How to validate url?

Question

I want to validate urls. It should accept:

http://google.com

http://www.google.com

www.google.com

google.com

I refer Regex to match URL

Answer 1

Simply prepend http:// if it's not there and then test.

if (inputURL.substring(0,7) != 'http://' && inputURL.substring(0,8) != 'https://') {
    inputURL = 'http://' + inputURL;
}

No large libraries required or anything, just a few lines of code.