code: function bundleFiles(files, copy, version) {
      var node = new SourceNode(null, null, null, '');
  
      node.add(new SourceNode(null, null, null, copy + '(function (window, document, undefined) {'));
  
      for (var i = 0, len = files.length; i < len; i++) {
          var contents = fs.readFileSync(files[i], 'utf8');
  
          if (files[i] === 'src/Leaflet.draw.js') {
              contents = contents.replace(
                  new RegExp('drawVersion = \'.*\''),
                  'drawVersion = ' + JSON.stringify(version)
              );
          }
  
          var lines = contents.split('\n');
          var lineCount = lines.length;
          var fileNode = new SourceNode(null, null, null, '');
  
          fileNode.setSourceContent(files[i], contents);
  
          for (var j = 0; j < lineCount; j++) {
              fileNode.add(new SourceNode(j + 1, 0, files[i], lines[j] + '\n'));
          }
          node.add(fileNode);
  
          node.add(new SourceNode(null, null, null, '\n\n'));
      }
  
      node.add(new SourceNode(null, null, null, '}(window, document));'));
  
      var bundle = node.toStringWithSourceMap();
      return {
          src: bundle.code,
          srcmap: bundle.map.toString()
      };
  }
docs: Concatenate the files while building up a sourcemap for the concatenation, and replace the line defining L.version with the string prepared in the jakefile