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Given that I’ve been working on compressing CSS and compressing HTML in PHP, it’s only natural that I’m interested in JavaScript compression too. I haven’t done much research on the topic — I’m sure there are better tools out there than the one I’ve cobbled together — but for the sake of it here’s my first take on JavaScript compression in PHP:

function slib_compress_script( $buffer ) {

  // JavaScript compressor by John Elliot <jj5@jj5.net>

  $replace = array(
    '#\'([^\n\']*?)/\*([^\n\']*)\'#' => "'\1/'+\'\'+'*\2'", // remove comments from ' strings
    '#\"([^\n\"]*?)/\*([^\n\"]*)\"#' => '"\1/"+\'\'+"*\2"', // remove comments from " strings
    '#/\*.*?\*/#s'            => "",      // strip C style comments
    '#[\r\n]+#'               => "\n",    // remove blank lines and \r's
    '#\n([ \t]*//.*?\n)*#s'   => "\n",    // strip line comments (whole line only)
    '#([^\\])//([^\'"\n]*)\n#s' => "\\1\n",
                                          // strip line comments
                                          // (that aren't possibly in strings or regex's)
    '#\n\s+#'                 => "\n",    // strip excess whitespace
    '#\s+\n#'                 => "\n",    // strip excess whitespace
    '#(//[^\n]*\n)#s'         => "\\1\n", // extra line feed after any comments left
                                          // (important given later replacements)
    '#/([\'"])\+\'\'\+([\'"])\*#' => "/*" // restore comments in strings
  );

  $search = array_keys( $replace );
  $script = preg_replace( $search, $replace, $buffer );

  $replace = array(
    "&&\n" => "&&",
    "||\n" => "||",
    "(\n"  => "(",
    ")\n"  => ")",
    "[\n"  => "[",
    "]\n"  => "]",
    "+\n"  => "+",
    ",\n"  => ",",
    "?\n"  => "?",
    ":\n"  => ":",
    ";\n"  => ";",
    "{\n"  => "{",
//  "}\n"  => "}", (because I forget to put semicolons after function assignments)
    "\n]"  => "]",
    "\n)"  => ")",
    "\n}"  => "}",
    "\n\n" => "\n"
  );

  $search = array_keys( $replace );
  $script = str_replace( $search, $replace, $script );

  return trim( $script );

}

It’s funny, but jQuery actually choked on my original function because it contains a few strings like “*/*”. To fix the problem I had to patch jQuery with “*/”+”*”, but then I decided to handle that case in my code. Of course jQuery comes pre-minified by tools much more sophisticated than mine. My tool compresses the 230 KB jQuery file to 150 KB, whereas the tool jQuery uses compresses the file to 90 KB. So I think I have my work cut out for me! It was a fun hack though.