EPUB core processing engine written in Javascript.

This is a software component used by the Readium Chrome extension and the "cloud reader" ( ).

Please see for more information about the underlying rendering engine.

You can try Readium here:


BSD-3-Clause ( )

See license.txt.



Initial setup:

  • git submodule update --init --recursive to ensure that the readium-js chain of dependencies is initialised (readium-shared-js and readium-cfi-js)
  • git checkout BRANCH_NAME && git submodule foreach --recursive "git checkout BRANCH_NAME" to switch to the desired BRANCH_NAME
  • npm run prepare:all (to perform required preliminary tasks, like patching code before building)
  • OR: yarn run prepare:yarn:all (to use Yarn instead of NPM for node_module management)

Note that in some cases, administrator rights may be needed in order to install dependencies, because of NPM-related file access permissions (the console log would clearly show the error). Should this be the case, running sudo npm run prepare:all usually solves this.

Note that the above command executes the following:

  • npm install (to download dependencies defined in package.json ... note that the --production option can be used to avoid downloading development dependencies, for example when testing only the pre-built build-output folder contents)
  • npm update (to make sure that the dependency tree is up to date)

Typical workflow:

No RequireJS optimization:

  • npm run http (to launch an http server. This automatically opens a web browser instance to the HTML files in the dev folder, choose index_RequireJS_no-optimize.html, or the *LITE.html variant which do include only the reader view, not the ebook library view)
  • Hack away! (e.g. source code in the src/js folder)
  • Press F5 (refresh / reload) in the web browser

Or to use optimized Javascript bundles (single or multiple):

  • npm run build (to update the RequireJS bundles in the build output folder)
  • npm run http:watch (to launch an http server. This automatically opens a web browser instance to the HTML files in the dev folder, choose index_RequireJS_single-bundle.html or index_RequireJS_multiple-bundles.html, or the *LITE.html variants which do include only the reader view, not the ebook library view)
  • npm run http (same as above, but without watching for file changes (no automatic rebuild))

Plugins integration:

When invoking the npm run build command, the generated build-output folder contains RequireJS module bundles that include the default plugins specified in readium-js-shared/plugins/plugins.cson (see the readium-js-shared/ documentation). Developers can override the default plugins configuration by using an additional file called plugins-override.cson. This file is git-ignored (not persistent in the Git repository), which means that Readium's default plugins configuration is never at risk of being mistakenly overridden by developers, whilst giving developers the possibility of creating custom builds on their local machines.

For example, the annotations plugin can be activated by adding it to the include section in readium-js-shared/plugins/plugins-override.cson.
This way, after invoking npm run http, the ./dev/index*.html demo apps can be used to create / remove highlighted selections in the web browser.

NPM (Node Package Manager)

All packages "owned" and maintained by the Readium Foundation are listed here:

Note that although Node and NPM natively use the CommonJS format, Readium modules are currently only defined as AMD (RequireJS).
This explains why Browserify ( ) is not used by this Readium project.
More information at and

Note: the --dev option after npm install readium-js can be used to force the download of development dependencies,
but this is kind of pointless as the code source and RequireJS build configuration files are missing.
See below if you need to hack the code.

How to use (RequireJS bundles / AMD modules)

The build-output directory contains common CSS styles, as well as two distinct folders:

Single bundle

The _single-bundle folder contains readium-js_all.js (and its associated source-map file, as well as a RequireJS bundle index file (which isn't actually needed at runtime, so here just as a reference)),
which aggregates all the required code (external library dependencies included, such as Underscore, jQuery, etc.),
as well as the "Almond" lightweight AMD loader ( ).

This means that the full RequireJS library ( ) is not actually needed to bootstrap the AMD modules at runtime,
as demonstrated by the HTML file in the dev folder (trimmed for brevity):


<!-- main code bundle, which includes its own Almond AMD loader (no need for the full RequireJS library) -->
<script type="text/javascript" src="../build-output/_single-bundle/readium-js_all.js"> </script>

<!-- index.js calls into the above library -->
<script type="text/javascript" src="./index.js"> </script>

<div id="viewport"> </div>

Multiple bundles

The _multiple-bundles folder contains several Javascript bundles (and their respective source-map files, as well as RequireJS bundle index files):

  • readium-external-libs.js: aggregated library dependencies (e.g. Underscore, jQuery, etc.)
  • readium-shared-js.js: shared Readium code (basically, equivalent to the js folder of the "readium-shared-js" submodule)
  • readium-cfi-js.js: Readium CFI library (basically, equivalent to the js folder of the readium-cfi-js submodule)
  • readium-js.js: this Readium code (see the js folder, which includes epub-fetch and epub-model source code)
  • readium-plugin-example.js: simple plugin demo
  • readium-plugin-annotations.js: the annotation plugin (DOM selection + highlight), which bundle actually contains the "Backbone" library, as this dependency is not already included in the "external libs" bundle.

In addition, the folder contains the full RequireJS.js library ( ), as the above bundles do no include the lightweight "Almond" AMD loader ( ).

Usage is demonstrated by the HTML file in the dev folder (trimmed for brevity):


<!-- full RequireJS library -->
<script type="text/javascript" src="../build-output/_multiple-bundles/RequireJS.js"> </script>

<!-- individual bundles: -->

<!-- readium CFI library -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-cfi-js.js"> </script>

<!-- external libraries -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-external-libs.js"> </script>

<!-- readium itself -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-shared-js.js"> </script>

<!-- simple example plugin -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-plugin-example.js"> </script>

<!-- annotations plugin -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-plugin-annotations.js"> </script>

<!-- readium js -->
<script type="text/javascript" src="../build-output/_multiple-bundles/readium-js.js"> </script>

<!-- index.js calls into the above libraries -->
<script type="text/javascript" src="./index.js"> </script>

<div id="viewport"> </div>

Note how the "external libs" set of AMD modules can be explicitly described using the bundles RequireJS configuration directive
(this eliminates the apparent opacity of such as large container of library dependencies):

<script type="text/javascript">
    baseUrl: '../build-output/_multiple-bundles'

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-cfi-js.js.bundles.js"> </script>

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-external-libs.js.bundles.js"> </script>

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-shared-js.js.bundles.js"> </script>

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-plugin-example.js.bundles.js"> </script>

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-plugin-annotations.js.bundles.js"> </script>

<script type="text/javascript" src="../build-output/_multiple-bundles/readium-js.js.bundles.js"> </script>

CSON vs. JSON (package.json)

CSON = CoffeeScript-Object-Notation ( )

Running the command npm run cson2json will re-generate the package.json JSON file.
For more information, see comments in the master package.cson CSON file.

Why CSON? Because it is a lot more readable than JSON, and therefore easier to maintain.
The syntax is not only less verbose (separators, etc.), more importantly it allows comments and line breaking!

Although these benefits are not so critical for basic "package" definitions,
here package.cson/json declares relatively intricate script tasks that are used in the development workflow.
npm run SCRIPT_NAME offers a lightweight technique to handle most build tasks,
as NPM CLI utilities are available to perform cross-platform operations (agnostic to the actual command line interface / shell).
For more complex build processes, Grunt / Gulp can be used, but these build systems do not necessarily offer the most readable / maintainable options.

Downside: DO NOT invoke npm init or npm install --save --save-dev --save-optional,
as this would overwrite / update the JSON, not the master CSON!


See separate API doc.