超级简易的JS计算器实例讲解(实现加减乘除)

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>简单的计算器</title>
    <style> 
      body{
        margin: 0;
      }
      .tab{
        border: 3px solid black ;
        border-radius: 2px;
        border-collapse:collapse;
        width: 268px;
        height: 402px;
        margin: 100px auto;
      }
      
      .tr{
        height: 67px;
        width: 268px;
        border: 3px solid black ;
        text-align: right;
      }
      .tr1{
        width: 268px;
        height: 67px;
        border: 3px solid black ;
        text-align: center;
      }
      .tr2{
        width: 67px;
        height: 67px;
        border: 3px solid black ;
        text-align: center;
      }
        
      
    </style>
    <script>
      
      var s1 = "";
      var s2 = "";
      var s3 = "";
      var s4 = "";
      var s5 = "";
      function view(val){
        var a = document.getElementById(val);
        s1 = a.innerHTML;
        if(s1=="+" || s1=="-" || s1=="*" || s1=="/"){
          s3 = s1;
          s1 = "";
        }
        
        if(s3=="+" || s3=="-" || s3=="*" || s3=="/"){
          add2(s1);
          
        }
        
        if(s3==""){
          add1(s1);  
          
        }
        
        
        
        
      }
      function add1(s1){
        s2 = s2 + s1;
        show();
      }
      function add2(s1){
        s4 = s4 + s1;
        show();
      }
      
      function cal(){
        switch(s3){
          case "+":{
            s5 = (String)((parseFloat(s2)+parseFloat(s4)).toFixed(2));
            result.innerHTML = s5;
            break;
          }
          case "-":{
            s5 = (String)((parseFloat(s2)-parseFloat(s4)).toFixed(2));
            result.innerHTML = s5;
            break;
          }
          case "*":{
            s5 = (String)((parseFloat(s2)*parseFloat(s4)).toFixed(2));
            result.innerHTML = s5;
            break;
          }
          case "/":{
            s5 = (String)((parseFloat(s2)/parseFloat(s4)).toFixed(2));
            result.innerHTML = s5;
            break;
          }
        }
        
      }
      
      function show(){
        var result = document.getElementById("result");
        
        result.innerHTML = s2+s3+s4;
        
      }
      
      
      
    </script>
  </head>
  <body>
    <table class="tab">
      <tr class = "tr2">
        <td colspan="4">简易计算器</td>
      </tr>
      <tr class="tr">
        <td id="result" colspan="4" >  
        
        </td>
      </tr>
      <tr >
        <td id="+" class="tr1" onclick="view('+')">+</td>
        <td id="-" class="tr1" onclick="view('-')">-</td>
        <td id="*" class="tr1" onclick="view('*')">*</td>
        <td id="/" class="tr1" onclick="view('/')">/</td>
      </tr>
      <tr >
        <td id="7" class="tr1" onclick="view('7')">7</td>
        <td id="8" class="tr1" onclick="view('8')">8</td>
        <td id="9" class="tr1" onclick="view('9')">9</td>
        <td id="0" class="tr1" onclick="view('0')">0</td>
      </tr>
      <tr>
        <td id="4" class="tr1" onclick="view('4')">4</td>
        <td id="5" class="tr1" onclick="view('5')">5</td>
        <td id="6" class="tr1" onclick="view('6')">6</td>
        <td id="." class="tr1" onclick="view('.')">.</td>
      </tr>
      <tr>
        <td id="1" class="tr1" onclick="view('1')">1</td>
        <td id="2" class="tr1" onclick="view('2')">2</td>
        <td id="3" class="tr1" onclick="view('3')">3</td>
        <td id="=" class="tr1" onclick="cal()" >=</td>
      </tr>
    </table>
  </body>
</html>