Checking the referrer

Try this:

if (ref.match(/^https?:\/\/([^\/]+\.)?reddit\.com(\/|$)/i)) {
  alert("Came from reddit");
}

The regexp:

/^           # ensure start of string
 http        # match 'http'
 s?          # 's' if it exists is okay
 :\/\/       # match '://'
 ([^\/]+\.)? # match any non "https://stackoverflow.com/" chars followed by a '.' (if they exist)
 reddit\.com # match 'reddit.com'
 (\/|$)      # match "https://stackoverflow.com/" or the end of the string
/i           # match case-insenitive