JavaScript实现简单加法计算器

<html>
  <head>
    <meta charset="utf-8">
    <title>计算器</title>
    <script>
      function myck(type){
        var num1 = document.getElementById("num1");
        var num2 = document.getElementById("num2");
        if(type==1){
          // 计算操作
          var result = parseInt(num1.value) + parseInt(num2.value);
          alert(result);
          document.getElementById("resultDiv").innerText ="最终计算结果："+ result;
        }else if(type==2){
    var result = parseInt(num1.value) - parseInt(num2.value);
             alert(result);
             document.getElementById("resultDiv").innerText ="最终计算结果："+ result;
   }
     else if(type==3){
     var result = parseInt(num1.value) * parseInt(num2.value);
     alert(result);
     document.getElementById("resultDiv").innerText ="最终计算结果："+ result;
      }
         else if(type==4){
        if(confirm("是否正确清空？")){
        // 清空
        num1.value = "";
        num2.value = "";
        document.getElementById("resultDiv").innerText="";
      }
           }
      }
    </script>
  </head>
  <body>
    <div style="margin-top: 100px;margin-left: 500px;">
      <span style="font-size: 60px;">计算器</span>   
    </div>
    <div>
      <div class="innerDiv" style="margin-left: 490px;">
        数&nbsp;&nbsp;字1：<input id="num1" type="number" placeholder="请输入数字1"> 
      </div>
    </div>
    <div>
      <div class="innerDiv" style="margin-left:490px;">
      数&nbsp;&nbsp;字2：<input id="num2" type="number" placeholder="请输入数字2">
     </div> 
    </div>
    <div>
      <div style="margin-left: 500px;" class="innerDiv">
        <input type="button" onclick="myck(1)" value="相&nbsp;&nbsp;加">
    <input type="button" onclick="myck(2)" value="相&nbsp;&nbsp;减">
    <input type="button" onclick="myck(3)" value="相&nbsp;&nbsp;乘">
        <input type="button" onclick="myck(4)" value="清&nbsp;&nbsp;空">
      </div> 
    </div>
    <div id="resultDiv">

    </div>
  </body>
  <style>
    .innerDiv{
      margin-left: 420px;
      margin-top: 20px;
    }
  </style>
</html>