WeChat applet implements simple calculator function

<view class='content'>
  <input value='{{calculation}}'></input>
  <view class='box'>
    <button class='yellow-color'>Backspace</button>
    <button class='yellow-color' bindtap='empty'>Clear screen</button>
    <button class='yellow-color'>❤</button>
    <button bindtap='add' data-text='+' class='yellow-color'>+</button>
  </view>

  <view class='box'>
    <button bindtap='add' data-text='9'>9</button>
    <button bindtap='add' data-text='8'>8</button>
    <button bindtap='add' data-text='7'>7</button>
    <button bindtap='add' class='yellow-color' data-text='-'>-</button>
  </view>

  <view class='box'>
    <button bindtap='add' data-text='6'>6</button>
    <button bindtap='add' data-text='5'>5</button>
    <button bindtap='add' data-text='4'>4</button>
    <button bindtap='add' class='yellow-color' data-text='*'>*</button>
  </view>

  <view class='box'>
    <button bindtap='add' data-text='3'>3</button>
    <button bindtap='add' data-text='2'>2</button>
    <button bindtap='add' data-text='1'>1</button>
    <button bindtap='add' data-text='/' class='yellow-color'>÷</button>
  </view>

  <view class='box'>
    <button bindtap='add' data-text='0'>0</button>
    <button bindtap='add' data-text='.'>.</button>
    <button>History</button>
    <button class='yellow-color' bindtap='res'>=</button>
  </view>


</view>

input {
  width: 95%;
  height: 250rpx;
  margin: 0 auto;
  margin-bottom: 20rpx;
  border-bottom: 1rpx solid #ccc;
}

.box {
  display: flex;
}
button {
  width: 20%;
  height: 150rpx;
  margin-bottom: 20rpx;
  line-height: 150rpx;
  background-color:rgb(0, 150, 250);
  color: white;
}

.yellow-color {
  background-color: rgb(247, 142, 24)
}

//index.js
//Get the application instance const app = getApp()

Page({
  data: {
    calculation:"",
    result:0,
    character:[], // operator symbol operand: [], // number temp:false
  },

  // Input box to enter data add:function(e) {
    let input = e.currentTarget.dataset.text;
    var that = this;
    if (input == '+' || input == '-' || input == '*' || input == '/') {
      this.data.temp = false; // Used to record whether the last time was an operator var item = 'character[' + this.data.character.length+ ']';
      this.setData({
        [item] :input
      }) 
    } else {
      var item = 'operand['+this.data.operand.length+']';
     
      if (that.data.temp) {
        // Get the previous value var res = 'operand[' + (this.data.operand.length-1) + ']'
        
        var ress = that.data.operand.length-1;
        var xyz = that.data.operand[ress] * 10 + parseInt(input);
        that.setData({
          [res]:xyz
        })
      } else {
        input = parseInt(input);
        that.data.temp = true;
        that.setData({
          [item]: input
        })
      }
    }
    // Put all the content into the display box this.setData({
      calculation:this.data.calculation+input
    })

  },

  // Calculate the answer res:function() {
    console.log(this.data.character.length);
    console.log(this.data.operand.length)
    var character_len = this.data.character.length;
    var operand_len = this.data.operand.length;
    console.log(operand_len - character_len)
    if (operand_len - character_len == 1) {
      this.data.result = this.data.operand[0];
      console.log("initial value"+this.data.result);
      for(var i=0;i<character_len;i++) {
        if(this.data.character[i] == '+') {
          this.data.result = this.data.result + this.data.operand[i + 1];

        }
        if (this.data.character[i] == '-') {
          this.data.result = this.data.result - this.data.operand[i + 1];

        }
        if (this.data.character[i] == '*') {
          this.data.result = this.data.result * this.data.operand[i + 1];

        }
        if (this.data.character[i] == '/') {
          this.data.result = this.data.result / this.data.operand[i + 1];

        }
        
      }
    } else {
      this.setData({
        Result: 'Input is incorrect, clear the data and re-enter'
      })
    }

    this.setData({
     calculation:this.data.result
    })
  },

  // Clear the screen empty:function() {
    this.setData({
      calculation: "",
      result: 0,
      character: [], // operator symbol operand: [], // number temp: false
    }
  }
})