The Shaker recipe is one part convention and one part configuration. The convention lies in the name you use for your resources (assets, binders, controllers, etc). The configuration lies in a mojit or application’s shaker.json file, which defines rollups and their contents.

We will see every feature/use case that Shaker can handle. Also, to clarify more all use cases, you can find a lot of examples here.

Contextualize: Context Dimensions

First we need to understand how we can contextualize assets in Mojito, and then how we can leverage this process with Shaker.

How It Works Out-of-the-Box in Mojito

In Mojito, we have a context for every request. This context has properties like language, region, device, bucket, and any other synthetic dimension that we could potentially add.

Giving a particular dimension, we may want to do different things. For example, if I’m on an iPhone, I may want mobile-specific CSS, or I may want to execute a different controller. In order to do that, Mojito has selectors. For every particular set of attributes on a context you can define a selector. This is what it looks like in your application.json:

  "settings": ["device:iphone"],
  "selector": "iphone"

Creating a resource sensitive to that selector is as simple as adding the selector to the file name:

  • controller.iphone.common.js - iphone is the selector
  • myview.bucket4.client.js - bucket4 is the selector
  • binder.tablet.js - tablet is the selector

Properly configured, Mojito will pick the right version of your resources at runtime.

Note that in Mojito, selectors only work for JavaScript files; they will not have any effect on CSS files. Shaker will take care of that, and we will show how in the next section. ‘ .. _context-do:

What Shaker Does with the Context

Using Mojito’s selector feature, we can bundle the right resources for a context on the client without negatively affecting performance.

At build time, Shaker will analyze the application using the Mojito Store API and will generate all the possible combinations that the application is aware of. This applies not only for JavaScript, but for CSS as well. Moreover, we need to serve different CSS for different actions.

Example of contextualizing for a Mojito with two actions and two possible devices:

Mojito with two actions and two possible devices.

In Mojito, all the resources are YUI Modules, which means that in addition to knowing which resources we will choose, we can also know in advance the dependencies that those modules require. With those two features, we can ensure that the bundle contains exactly the resources we need.

JavaScript Calculation

Because we are using the YUI module pattern for our resources, at build time, we can analyze the dependencies of a mojit for every given context and action. For example, this is the controller module of a regular mojit:

YUI.add('Main', function(Y, NAME) {
}, '0.0.1', {requires: ['mojito','mojito-assets-addon', 'mojito-models-addon', 'MainModelFoo']});

We know that when this mojit gets dispatched it will need a model resource called MainModelFoo, so we can compute that ahead of time and serve everything rolled up.

In mojito@0.5.x, a new feature was introduced where all the needed dependencies will be fetched and combo loaded automatically for us. We can configure Shaker to serve this combo load from a CDN (if you have a CDN which support combo loading), and even prefetch some of the dependencies combining mojit bundles.


If you are running an earlier version than Mojito v0.5.x, Shaker will automatically load the JavaScript dependencies for you.

CSS Selector Naming Rules

After reading and understanding the previous sections, let’s summarize the protocol that Shaker follows to deliver CSS:

  • Every CSS file with no selector (e.g., foo.css) will be considered common, therefore, will be included in each bundle within the mojit.
  • If a file has selector (e.g., foo.iphone.css), it will be included when the context matches.
  • If two files have the same name but different selectors (e.g., foo.css, foo.iphone.css) the correct one will be chosen. We call this versioning.
  • If a file name matches the view name, the CSS will be included only when the context and the executed action match (serve the assets for the right actions).

Generating Mojit Rollups: Shaker Metadata

Assuming that the assets of your mojits have been named correctly (see sections above), Shaker will be ready to analyze your application and bundle them.

When running Shaker, it will go over all the JavaScript and CSS resources for each mojit, checking dependencies (in the case of YUI modules), and based on the context, the configuration you provided (we will see more about those in the next section), it will construct the list or resources that each bundle will contain.

This information will be stored in a file called shaker-metadata, which will be used at runtime to know which bundles to serve.

