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                        /JavaScript進(jìn)階篇

求大神幫忙，為什么錯(cuò)了

<title> 事件</title>?
? <script type="text/javascript">
?? function count(){
??? var result;??
??? var a1 = document.getElementById("txt1").value ;//獲取第一個(gè)輸入框的值
?var a2 = document.getElementById("txt2").value ;//獲取第二個(gè)輸入框的值
?var fu = document.getElementById("select").value;//獲取選擇框的值
?switch(fu){
?case "+":
?result = parseInt(a1) + parseInt(a2);
???? break;
?case "-":
?result = parseInt(a1) - parseInt(a2);
???? break;
?case "*":
?result = parseInt(a1) * parseInt(a2);
???? break;?//獲取通過下拉框來選擇的值來改變加減乘除的運(yùn)算法則
?case "/":
?result = parseInt(a1) / parseInt(a2);
??? }??? //設(shè)置結(jié)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>