Mojito: FAQ

This page answers some of the most common questions we get about Mojito. For troubleshooting issues, see Mojito: Troubleshooting.




What languages can I use to develop mojits?

JavaScript is the programming language of Cocktails. All modules are written in JavaScript, and JavaScript only. Modules that require server-side execution do so through a server-side JavaScript execution engine.

Can I work on Mojito applications offline?

The tools used in developing mojit modules (mojits) work offline, without requiring access to networked resources. When networked (cloud) resources are required due to the modules own nature, e.g., retrieving data from a back-end service, Cocktails provides facilities to mock these resources and simulate their behavior with dummy (local) implementations.

Does Mojito work in a Windows environment?

Unfortunately, Mojito is only supported on Unix-based systems. We hope to support Mojito on Windows in the future, so please check the Mojito Releases Notes on GitHub for the latest updates.

Do I have to restart Mojito to see updates that I’ve made to my application?

No, you can use the development environment with certain configurations or use an external module such as nodemon or supervisor to start Mojito, which will automatically update any changes that you’ve made to your application.

I. Using the Development Environment

  1. In your application.json, add the configuration object with the settings property given the array [ "environment:development" ] with the configurations for staticHandling, viewEngine, and yui shown below.

        "settings": [ "master" ],
        "specs": {
          "frame": {
            "type": "HTMLFrameMojit",
            "config": {
              "deploy": true,
              "child": {
                "type": "foo"
        "settings": [ "environment:development" ],
        "staticHandling": {
          "forceUpdate": true
        "viewEngine": {
          "cacheTemplates": false
        "yui": {
          "config": {
            "combine": false


    Your application has to deploy code to the client, so deploy must be set to true.

  2. Modify your app.js to start with the context environment:development:

    libmojito.extend(app, {
        context: {
            runtime: 'server',
            environment: 'development'
  3. Open your application in a browser.

  4. Modify code in your binders or templates.

  5. Refresh your browser to see the updates in your application.


Although binder code and templates will be updated after you refresh your browser, resources, such as a model or controller, with a server or common affinity are executed in the Node.js environment, and therefore, will not get refreshed. You will need to restart your application to see changes. Also, meta data for modules, such as adding a module dependency to the requires array will not be reflected until you restart the application.

II. Using External Modules

You will need npm to install nodemon or supervisor. To use nodemon, you will need a script to start the server.

Follow the steps below to use nodemon:

  1. Install nodemon: $ sudo npm install nodemon -g

  2. In your Mojito application directory, create the file devel.js with the following:

    require('./server.js').listen(8666, null, function() {
      console.log('Nodemon will not honor the app port from the settings');
      console.log('The application is running under http://localhost:8666/');
  3. From your application directory, start Mojito with nodemon:

    $ nodemon devel.js

To use supervisor, follow these steps:

  1. Globally install supervisor.

    $ sudo npm install supervisor -g

  2. From a Mojito application directory, start Mojito with supervisor:

    $ supervisor -x node app.js

  3. View your application in a browser.

  4. In a separate terminal window, make changes to the source code of the application.

  5. Refresh the page to view the modified application.


supervisor will only update files with extensions node or js by default. To have supervisor watch files with other extensions, use the option -e or --extensions: $ supervisor -e js,json,html -x node app.js

Is the Mojito Y instance persistent across requests?

Yes, each mojit will have a Y instance that is persistent (by default) for every successive request. Computing YUI dependencies for every request negatively affects performance. You can change this behavior through the settings or you can deal with it at the mojit level, recreating the object.

Does Mojito support lazy loading?

Yes, the Mojito framework comes with the frame mojit LazyLoadMojit specifically for lazy loading. The LazyLoadMojit allows you to defer the loading of a mojit instance by first dispatching the LazyLoadMojit as a proxy to the client. From the client, LazyLoadMojit can then request Mojito to load the proxied mojit. This allows your Mojito application to load the page quickly and then lazily load parts of the page. See LazyLoadMojit to learn more.

Does Mojito have API methods for handling caching? If not, what’s the best way for Mojito applications to handle caching?

