一个块级作用域！
<!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>测试</title>
</head>
<body>
</body>
<script>
function ceshi(count) {
for( var i = 0; i < count; i ++ ) {
console.log(i); // 0,1,2,3,4,5,6,7,8,9
}
}
console.log(i);
ceshi(10);
</script>
</html>