docs: function watchjs(sources, outdir, outfile, opt_options) {
    var bundler = watchify(browserify({
      entries: sources,
      debug: false,
      // Watchify options:
      cache: {},
      packageCache: {},
      fullPaths: true
    }));
  
    bundler.on('update', function() {
      gutil.log('recompiling js...');
      rebundle_(bundler, outdir, outfile, opt_options);
      gutil.log('finished recompiling js');
    });
    return rebundle_(bundler, outdir, outfile, opt_options);
  }