Mojito currently does not have any API methods for handling caching. Although there is no definitive solution for caching for Mojito, here are a few possible ways to cache for Mojito applications:

  • Client-Side Caching

  • Server-Side Caching (implementation depends on server)

    • Use the fs Node.js module to write to the file system.
    • Use one of the Node.js modules for caching: cradle, nodejs_redis, node-optimist, etc.
    • Implement a tried and tested caching solution such as memcached.

Can Mojito make runtime decisions to run client-side or server-side code?

Yes, but it’s up to the programmer to configure the application to be deployed to the client. Also, your application should have client and server versions, indicated by an affinity, of the controller, models, addons, etc., that you want to run on both the client and the server. To configure Mojito to deploy application code to the client, you set the deploy property of the application configuration to true. See Configuring Applications to Be Deployed to Client for more information.

Mojito determines the client device based on the HTTP header User-Agent or the value of the query string parameter device and then will render the appropriate view if it exists–it’s up to the developer to create the views. For example, if an iPhone is making a request, Mojito will render the view index.iphone.hb.html if it has been created. See Views: Naming Conventions for more information.

How can I improve the performance of my Mojito application?

The following sections offer some ideas about how to improve the performance of your Mojito application, but are by no means exhaustive. You should also review online articles about improving Node.js performance, such as Blazing fast node.js: 10 performance tips from LinkedIn Mobile written by software engineer Shravya Garlapati.

Don’t Add User Data to ac.context

The context property of the ActionContext object contains a small set of key-value pairs that define the run-time environment under which a mojit runs. These key-value pairs are used as a cache key. Adding your own key/values to ac.context will cause the cache to bloat.

As an alternative, you can share data using the following methods:

  • Parent mojits can share data with the child mojits by attaching data to the ActionContext object in the parent mojit’s controller. For example, in the parent mojit, you could add an object to ac.composite.command.params.body that the children can then access with ac.composite.command.params.body['{obj_name}'].
  • From the server and before mojits are executed, middleware can be used to share information about static handling and routing.
  • Assets and data can be shared through the template of a parent mojit or through a frame mojit such as HTMLFrameMojit that creates a parent template.

Rollup/Minify Assets

Rolling up and minifying assets will reduce the number of network calls and improve load time. For rolling up assets, we recommend that you use Shaker, which is a static asset rollup manager.

Mojito also allows you to configure your app to use rollups by setting the useRollups property in the application.json file to true as shown below:

"staticHandling": {
  "useRollups": true

You can also compile rollups, inline CSS, or views using the Mojito command-line utility. See the Compile System to learn how.

For minification, we recommend Shaker again. Other choices could be YUI Compressor or an npm module such as UglifyJS.

Use Lazy Loading

From the client, your Mojito application should lazy load assets as often as possible. For example, the YUI ImageLoader Utility can be used to help you lazy load images. You can even lazy load a mojit from the client using the LazyLoadMojit.

Can I start an application so that it listens to requests made to a specific IP address or hostname?

Although the Mojito CLI utility does not allow you to specify an IP address or hostname for your application to listen to when it’s started, you can modify the server.js file and start your application directory with node.

In the example server.js below, you pass the port and hostname to the listen method so that the application will listen to requests at the given hostname and port when you start the application with node server.js:

var mojito = require('mojito').createServer(),
    port = 8111,
    host = '';

 mojito.listen(port, host, function(err, app) {
   console.log('listening on %s:%d', host, port);


How do I configure Mojito to deploy my application to the client?

Binders always get deployed to the client, but to deploy your controller to the client, you need to use the HTMLFrameMojit and set the deploy field to true in the application.json file. See Deploying to Client for more details.

How do you configure mojits to run on the client?

Run Mojito at build time to generate the HTML page using mojito build html5app. This runs the Mojito infrastructure as if it were a running server instance and prints out the resulting HTML+JSON required to bootstrap a client-side mojit. Among other things, it leads down a path where it’s very hard to do incremental builds because the Web server abstraction makes it hard to do the timestamp resolution that incremental builds require. A better approach would be to allow people to hard-code the top-level mojit bootstrap code by publishing mojit creation APIs that can be called from the top level.

