<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<script>
var sum;
for(var i=0;i<=100;i++){
sum+=i;
}
console.log(sum);
</script>
</body>
</html>运行结果
