<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var f= document.getElementById("txt1"）.value;
alert(f)
}
</script>
</head>
<body>
<input type='text' id='txt1' value=""/>
<select id='select'>
<option value='+'>+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<input type='text' id='txt2' />
<input onclick="count()" type='button' value=' = ' /> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
var f= document.getElementById("txt1"）.value;这里括号错了，改成英文的即可
var f= document.getElementById("txt1").value;感谢 感谢