gsub.coffee

gsub = (source, pattern, replacement) ->
  unless pattern? and replacement?
    return source

  result = ''
  while source.length > 0
    if (match = source.match(pattern))
      result += source.slice(0, match.index)
      result += replacement
      source  = source.slice(match.index + match[0].length)
    else
      result += source
      source = ''

  result

gsub.js

gsub = function(source, pattern, replacement) {
  var match, result;
  if (!((pattern != null) && (replacement != null))) {
    return source;
  }
  result = '';
  while (source.length > 0) {
    if ((match = source.match(pattern))) {
      result += source.slice(0, match.index);
      result += replacement;
      source = source.slice(match.index + match[0].length);
    } else {
      result += source;
      source = '';
    }
  }
  return result;
};