Metadata generated by Shaker for a mojit with two actions:

"mojits": {
    "Main": {
        "index": {
            "js": [
            "css": [
        "other": {
            "js": [
            "css": [

We will see in the next sections how to customize the content of the rollups (minification, deployment to CDN, bootstrapping, etc.) through configuration.

Environment and Context Configuration

Shaker allows you to roll up your assets and deploy them in a variety of ways based on the environment context. For example, in production, you would like to minify your rollups and upload them to a CDN, whereas, on your development machine, you may only want to lint them and serve them separately.

All that is necessary is to provide a shaker configuration object for each
environment in your application.json file. The shaker object specifies what task

to run and any additional settings the task depends on.

Example: Sample application.json shaker setup using several environments:

    "settings": ["master"]
    "shaker: {
        //default configuration
}, {
    "settings": ["environment:test"],
    "shaker": {
        "task": "local"
        "lint": false,
        "minify": true,
        "rollupConfig": {
            bundleViews: false,
            bundleController: false
}, {
    "settings": ["environment:stage"],
    "shaker": {
        "task": "s3",
        "config": {
            "client": {
                "key": "<key>",
                "secret": "<secret>",
                "bucket": "<bucket>"

The previous configuration will give us three different types of execution environments. To build a particular environment, run the shaker command like so: mojito shake --context environment:<env> After running Shaker, start your Mojito application normally.

The following sections offer commands for deploying assets in different environments.

Deploying Raw (No Rollups, Developer Mode)

mojito shake

Deploying Locally (Rollups, Test Mode)

mojito shake --context environment:test

Deploying to S3 (Amazon CDN, Staging)

mojito shake --context environment:stage

Shaker Settings

As you saw in the code example above, for every environment we can set a different configuration for Shaker. These are some of the options we saw in the application.json example:

  • task - {string} Name of task to execute (local, s3, raw, etc.). Defaults to raw when running in development mode.
  • lint - {boolean} Run lint on application files. The default is true.
  • minify - {boolean} Minify JS and CSS. Defaults to true.
  • rollupConfig - {Object} It tells Shaker which parts to deploy to the client (binders, views, controllers, or all of them).

For all the options available in Shaker, see Shaker Configuration API.

Bundling Mojits Together

In the previous sections, we covered how Shaker works to create rollups for every mojit. Thus, the client we will have to fetch at least one CSS rollup/request per mojit and the request necessary for the JavaScript.

When there are too many mojits to execute, we should combine all the rollups in one to serve all the CSS at once and remove the overhead of multiple connections. To address this problem, Shaker defines what we call high-coverage mojits and low-coverage mojits, which we will discuss next.

High-Coverage Mojits

Definition: Ability to define ahead of time which mojits to bundle together so we just require one request for the first flush of the page.

Earlier, we saw that Shaker will build rollups for every mojit and for every possible set of configuration our application supports, which will reduce considerably the number of requests. But if we have a lot of mojits to dispatch and flush to the client, we will still end up doing a lot of CSS and JavaScript requests.

In this situation, Shaker allow us to define what we call high-coverage mojits. For every route defined in our application, we can tell Shaker which mojits are most likely to be loaded and then bundle all them together. The following is the syntax for bundling high-coverage mojits:

    "routeBundle": {
    //we define for each route which mojits we want to bundle together
        "foo": [
        "bar": [

At build time, Shaker will analyze routeBundle and generate the specific rollups for you. Note that all these rollups will be context specific, so it ships only what we need for a given context.

Low-Coverage Mojits

Definition: Load (lazily/dynamically) a mojit with its own JavaScript and CSS bundle.

Low-coverage mojits are all the mojits which are not defined in routeBundle. Shaker has to provide as well as bundle independent mojits that may be loaded after the page has already been rendered or when the user clicks a link that triggers the dispatch of a new mojit.

If there are no high-coverage bundles, the default behavior is to load the mojits as low coverage.

Because the Mojito v0.5.x handles the JavaScript with a local combo load, the only problem when not specifying high-coverage mojits is the number of CSS requests that need to be made.

Bundling Parts of a Mojit: rollupConfig

Going back to the bundles, we saw which resources to take into account, how to manage the dependencies, and how to select the right resources based on the context. We still, however, have to define which parts are going to be included.

