var twitterScreenName = require('twitter-screen-name')
 
twitterScreenName('http://twitter.com/_alanshaw') // -> _alanshaw
twitterScreenName('https://www.twitter.com/_alanshaw') // -> _alanshaw
twitterScreenName('http://twitter.com/_alanshaw/status/695527644901801984') // -> _alanshaw
twitterScreenName('@_alanshaw') // -> _alanshaw
twitterScreenName('_alanshaw') // -> _alanshaw
// etc.
 
twitterScreenName('http://example.org/foo/') // -> null
twitterScreenName('toolongfortwitter') // -> null
// etc.