epub js

ePUB.js vs Readium.js – A Detailed Comparison (2024)

ePUB is a widely used and easily convertible eBook format, thereby making ePUB reading systems popular. They allow users to access digital books using an app, device, or online service to easily open, read, and navigate the content.

As a comprehensive reference system for ePUB that promotes digital publications for the Open Web, ePUB.js and Readium.js are two of the main reading system options that play a crucial role in digital publishing

Table of Contents – 

What is ePUB.js?

ePUB.js is an open-source Javascript library that allows any web page to easily render ePUB documents on any device with a modern browser.

It contains a flexible rendering engine and offers a simple interface for common eBook functions such as pagination, styling, and persistence without developing a dedicated plugin or application.

Key Features

Among the critical features of ePUB.js include-

  • Different Rendering Methods

ePUB.js offers two different render methods, including default and continuous. While the default method only displays a single section at a time, the continuous mode displays multiple sections as per the need to fill the screen and preload the next section offscreen. This enables users to seamlessly swipe/scroll between pages on mobile and desktop.

  • Feature Hooks

Similar to plugins, ePUB.js implements events into which you can be easily hooked. This allows users to interact with and manipulate the contents of the book. An example of this functionality is directly loading videos from YouTube links before implementing annotation or displaying a chapter’s contents.

Other features of ePUB.js include-

  • Allows searching for a specific text in the book 
  • Enables users to generate and get page numbers
  • Allows loading a book from a file input
  • Can add a page transition animation
  • Allows keyboard arrow keys to control the pages
  • With this javascript library, users can easily swipe the pages on touchscreens


How to Automate PDF to ePub3 Conversion

What is Readium?

Readium is essentially a Chrome browser extension for reading ePUB eBooks and is available for free. You can easily view your eBook in Readium with just a few clicks.

Readium.js is a JavaScript library and viewer (readium-js-viewer/CloudReader) for ePUB3 rendering. It is fully optimized for use on websites in browser-based cloud readers. One of the highlights of Readium JS is that it does not require any server-side infrastructure or browser plug.

Readium JS comprises two sub-projects, Readium Chrome Application and the Readium CloudReader. Both of these consist of three major elements:

  • Readium-js– is the core (similar to the C++ Core in the SDK) and offers all the basic services, manages the ePUB package, navigating and fetching resources, metadata, and more
  • Readium-js-viewer: It is primarily an application layer that manages the user-interface
  • Readium-shared-js: This is the same code as used in the SDK implementation

Suggested Read: Understanding Readium – Features, Architecture and Alternatives

Key Features of Readium

Among the key features of Readium include

  • Easy Portability

Available for both open source and proprietary apps, you can deploy or port Readium to a wide variety of platforms, including browsers,  desktop, mobile devices and native applications. 

  • Robust Compatibility

Readium is not just compatible with ePUB but also with various other standards such as WebPub. 

  • Compliance

Readium leverages regression testing to ensure both compliance and compatibility with the latest ePUB3 specifications. 

Other features of Readium.js include-

  • Fully optimized for use in native apps for multiple devices
  • Written in cross-platform C++ and JavaScript code, and is adequately designed to be combined with platform-specific glue code and a modern browser rendering engine 
  • Comes along with iOS and Android testing wrappers, known as launchers.


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Difference between ePUB.js and Readium?

While both these Javascript libraries are free to use commercially with many common features, it is pretty difficult to say which reader will best integrate with an unknown workflow without knowing the full scope of the project.

Some of the key differences between ePUB.js and Readium that you need to know about include-

Attention to Detail

The code in ePUB.js is well-written in a consistent style and is succinct without being confusing, which is great for readability. Readium JS, on the contrary, does not have the sophisticated style of the ePUB.js examples.


Unlike ePUB.js, Readium scores high on functionality. It has various tests (ePUB does not), closed issues, commits and active contributors (much more than ePUB). Further, support in the case of Readium does not seem like an issue because it is a sub-library of a larger, well-maintained application.


Another key difference between the two is usability for different projects. While ePUB.js would be an excellent choice for small projects due to its compact size and readability, Readium JS is more suitable for large projects with complex requirements.  

Put simply, ePUB.js is relatively good for getting something started off the ground quickly, whereas Readium.js, with its powerful testing suite and comparably robust development community, is ideal for the customer-facing project with a long life cycle.

Related Read: The Best eBook Platforms for the Post-Readium Era

Wondering how do you choose between the two then?

To help you decide the best among the two, make sure to rank each package based on the below criteria-


Quality includes multiple considerations such as stability, up-to-date dependencies, custom website, code complexity and tests.


Popularity here indicates how many times the package has been downloaded and reflects how useful it is for other users.


Maintenance typically ranks these packages based on the attention developers give them. 

Among the other key considerations, you need to take into account while choosing between ePUB.js and Readium include-

  • How easy is it to integrate either of these libraries into your current workflow?
  • Does the license suite of libraries suit your individual project needs?
  • How easy would it be to migrate to and from both these libraries?

To Wrap

A reading system, which could be a hardware device or an app, is one of the key requirements to read ePUB titles. While the readers can vary in their core features and functionality,  the main objective remains to offer a great reading experience to the users.

This article offers a detailed comparison and critical evaluation of two of the popular ePUB Readers- ReadiumJS Viewer and ePUB.js Reader- to give you an informed analysis of which one to go with for your specific publishing needs.

Contact our expert team now and get started!

For more information, write to us at contact@kitaboo.com

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Vishal Dani

Vishal Dani

Vishal is the Senior Vice President and Head - Cloud Platforms & Technology at HurixDigital. He leads the product development group and technology solutions. More posts by Vishal Dani