JS验证是否为URL

网上很多的方法都不正确！！

1 function isUrl(str) {
2         var v = new RegExp('^(?!mailto:)(?:(?:http|https|ftp)://|//)(?:\S+(?::\S*)?@)?(?:(?:(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[0-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\u00a1-\uffff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)(?:\.(?:[a-z\u00a1-\uffff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)*(?:\.(?:[a-z\u00a1-\uffff]{2,})))|localhost)(?::\d{2,5})?(?:(/|\?|#)[^\s]*)?$', 'i');
3         return v.test(str);
4     }

这是提取自：npm包 async-validator的源码。