += item.addNum
          }
          that.setData({
            ...obj
          })
        }

      }).exec()

    })
  },
  // Navigation bar switch settings setSelectType(event) {
    let index = event.currentTarget.dataset.type
    this.setData({
      tabIndex: index,
    })
    let arr = ['panel1_top', 'panel2_top', 'panel3_top', 'panel4_top']
    let _this = this
    wx.pageScrollTo({
      scrollTop: _this.data[arr[index]],
      duration: 500
    })
  },
  // Listen for page scrolling onPageScroll: function (e) {
    let hTop = parseInt(e.scrollTop)

    // Does the menu need to be positioned at the top if (hTop > this.data.menu_top) {
      this.setData({
        tabFixed: true
      })
    } else {
      this.setData({
        tabFixed: false
      })
    }

    // Automatically switch menu if (hTop >= (this.data['panel4_top'] - this.data.menu_top)) {
      this.setData({
        tabIndex: 3,
      })
    }else if (hTop >= (this.data['panel3_top'] - this.data.menu_top)){
      this.setData({
        tabIndex: 2,
      })
    }
    else if (hTop >= (this.data['panel2_top'] - this.data.menu_top)){
      this.setData({
        tabIndex: 1,
      })
    }else{
      this.setData({
        tabIndex: 0,
      })
    }
  },
})

<view class="Main">
    <view class="head">
        I am the head area</view>
    <view class="{{tabFixed?'is-fixed':''}} menu-nav">
        <text wx:for="{{menuList}}" class="{{tabIndex==index?'is-select':''}}" bind:tap="setSelectType" data-type='{{index}}'>{{item}}</text>
        
    </view>
    <view class="content">
        <view class="panel1 panel">Page 1</view>
        <view class="panel2 panel">Page 2</view>
        <view class="panel3 panel">Page 3</view>
        <view class="panel4 panel">Page 4</view>
    </view>
</view>

.menu-nav {
  display: flex;
  align-items: center;
  justify-content: space-around;
  color: black;
  padding: 10px 0;
  width: 100%;
  background-color: white;
}

.is-select {
  color: red;
}

.head {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 40px;
  height: 120px;
  background-color: greenyellow;
}

.is-fixed {
  position: fixed;
  top: 0;
}

.panel {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
}

.panel1 {
  height: 800rpx;
  background-color: rebeccapurple;
}

.panel2 {
  height: 700rpx;
  background-color: blue;
}

.panel3 {
  height: 1000rpx;
  background-color: orange;
}

.panel4 {
  height: 1200rpx;
  background-color: pink;
}