url_and_twitter_autolink.js

/**
 * Autolink urls in text
 * Optionally autolink usernames and hashtags in twitter text
 */

function autolink(txt){
    if(!txt) return;
    var txtstr = txt + ''; //make sure it's a string
    var url_re = /(http(s)?:\/\/[^\s)]+)/ig;
    return txtstr.replace(url_re, '<a href="$1" target="_blank" rel="nofollow">$1</a>') || txt;
}

function autolink_twitter(txt){
    txt = autolink(txt);
    var txtstr = txt + ''; //make sure it's a string
    var re = /(^|\W)(@([a-z0-9_]+[a-z0-9_-]*))/ig;
    txtstr = txtstr.replace(re, '$1<a href="http://twitter.com/$3" target="_blank" rel="nofollow">$2</a>');
    var txtarr = txtstr.split(' ');
    re = /(^|\W)(#([\w]+))/i;
    var outarr = [];
    var m = null;
    for(var i=0; i<txtarr.length;i++) {
        m = txtarr[i].match(re);
        if(!m || m.length < 2) {
            outarr[outarr.length] = txtarr[i];
            continue;
        }
        var n = '<a href="http://search.twitter.com/search?tag=' + encodeURIComponent(m[3]) + '" target="_blank" rel="nofollow">' + m[2] + '</a>';
        outarr[outarr.length] = txtarr[i].replace(re, '$1'+n);
    }
    return (outarr && outarr.length) ? outarr.join(' ') : txt;
}