<!DOCTYPE html>
<html>
<head>
<title> 计算器</title>
<script type="text/javascript">
function count(){
var a=document.getElementById("txt1").value;
var b=document.getElementById("txt2").value;
var c=document.getElementById("select").value;
var d;
switch(c){
case "+":
d=parseFloat(a)+parseFloat(b);
break;
case "-":
d=parseFloat(a)-parseFloat(b);
break;
case "*":
d=parseFloat(a)*parseFloat(b);
default:
d=parseFloat(a)/parseFloat(b);
}
document.getElement("fruit").value=d;
}
</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>
document.getElementById("fruit").value=d;
<input type='button' value=' = ' onclick="count()" />