code: function moduleSize(id, paths) {
      var path = id;
      var extension = '.js';
      // Use `paths:` to resolve an alias.
      if (paths[id]) {
          path = paths[id];
      }
      // Does the dependency reference a plugin?
      if (path.indexOf('!') !== -1) {
          // Split into plugin and path.
          var pathParts = path.split('!');
          // Often, the plugin maps to the extension it handles.
          extension = '.' + pathParts[0];
          path = pathParts[1];
      }
      // Try to get the file at the path.
      var stats;
      try {
          stats = fs.statSync(path);
          return stats['size'];
      }
      catch(e) {}
  
      // Didn't find it? Let's try again with the extension added.
      if (path.slice(-extension.length) !== extension) {
          path = path + extension;
      }
      try {
          stats = fs.statSync(path);
          return stats['size'];
      }
      catch(e) {}
  
      // Still didn't find the file.
      return null;
  }
docs: Returns the size of a module given its ID.
  At best this can be considered an estimate because it will return the
  size before compression, and doesn't take into consideration the effect
  of plugins.
  If the module cannot be resolved to a file, returns null.