How do I configure the Mojito server to listen to specific port?

In app.js, you define the port or use the value of the exported variable PORT with the following line of code:

app.set(‘port’, process.env.PORT || 8666);

To define the variable process.env.PORT, you do the following from the CLI: $ export PORT={port_number}

What is the difference between ‘definition.json’ and ‘defaults.json’?

The definitions.json file stores the class-level mojit values and is ideal for storing metadata. The defaults.json file stories default configurations for your mojit instance that will be overridden if they are found in the application.json file. See Configuring Defaults for Mojit Instances and Mojit Configuration: Configuring Metadata for more information.


How do I get content for my mojits?

YQL is the preferred method for accessing data in Mojito applications. YUI 3 also has a YQL module that makes calling the YQL Web Service easy.

How is data shared among mojits?

You can create an application-level mojit that can share data with its children. Your application-level mojit would have a model to get data that can be stored data in a Model object. The child mojits can then access this data through the application-level mojit’s model.

How does a parent mojit send data to the template?

From the controller of the parent mojit, pass an object to ac.composite.done containing key-value pairs that can be added to the view template as Handlebars expressions. For example, the key foo shown below can be included in the template as the Handlebars expression . The expression will be replaced by the value ‘bar’ when the template is rendered.:

// Inside parent mojit
ac.composite.done({"foo": "bar"});

In Mojito applications, how are parameters passed from the controller to binders?

Your controllers can pass parameters to binders using the Data addon. The controller requires the Data addon and then uses the data object with the set method to set (or expose) data for the client code (binders or templates):'app_framework', "Mojito");

From the binder, the mojitProxy object can then access the data set by the controller from the data object with the get method:'app_framework');

The mojit’s template can access the set data through a Handlebars expression, so the index.hb.html could use to get the data set in the controller.

The Data addon also allows you to share page-level data, so that mojits on the page can share data through ac.pageData.set and ac.pageData.get or mojitProxy.pageData.get. See Sharing Data for more information and example code.

How can data be passed from a parent mojit to its child mojits?

Currently the only way to do this is to pass data to the children in either the children config or parameters. If you use ac.composite.execute you can create/modify the children configuration in code before calling ac.composite.execute. See ac.composite.execute for more information.

If you want to pass the data to the children in the parameters, you can do that with the ac._dispatch function. See ac._dispatch for more information.


What are binders and what do they do?

Binders are mojit code that is only deployed to the browser. A mojit may have zero, one, or many binders. The code can perform the following three functions:

  • allow event handlers to attach to the mojit DOM node
  • communicate with other mojits on the page
  • execute actions on the mojit that the binder is attached to

CSS/JavaScript Assets

How do I add assets templates?

You define the location of application-level or mojit-level assets in the application.json file. Once the location of your assets has been configured, you can statically add the path to the assets in your template. You can also add assets to your view using the Assets addon if your application is using the HTMLFrameMojit. See the Assets documentation for implementation details.

How are assets dynamically added to views?

The Assets addon allow you to dynamically add to your view. You need to use the HTMLFrameMojit, however, to use the Assets addon. See Using the Assets Addon for more information.

HTTP Headers/Responses

Can Mojito applications access the ‘request’ or ‘response’ instances of the Node.js classes ‘http.ServerRequest’ and ‘http.ServerResponse’?

Yes, the Mojito API has the ActionContext addon Http.server that has methods for getting the request and response instances of the Node.js classes http.ServerRequest and http.ServerResponse. From the ActionContext object ac shown below, you call http.getRequest and http.getResponse to get the request and response instances. See Class Http.server for more information.

var request = ac.http.getRequest();
var response = ac.http.getResponse();

Is it possible to access HTTP headers from a Mojito application?

Yes, the Mojito API has the ActionContext addon Http.server that allows you to get, set, and add HTTP headers. See Class Http.server for the available methods.


What is a mojit?

The basic unit of composition and reuse in a Mojito application. It typically corresponds to a rectangular area of a page and uses MVC.

