<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>第一个javascript计算页面</title>
</head>
<body>
<script type="text/javascript">
function sum(a,b) {
if((typeof a)== "number" && (typeof b)== "number"){
return a+b;
}
alert("您输入的数据不合法");
}
var v1=sum();
alert(v1);
var v2=sum(10);
alert(v2);
var v3=sum(10,20);
alert(v3);
var v4=sum(false,"sun");
alert(v4);
</script>
</html>
原文：https://www.cnblogs.com/god1/p/12114206.html