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 '/' chars followed by a '.' (if they exist)
 reddit\.com # match 'reddit.com'
 (\/|$)      # match '/' or the end of the string
/i           # match case-insenitive

Close your if paren...

I've been using an alternative to RegEx by looking for the domain in the referrer

if (document.referrer.indexOf('reddit.com') >= 0) { alert('They came from Reddit.com'); }

EDIT: As thekingoftruth points out that doesn't work if reddit.com is included in an URL parameter so I've extended it a little. I've also added toLowerCase() as I spotted that in the RegExp above.

if (document.referrer.indexOf('?') > 0){
    if (document.referrer.substring(0,document.referrer.indexOf('?')).toLowerCase().indexOf('reddit.com') >= 0){
    alert('They came from Reddit');
    }
} else {
    if (document.referrer.toLowerCase().indexOf('reddit.com') > 0){
            alert('They came from Reddit');
    }
}