Can mojits have child mojits?

Yes, you can configure your application to have mojits that have one or more child mojits. The parent mojit can execute the child mojits using the Composite addon. See Configuring Applications to Have Multiple Mojit and Composite Mojits.

You can also use frame mojits, such as HTMLFrameMojit that can execute one or more child mojits.

How do mojits share objects?

You create an application-level middleware or an ActionContext addon that all mojits can access. Your mojits can use this middleware or the ActionContext addon to share objects. See Creating Addons and Middleware for implementation details.

Can mojit instances be dynamically defined and then run?

You can run dynamically defined instances of mojits that you created with the Mojito command-line tool. You would create these instances in a mojit controller using the ActionContext object with either the _dispatch or execute methods. See Running Dynamically Defined Mojit Instances for more information.

Is there a way to make all of the resources, such as assets, addons, binders, models, of one mojit available to other mojits?

To make the resources of one mojit available to other mojits, you set the appLevel property in the definition.json file to true. Mojits wanting to use the resources of application-level mojit must include the YUI module of the application-level mojit in the requires array. See Configuring Metadata for more information.

Why does Mojito replace hyphens in the names of my mojits with underscores?

The ECMAScript syntax for Identifiers does not allow hyphens, so Mojito replaces them with underscores. See the section Identifier Names and Identifiers in the ECMAScript Documentation for the syntax rules for Identifier and IdentifierName.

Can I extend or re-use mojits?

Although inheritance isn’t supported in mojits, there are ways of re-using mojit definitions and configuration, application building blocks, and extending mojits.

The following sections offer a brief introduction to re-use and extension in Mojito as well as what cannot be re-used or extended.

Re-Using Mojit Definitions

You can re-use a mojit definition by using the specs.base property in application.json, so that mojit instance uses the same mojit definition of another mojit instance. This allows you to define a mojit instance once and have many instances use it.

For example, the mojit instances index_page and profile_page use the re-use the basic_page mojit definition in the application.json below:

    "settings": [ "master" ],
    "specs": {
      "basic_page": {
              "type": "HTMLFrameMojit",
              "config": {
                "child" : {
                 "config" : {
                   "children" : {
                     "header" : {
                       "type" : "Header"
                     "footer" : {
                       "type" : "Footer"
        "index_page": {
          "base" : "basic_page",
            "config": {
                    "title": "Home Page",
                    "child" : {
                      "type" : "Index"
        "profile_page": {
          "base" : "basic_page",
            "config": {
                    "title": "Your Profile",
                    "child" : {
                      "type" : "Profile"

Re-Using Application Building Blocks

In general, instead of extending a mojit, you would create a new mojit and then re-use building blocks such as YUI modules, assets, models, etc. For example, instead of having the stockProfile mojit extend the stockQuote mojit to get stock quotes, your stockProfile mojit could use the same addon, YUI module, or model to get the stock quotes.

See the following chapters on assets, extending Mojito, and models:

  • Assets - learn how to configure, access, and use the Assets addon.
  • Extending Mojito - learn how to create addons and add YUI modules.
  • Models - learn how to create and access models.

Requiring the Controller of Another Mojit

Starting with Mojito v0.5, you can create a new controller that requires the controller from another mojit. You simply require and merge the controller of the other mojit as shown below:

YUI.add('bar', function(Y, NAME) {

  Y.namespace('mojito.controllers')[NAME] = Y.merge(Y.mojito.controllers.Foo, {
    anotherNewAction: function (ac){
     // do something
    redefinedAction: function (ac) {
      // do something
      // you can also play with:
      // Y.mojito.controllers.Foo.redefinedAction.apply()

}, '0.0.1', {requires: ['foo']});

The same principle applies to binders and models.

What Can’t Be Re-Used/Extended?

The mojit configuration files definition.json and defaults.json cannot be re-used like the controller, binder(s), and model(s). In the near future, you will be able to re-use these configurations with the help of the import_settings directive in JSON and YAML files. Assets are also not extensible, so they will have to be included manually.


Does Mojito support view partials?

