<!DOCTYPE html>
<html>
<head>
<title> 事件</title>
<script type="text/javascript">
function count(){
var a = document.getElementById("txt1").value;
var b = document.getElementById("txt2").value;
var symbol = document.getElementById("select").value;
var result="";
switch(symbol)
case "+":
result = parseFloat(a) + parseFloat(b);
break;
case "-":
result = parseFloat(a) - parseFloat(b);
break;
case "*":
result = parseFloat(a) * parseFloat(b);
break;
case "/":
result = parseFloat(a) / parseFloat(b);
break;
//设置结果输入框的值
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()"/> <!--通过 = 按钮来调用创建的函数，得到结果-->
<input type='text' id='fruit' />
</body>
</html>
