                        課程
                    
                        /前端開發
                        
                            /JavaScript
                        
                        /JavaScript進階篇

運行得不到結果

<!DOCTYPE html>
<html>
?<head>
? <title> 事件</title> ?
? <script type="text/javascript">
?? function count()
?? {
?????? var t1=parseInt(document.getElementById("txt1").value);
??? //獲取第一個輸入框的值
?????? var t2=parseInt(document.getElementById("txt2").value);
?? ?//獲取第二個輸入框的值
????? var m=document.getElementById("select").value;
????? var result="";
????? switch (m)
????? {
????????? case "+":result=t1+t2;
????????? break;
????????? case "-":result=t1-t2;
????????? break;
????????? case "*":result=t1*t2;
????????? break;
????????? case "/"
????????? result=t1/t2;
????? }
?? ?//獲取選擇框的值
?? ?//獲取通過下拉框來選擇的值來改變加減乘除的運算法則
??? //設置結果輸入框的值
??? document.getElementById("fruit").value=result;
?? }
? </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' value=' = ' onclick="count()"/> 
?? <input type='text' id='fruit' />? ?
?</body>
</html>