2.1. Introduction to XBlocks

This section introduces XBlocks.

2.1.1. Overview

The XBlock specification is a component architecture designed to make it easier to create new online educational experiences. XBlock was developed by edX, which has a focus in education, but the technology can be used in web applications that need to use multiple independent components and display those components on a single web page.

An XBlock developer does not need to download and run the entire edx-platform developer stack or to know anything about the technologies that edX uses to provide the XBlock runtime. Instead, XBlock developers writing with edX in mind can work from the xblock-sdk and deploy their work on any platform that is compatible with XBlocks.

In educational applications, XBlocks can be used to represent individual problems, web-formatted text and videos, interactive simulations and labs, or collaborative learning experiences. Furthermore, XBlocks are composable, allowing an XBlock developer to control the display of other XBlocks to compose lessons, sections, and entire courses.

2.1.2. XBlock API and Runtimes

Any web application can be an XBlock runtime by implementing the XBlock API. Note that the XBlock API is not a RESTful API. XBlock runtimes can compose web pages out of XBlocks that were developed by programmers who do not need to know anything about the other components that a web page might be using or displaying.

2.1.3. XBlocks and the edX Platform

The edX Platform is an XBlock runtime and edX currently provides most of the support for the development of the XBlock library and specification. Programmers who use the edx-platform devstack instead of the xblock-sdk to develop an XBlock should make sure that their XBlock is fully compliant with the XBlock specification before deploying to other XBlock runtimes. More specifically, XBlocks should package any services provided by edx-platform that a different XBlock compliant runtime might not provide.

The edX Platform currently has a large suite of XBlocks built into its primary repository that are available to course developers. Those XBlocks include HTML content, videos, and interactive problems. The edX Platform also includes many specialized XBlocks such as the Google Drive Files Tool and Introduction to Open Response Assessments. For more information, see XBlocks and the edX Platform.

2.1.4. XBlocks for Developers

Developers can select from functionality developed by the Open edX community by installing an XBlock on their instance of Open edX. Developers can integrate new or propriety functionality for use in XBlock runtimes by developing a new XBlock using the supported XBlock API.

XBlocks are like miniature web applications: they maintain state in a storage layer, render themselves through views, and process user actions through handlers. XBlocks differ from web applications in that they render only a small piece of a complete web page. Like HTML <div> tags, XBlocks can represent components as small as a paragraph of text, a video, or a multiple choice input field, or as large as a section, a chapter, or an entire course.

2.1.4.1. Prerequisites

This tutorial is for developers who are new to XBlock. To use this tutorial, you should have basic knowledge of the following technologies.

  • Python
  • JavaScript
  • HTML and CSS
  • Python virtualenv
  • Git

2.1.4.2. XBlock Resources

This tutorial is meant to guide developers through the process of creating an XBlock, and to explain the concepts and anatomy of XBlocks.

EdX provides the XBlock SDK to support the creation of new XBlocks. Developers should also see the EdX XBlock API Guide.

2.1.4.3. XBlock Independence and Interoperability

You must design your XBlock to meet two criteria.

  • The XBlock must be independent of other XBlocks. Course teams must be able to use the XBlock without using other XBlocks.
  • The XBlock must work together with other XBlocks. Course teams must be able to combine different XBlocks in flexible ways.