How to test if a URL string is absolute or relative?

Question

How can I test a URL if it is a relative or absolute path in Javascript or jQuery? I want to handle accordingly depending if the passed in URL is a local or external path.

Answer 1

Nowdays, when a lot of services use protocol-relative URL (eg. //cdn.example.com/libary.js), this method is safer:

var isAbsolute = new RegExp('^([a-z]+://|//)', 'i');

if (isAbsolute.test(urlString)) {
  // go crazy here
}