                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /JavaScript進階篇

就這樣了吧

<!DOCTYPE?html>
<html>
<head>
????<title>?事件</title>
????<script?type="text/javascript">
????????function?count(){
????????????num1?=?parseFloat(document.getElementById("txt1").value)
????????????num2?=?parseFloat(document.getElementById("txt2").value)
????????????opertor?=?document.getElementById("select").value
????????????var?sum;
????????????switch?(opertor)?{
????????????????case?"+":?sum?=?num1?+?num2;?break;
????????????????case?"-":?sum?=?num1?-?num2;?break;
????????????????case?"*":?sum?=?num1?*?num2;?break;
????????????????case?"/":?sum?=?num1?/?num2;?break;
????????????}
????????????document.getElementById("fruit").value?=?sum;
????????}

????</script>
</head>
<body>
<input?type='text'?id='txt1'?/>
<select?id='select'>
????<option?value='+'>+</option>
????<option?value="-">-</option>
????<option?value="*">*</option>
????<option?value="/">/</option>
</select>
<input?type='text'?id='txt2'?/>
<input?type='button'?onclick="count()"?value='?=?'?/>?<!--通過?=?按鈕來調用創建的函數，得到結果-->
<input?type='text'?id='fruit'?/>
</body>
</html>