Check if a JavaScript string is a URL

Question

Is there a way in JavaScript to check if a string is a URL?

RegExes are excluded because the URL is most likely written like stackoverflow; that is to s

Answer 1

2020 Update. To expand on both excellent answerd from @iamnewton and @Fernando Chavez Herrera I've started to see @ being used in the path of URLs.

So the updated regex is:

RegExp('(https?:\\/\\/)?((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|((\\d{1,3}\\.){3}\\d{1,3}))(\\:\\d+)?(\\/[-a-z\\d%_.~+@]*)*(\\?[;&a-z\\d%_.~+=-]*)?(\\#[-a-z\\d_]*)?$', 'i');

If you want to allow it in the query string and hash, use:

RegExp('(https?:\\/\\/)?((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|((\\d{1,3}\\.){3}\\d{1,3}))(\\:\\d+)?(\\/[-a-z\\d%_.~+@]*)*(\\?[;&a-z\\d%_.~+=-@]*)?(\\#[-a-z\\d_@]*)?$', 'i');

That being said, I'm not sure if there's a whitepaper rule disallowing @ in the query string or hash.