<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title> 事件</title>
<script type="text/javascript">
function count(){
var x=document.getElementById("txt1").value;
var y=document.getElementById("txt2").value;
var z=document.getElementById("select").value;
var result;
switch(z){
case "+":
result=parseFloat(x) +parseFloat(y);
break;
case "-":
result=parseFloat(x) - parseFloat(y);
break;
case "*":
result=parseFloat(x) * parseFloat(y);
break;
case "/":
result=parseFloat(x) / parseFloat(y);
}
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>