So, depending on the application needs, we may want to ship only the minimum amount of JavaScript to the page (the binders and the bare-bone Mojito client code), or we may want to ship absolutely everything (controller, binders, dependencies, views, langs, etc.).

Shaker has to provide a way to select which components you want to rollup for every mojit. We could define this configuration at the application level, if we want to share all the configuration across mojits, or we can define small configuration files in each mojit to override which parts to bundle.

The configuration API will look something like:

"shaker": {
    "rollupConfig": {
          "bundleViews": false,
          "bundleController": false

With that, we can customize the parts we will include in the bundles. Note that Shaker should also provide a way to bundle all components together, so offline applications have almost no configuration.

Inlining Code

Sometimes we need to execute JavaScript or load CSS styles as quickly as possible to give our users a good user experience. In Mojito v0.5.x, you can inline code using the core APIs, but you will have to hard-code the code into your controllers, and this is not really ideal.

In Shaker, we came up with an automated way to do this. You just have to create a file with a special the selector shaker-inline in your mojit, and this file will be inline and served when the mojit is dispatched. Given that a mojit can have different behavior depending on the action, inlining is also sensible to the action, so if the name of your inline file matches an existing action in your mojit, it will be only inlined when the action matches at runtime.

By default, the code is inlined at the bottom of the page, before the Mojito client code is executed. If you want to inline the code right after the HTML generated by a particular mojit, you just have to include in your controller a dependency called shaker-inline. See examples about inlining in the Shaker App Example.

Summary example:

  • myInline.shaker-inline.css - this will be inlined for any action within the mojit.
  • mojitAction1.shaker-inline.js - Assuming that there is an action with his corresponding view called mojitAction1, the code will be inlined at runtime when mojitAction1 is executed.
  • myInline.iphone.shaker-inline.js - this will be inlined when the context (in this case iphone) matches at runtime.
YUI.add('MainController', function(Y, NAME) {
// My controller code
}, '0.0.1', {requires: ['mojito', 'shaker-inline-addon']});

Dynamic & Parallel Bootstrap

By default, the <script src=...></script> tag is evil! The browser must halt parsing the HTML until the script is downloaded and executed (since the script might call document.write() or define global variables that the scripts depend on). Images and style sheets that come after the script tag don’t start downloading until after the script has finished downloading and executing. External scripts typically make the page load much more slowly, which is why NoScript has become so popular.

W3C introduced the defer attribute to solve the problem. If you use <script defer src=...></script>, do not call document.write(). A deferred external script will start downloading immediately but won’t execute until after the page is rendered. The problem with defer is that the W3C HTML5 draft has removed defer from inlined scripts due to execution order guarantee, and also defer is not supported in some browsers.

The alternative we suggest is to dynamically load scripts. Here is a snippet illustrating how to dynamically load scripts:

  (function() {
    var script = document.createElement('script');
    script.src = '...';
    var s = document.getElementsByTagName('script')[0];
    s.parentNode.insertBefore(script, s);

Shaker implements, as a configuration option, a mechanism that dynamically loads the JavaScript bundles. Moreover, because we don’t control the order anymore, we implemented a special bootstrap to make sure YUI gets bootstrapped correctly. If you want to use the optimized bootstrap into your Mojito application, just add the option optimizeBootstrap: true in your Shaker configuration.

K-Weight Splitting

We have discussed high-coverage bundles and also Rollup configuration in the previous sections. Both can result in gigantic rollups that will require a significant amount of time to load.

Because we have dynamic script loading and a mechanism that guarantees the order, one other feature that Shaker provide is the ability to split those bundles into chunks that can be loaded in parallel. Shaker provides an API to define the threshold for the size of the chunks. Then, at build time, Shaker will split the rollup so we can optimize the loading time.

"shaker": {
    // This are the default values:
    "ksplit": {
        "weight": 100 // the kb limit for splitting
        "threshold": 20 // the percentage of threshold to split the rollup

The properties of ksplit specifies that Shaker should chunk files bigger than 100kb with a margin of 20%. In other words, files will be split into pieces with a size between 80kb and 120kb. You can set ksplit:true to work with the default values.