Javascript截取字符串的url

<!DOCTYPE html>
<html lang="en">
<head>
		<meta charset="UTF-8">
		<title>Document</title>
</head>
<body>
		<script>
				var url = 'http://www.test.com';
				alert(url.substring(0,5));
		</script>
</body>
</html>

结果:

http:

从第1位(索引为0),截取长度为5的字符串