How to use the npm.root function in npm

pluginSpecs: function(callback){
        exports.getPluginTests(callback);
      }
    },
    function(err, results){
      var files = results.coreSpecs; // push the core specs to a file object
      files = files.concat(results.pluginSpecs); // add the plugin Specs to the core specs
      console.debug("Sent browser the following test specs:", files.sort());
      res.send("var specs_list = " + JSON.stringify(files.sort()) + ";\n");
    });

  });


  // path.join seems to normalize by default, but we'll just be explicit
  var rootTestFolder = path.normalize(path.join(npm.root, "../tests/frontend/"));

  var url2FilePath = function(url){
    var subPath = url.substr("/tests/frontend".length);
    if (subPath == ""){
      subPath = "index.html"
    }
    subPath = subPath.split("?")[0];

    var filePath = path.normalize(path.join(rootTestFolder, subPath));
    // make sure we jail the paths to the test folder, otherwise serve index
    if (filePath.indexOf(rootTestFolder) !== 0) {
      filePath = path.join(rootTestFolder, "index.html");
    }
    return filePath;
  }

file = path.resolve(dir, file);
      stat = fs.lstatSync(file);
      if (stat.isDirectory() || stat.isSymbolicLink()) return;

      var ext = path.extname(file)
      , locale = path.basename(file, ext).toLowerCase();

      if ((ext == '.json') && languages.isValid(locale)) {
        if(!locales2paths[locale]) locales2paths[locale] = [];
        locales2paths[locale].push(file);
      }
    });
  }

  //add core supported languages first
  extractLangs(npm.root+"/ep_etherpad-lite/locales");

  //add plugins languages (if any)
  for(var pluginName in plugins) extractLangs(path.join(npm.root, pluginName, 'locales'));

  // Build a locale index (merge all locale data)
  var locales = {}
  _.each (locales2paths, function(files, langcode) {
    locales[langcode]={};

    files.forEach(function(file) {
     var fileContents = JSON.parse(fs.readFileSync(file,'utf8'));
      _.extend(locales[langcode], fileContents);
    });
  });

  return locales;

var ext = path.extname(file)
      , locale = path.basename(file, ext).toLowerCase();

      if ((ext == '.json') && languages.isValid(locale)) {
        if(!locales2paths[locale]) locales2paths[locale] = [];
        locales2paths[locale].push(file);
      }
    });
  }

  //add core supported languages first
  extractLangs(npm.root+"/ep_etherpad-lite/locales");

  //add plugins languages (if any)
  for(var pluginName in plugins) extractLangs(path.join(npm.root, pluginName, 'locales'));

  // Build a locale index (merge all locale data)
  var locales = {}
  _.each (locales2paths, function(files, langcode) {
    locales[langcode]={};

    files.forEach(function(file) {
     var fileContents = JSON.parse(fs.readFileSync(file,'utf8'));
      _.extend(locales[langcode], fileContents);
    });
  });

  return locales;
}

npm.load(config, function (err) {
		if (err) {
			return setImmediate(cb, err);
		}

		npm.root = path.join(dappPath, "node_modules");
		npm.prefix = dappPath;

		npm.commands.install(function (err, data) {
			if (err) {
				setImmediate(cb, err);
			} else {
				return setImmediate(cb, null);
			}
		});
	});
}

npm.load(config, function (err) {
		if (err) {
			return setImmediate(cb, err);
		}

		npm.root = path.join(dappPath, 'node_modules');
		npm.prefix = dappPath;

		npm.commands.install(function (err, data) {
			return setImmediate(cb, null);
		});
	});
};

npm.load(config, (err) => {
        if (err) {
            return setImmediate(cb, err);
        }

        npm.root = path.join(dappPath, 'node_modules');
        npm.prefix = dappPath;

        npm.commands.install(() => setImmediate(cb, null));
    });
};

npm.load(config, function (err) {
		if (err) {
			return setImmediate(cb, err);
		}

		npm.root = path.join(dappPath, 'node_modules');
		npm.prefix = dappPath;

		npm.commands.install(function (err, data) {
			return setImmediate(cb, null);
		});
	});
};