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求大神幫忙看看，為什么顯示不了結(jié)果

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