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                        /JavaScript進階篇

各位大佬幫我看看這個怎么運行不出來額

<!DOCTYPE html>
<html>
?<head>
? <title> 事件</title> ?
? <script type="text/javascript">
?? function count(){
????? ?
??? var oTxt1= document.getElementByid("txt1").value; //獲取第一個輸入框的值
??? var oTxt2 = document.getElementByid("txt2").value;//獲取第二個輸入框的值
?? ?var oSlt =document.getElementByid("select").value;//獲取選擇框的值
?? ?var result = "";//獲取通過下拉框來選擇的值來改變加減乘除的運算法則
??? switch(oSlt)
?? ?{
??????? case"+":
??????????? result = parseInt(oTxt1) + parseInt(oTxt2);
??????????? break;
??????? case"-":
??????????? result = parseInt(oTxt2) - parseInt(oTxt2);
??????????? break;
??????? case"*":
??????????? result = parseInt(oTxt1) * parseInt(oTxt2);
??????????? break;
??????? default:
??????????? result = parseInt(oTxt1) / parseInt(oTxt2);
??????????? break;
??? }//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=' = ' /> 
?? <input type='text' id='fruit' />? ?
?</body>
</html>