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Building stealjs.building


Learn how to build an application or applications for production.

After installing StealJS and using steal to load the modules of your application, it's time to build them into combined and minified scripts that download fast in production.

StealJS uses steal.build to build an application into production files.

By default, steal.build combines and minfies all modules into a single JavaScript and CSS file. This may not be optimal for performance so this article includes some common enhancements.

Basic build

To build a JS file that uses steal (ex: myapp/myapp.js in quick example), simply run :

> ./js steal/buildjs myapp/myapp.js

This will produce:

  • myapp/production.js
  • myapp/production.css

_Notice: If you used JavaScriptMVC's generators to generate an application skeleton, you can likely run ./js APP/scripts/build.js.

Switch a page to load these production scripts by changing the page from loading steal/steal.js to steal/steal.production.js:

<script src="../steal/steal.production.js?myapp"></script>

Often, these pages are rendered by a server-side framework that knows if it is running in a production environment or not. It's common that a server-side template includes some logic to switch between loading the production or development versions of steal like:

<script src='../steal/steal<%= ENV == "PRODUCTION" ? 
        ".production" :
        "" %>.js?myapp'/>

Top loading CSS

Typically, you want to top-load CSS so styling is present before any content is shown to the page while bottom-loading JavaScript.

To make this happen, manually add a <LINK> tag that points to production.css and configure steal so that it knows production.css has already been loaded and run like:

  <link rel="stylesheet" type="text/css" href="production.css"/>
   ... CONTENT ...
     steal = {
       executed: ["myapp/production.css"]
   <script src="../steal/steal.production.js?myapp"></script>

Cache Busting

As you release new versions, you want to make sure the latest production files are used by the client. To do this, configure the [steal.config.suffix suffix] property. This is often a build number passed by the server-side template like:

   steal = {
     suffix: "<%= BUILD_NUMBER %>"
 <script src="../steal/steal.production.js?myapp"></script>

Loading scripts from a CDN.

Sometimes, you want to not package certain modules in the production files, but load those modules somewhere else. Use steal.config.shim to prevent the module from being packaged and steal.config.paths to indicate where to load it:

paths: {
  "jquery": "http://cdn.com/jquery.min.js",
shim: {
  "jquery": {packaged: false}

If you have multiple pages using the same resources, use the [#section_Buildingmultipleapps building multiple apps] technique.

Building multiple apps

If you have multiple pages that use many of the same resources, it's a good practice to combine the shared resources into a file or files that can be cached and used across multiple pages.

If multiple apps are passed to steal.build, it will:

  • calculate which modules are shared by which applications
  • bundle the shared modules into cachable packages
  • set each app's production.js to load the packages it depends on.

For example, the following lists appA's and appB's dependencies:

  • appA

    • module1
    • module2
  • appB

    • module1
    • module3


> ./js steal/build appA/appA.js appB/appB.js

Will produce the following 3 files with their contents listed in []:

  • appA/production.js [module2]
  • appB/production.js [module3]
  • packages/appA_appB.js [module1]

As the number of apps grows, so does the number of shared packages. For example, building 4 apps will produce 15 production and package files:

4 - a,b,c,d
3 - a,b,c; a,b,d; a,c,d; b,c,d
2 - a,b; a,c; a,d; b,c; b,d; c,d;
1 - a; b; c; d;

Each app could potentially load 8 scripts! To prevent this, you can specify a depth argument that limits the number of scripts to load like:

./js steal/build appA/appA.js ... -depth 3

Steal will combine packages minimizing the amount of extra resources each page loads. In our experience, a depth of 3 is optimal.

Progressive loading

steal.packages can be used to progressively load an application.

    if(newVal === "login"){
    } else if(newVal === "filemanager"){