Packify grunt task (in a gist just for now)

grunt.js

/*
 * grunt
 * https://github.com/cowboy/grunt
 *
 * Copyright (c) 2012 "Cowboy" Ben Alman
 * Licensed under the MIT license.
 * http://benalman.com/about/license/
 */

/*global config:true, task:true*/
config.init({
  lint: {
    all: ['grunt.js']
  },
  min: {
    'dist/project.min.js': ['src/project.js']
  },
  packify: {
    'dist/project.pck.js': ['dist/project.min.js']
  },
  jshint: {
    options: {
      curly: true,
      eqeqeq: true,
      immed: true,
      latedef: true,
      newcap: true,
      noarg: true,
      sub: true,
      undef: true,
      boss: true,
      eqnull: true,
      evil: true
    },
    globals: {
      file: true,
      log: true,
      option: true
    }
  }
});

// Default task.
task.registerTask('default', 'lint min packify');

task.registerBasicTask('packify', 'Pack some JavaScript nice and small', function(data, name) {
  var files = file.expand(data);
  // Concat specified files.
  var max = task.helper('concat', files);
  // Packify source.
  var packified = task.helper('packify', max);
  // Write packified source.
  file.write(name, packified);
  // Fail task if errors were logged.
  if (task.hadErrors()) { return false; }

  // Otherwise, print a success message....
  log.writeln('File "' + name + '" created.');
  // ...and report some size information.
  task.helper('packify_info', packified, max);
});

task.registerHelper('packify', function(src) {
  // Single quotes need to be escaped, so use double-quotes in your input
  // source whenever possible.
  var script = src.replace(/'/g, "\\'");
  // Replace any non-space whitespace with spaces (shouldn't be necessary).
  script = script.replace(/\s+/g, ' ');

  // Return number of chars saved by replacing `count` occurences of `string`.
  function getSavings(string, count) {
    return (string.length - 1) * (count - 1) - 2;
  }

  // Just trying to keep things DRY here... Let's match some patterns!
  function getReMatch(pattern, text) {
    var re = new RegExp(pattern.replace(/(\W)/g, '\\$1'), 'g');
    return [text.match(re) || [], re];
  }

  var potentials = {};
  var potentialsList = [];
  var map = '';
  var i, chunk, matches, savings, re, potential, char;

  // Look for recurring patterns between 2 and 20 characters in length (could
  // have been between 2 and len / 2, but that gets REALLY slow).
  for (var chunkSize = 2, len = script.length; chunkSize <= 20; chunkSize++) {
    // Start at the beginning of the input string, go to the end.
    for (i = 0; i < len - chunkSize; i++) {
      // Grab the "chunk" at the current position.
      chunk = script.substr(i, chunkSize);
      if (!potentials[chunk]) {
        // Find the number of chunk matches in the input script.
        matches = getReMatch(chunk, script)[0];
        // If any matches, save this chunk as a potential pattern. By using an
        // object instead of an array, we don't have to worry about uniquing
        // the array as new potentials will just overwrite previous potentials.
        if (getSavings(chunk, matches.length) >= 0) {
          potentials[chunk] = matches.length;
        }
      }
    }
  }

  // Since we'll need to sort the potentials, create an array from the object.
  for (i in potentials) {
    if (potentials.hasOwnProperty(i)) {
      potentialsList.push({pattern: i, count: potentials[i]});
    }
  }

  // Potentials get sorted first by byte savings, then by # of occurrences
  // (favoring smaller count, longer patterns), then lexicographically.
  function sortPotentials(a, b) {
    return getSavings(b.pattern, b.count) - getSavings(a.pattern, a.count) ||
      a.count - b.count ||
      (a.pattern < b.pattern ? -1 : a.pattern > b.pattern ? 1 : 0);
  }

  // Loop over all the potential patterns, unless we run out of replacement
  // chars first. Dealing with 7-bit ASCII, valid replacement chars are 1-31
  // & 127 (excluding ASCII 10 & 13).
  for (var charCode = 0; potentialsList.length && charCode < 127; ) {
    // Re-calculate match counts.
    for (i = 0, len = potentialsList.length; i < len; i++) {
      potential = potentialsList[i];
      matches = getReMatch(potential.pattern, script)[0];
      potential.count = matches.length;
    }

    // Sort the array of potentials such that replacements that will yield the
    // highest byte savings come first.
    potentialsList.sort(sortPotentials);

    // Get the current best potential replacement.
    potential = potentialsList.shift();

    // Find all chunk matches in the input string.
    chunk = potential.pattern;
    matches = getReMatch( chunk, script );
    re = matches[1];
    matches = matches[0];

    // Ensure that replacing this potential pattern still actually saves bytes.
    savings = getSavings(chunk, matches.length);
    if (savings >= 0) {
      // Increment the current replacement character.
      charCode = ++charCode === 10 ? 11 :
        charCode === 13 ? 14 :
        charCode === 32 ? 127 :
        charCode;
      // Get the replacement char.
      char = String.fromCharCode(charCode);
      if (option('debug')) {
        log.debug(charCode, char, matches.length, chunk, savings);
      }
      // Replace the pattern with the replacement character.
      script = script.replace(re, char);
      // Add the char + pattern combo into the map of replacements.
      map += char + chunk;
    }
  }

  // For each group of 1 low ASCII char / 1+ regular ASCII chars combo in the
  // map string, replace the low ASCII char in the script string with the
  // remaining regular ASCII chars, then eval the script string. Using with in
  // this manner ensures that the temporary _ var won't be leaked.
  var result = "" +
    "with({_:'" + script + "'})" +
    "'" + map + "'.replace(/.([ -~]+)/g,function(x,y){" +
      "_=_.replace(RegExp(x[0],'g'),y)" +
    "})," +
    "eval(_)";

  // Return the result if successful, otherwise false on failure.
  return eval(result.replace('eval(_)', '_')) === src || option('debug') ?
    result : false;
});

// Output some size info about the packified source.
task.registerHelper('packify_info', function(packified, max) {
  var color = packified.length < max.length ? 'green' : 'red';
  log.writeln('Uncompressed size: ' + String(max.length)[color] + ' bytes.');
  log.writeln('Packified size: ' + String(packified.length)[color] + ' bytes.');
});

Also, FWIW, I might put this in grunt. If I don't, I'll make it readily available to people. Either way, have fun!