index.js

function convert() {
  var left = document.getElementById('left_ta');
  var right = document.getElementById('right_ta');

  var left_value = left.value;

  //preprocessing for tf2toolbox BBCode
  if(left_value.search(/TF2Toolbox/gmi) != -1) {
    left_value = left_value
    .replace(/(\(List generated at .+?\[\/URL\]\))((?:.|\n)+)/gmi, '$2\n\n\n$1') //Move TF2Toolbox link to bottom
    .replace('(List generated at', '(List generated from')
    .replace(/[^\S\n]+\(List/gmi,'(List')
    .replace(/\[b\]\[u\](.+?)\[\/u\]\[\/b\]/gmi,'[b]$1[/b]\n') //Fix double emphasized titles
    .replace(/(\n)\[\*\]\[b\](.+?)\[\/b\]/gmi, '$1\[\*\] $2');
  }

  //general BBcode conversion
  left_value = left_value
    .replace(/\[b\]((?:.|\n)+?)\[\/b\]/gmi, '**$1**') //bold; replace [b] $1 [/b] with ** $1 **
    .replace(/\[\i\]((?:.|\n)+?)\[\/\i\]/gmi, '*$1*')  //italics; replace [i] $1 [/u] with * $1 *
    .replace(/\[\u\]((?:.|\n)+?)\[\/\u\]/gmi, '$1')  //remove underline;
    .replace(/\[s\]((?:.|\n)+?)\[\/s\]/gmi, '~~ $1~~') //strikethrough; replace [s] $1 [/s] with ~~ $1 ~~
    .replace(/\[center\]((?:.|\n)+?)\[\/center\]/gmi, '$1') //remove center;
    .replace(/\[quote\=.+?\]((?:.|\n)+?)\[\/quote\]/gmi, '$1') //remove [quote=] tags
    .replace(/\[size\=.+?\]((?:.|\n)+?)\[\/size\]/gmi, '## $1') //Size [size=] tags
    .replace(/\[color\=.+?\]((?:.|\n)+?)\[\/color\]/gmi, '$1') //remove [color] tags
    .replace(/\[list\=1\]((?:.|\n)+?)\[\/list\]/gmi, function (match, p1, offset, string) {return p1.replace(/\[\*\]/gmi, '1. ');})
    .replace(/(\n)\[\*\]/gmi, '$1* ') //lists; replcae lists with + unordered lists.
    .replace(/\[\/*list\]/gmi, '')
    .replace(/\[img\]((?:.|\n)+?)\[\/img\]/gmi,'![$1]($1)')
    .replace(/\[url=(.+?)\]((?:.|\n)+?)\[\/url\]/gmi,'[$2]($1)')
    .replace(/\[code\](.*?)\[\/code\]/gmi, '`$1`')
    .replace(/\[code\]((?:.|\n)+?)\[\/code\]/gmi, function (match, p1, offset, string) {return p1.replace(/^/gmi, '    ');})
    .replace(/\[php\](.*?)\[\/php\]/gmi, '`$1`')
    .replace(/\[php\]((?:.|\n)+?)\[\/php\]/gmi, function (match, p1, offset, string) {return p1.replace(/^/gmi, '    ');})
    .replace(/\[pawn\](.*?)\[\/pawn\]/gmi, '`$1`')
    .replace(/\[pawn\]((?:.|\n)+?)\[\/pawn\]/gmi, function (match, p1, offset, string) {return p1.replace(/^/gmi, '    ');});
  
  //post processing for tf2toolbox BBCode
  if(left_value.search(/TF2Toolbox/gmi) != -1) {
    left_value = left_value
    .replace('/bbcode_lookup.php))', '/bbcode_lookup.php) and converted to /r/tf2trade ready Markdown by Dum\'s [converter](http://jondum.github.com/BBCode-To-Markdown-Converter/)).') //add a linkback
    .replace(/\*\*.+?\*\*[\s]+?None[\s]{2}/gmi, ''); //remove empty sections

  }

  right.value = left_value;

}