Mojito does not support partials, but you do have the following options for rendering data through a template:

  • use a child mojit instead of a view partial
  • render data from a binder through a specific template with the render method.
  • render data from the controller using ac.partial.render.

Not clear what view partials are? See view partial in the Mojito: Glossary.

Do I have to create separate mojits for different devices?

The platform’s capabilities allow mojits to be executed (and their results displayed) on every device in either set. For a module developer, the benefit is obvious: a single codebase that can address a wide range of devices. Mojits may still need to be customized for a specific device (or device class), however, to take advantage of device-specific capabilities. The platform does not perform an automated translation/degradation of HTML5 views to simpler layouts, for example.

How do I refresh the view on the client?

To refresh a view, you need to deploy a binder on the client. From the mojitProxy object of the binder, you can call the refreshView method to render a new DOM node for the current mojit and its children, as well as reattach all of the existing binders to their new nodes within the new markup. Because all binder instances are retained, state can be stored within a binder’s scope. See Refreshing Views and the MojitProxy Class in the Mojito API documentation for more information.

Can I use a different templating system other than Handlebars?

Mojito currently only comes with a Handlebars rendering engine, but you can add other rendering engines for templating systems such as EJS or Jade. See the View Engine documentation for implementation details.

Can the mojit controller specify which template should be rendered?

Yes, you can pass a view object as the second parameter to ac.done to specify which template should receive the data and be rendered. See Controllers: Specifying the View for details.


How do I change the logging levels for my Mojito application?

You can set log levels for your application using the yui.config object in application.json. You can also set default log levels using the yui.config object in the defaults.json at the application or mojit level.

See Logging for details and the code example Simple Logging.

Is there a way to exclude specific modules from logging on the client?

Yes, you can use the logExclude property of the yui.config object to exclude the logging of specified modules.

For example, the logging configuration set by yui.config below excludes logging from the module paging-binder-index:

    "yui": {
      "config": {
        "logExclude": "paging-binder-index",
        "logLevel": "info"

See Including and Excluding Modules From Logging for more information.

Can logging be configured to be different for the client and server?

Yes, the application.json configuration file uses the yui.config object for configuring logging. You can use contexts to customize logging for different runtime environments. For instance, you could use the "runtime:client" context to configure client-side logging and the "master" context to configure server-side logging. You can also use the properties logExclude and logInclude of the yui.config object to log or not log certain components of your application.

See config Object and the Log Configuration for implementation details.


Does the Mojito framework offer API methods or addons?

The Mojito framework provides API methods and addons through the ActionContext object. For an overview of the API and addons, see Mojito API Overview. To see the API specifications and the available addons, see the Mojito API documentation.

Can I repurpose or extend existing YUI modules?

Although Mojito application developers will have access to a library of modules, we realistically expect modules to require some tweaking before they can be re-purposed. Mojito, however, does offer facilities that make it possible and easy to extend existing modules.

A simple and common use case would be extending a built-in addon. For example, suppose you want to add a method to the Config addon that fetches other instance configurations. You could accomplish this in a number of different ways, several of which are listed below:

  • Add the method to the Config addon (mojito/lib/app/addons/ac/config.common.js) in the local copy of Mojito. This is not the recommended practice, but probably the easiest and fastest way to extend the addon.
  • Overwrite the Config addon by creating the addon config.common.js in {app_dir}/addons/ac or mojits/{mojit_name}/addons/ac with the same code as the built-in Config addon and then add your method. This requires more work and some redundancy, but your custom add will have the functionality of the Config addon as well as your additional method.
  • Create a custom addon that uses the same constructor as the built-in Config and add your new method. You’ll be able to access your method through the namespace you defined in your custom addon. You can use the Config addon for its functionality and your own addon for the additional method.
  • Create a custom addon that includes mojito-config-addon in the requires array. In the constructor of your addon, mix the prototype of the Config addon with the prototype of your addon, which might look something like the following: Y.mix({YourConstructore}.prototype,Y.namespace("").config.prototype); You can then add your own method, and your controller can use your addon that has the functionality of the built-in Config addon and your added method.

See the Addons section to learn how to create custom addons.