Perseus

Perseus is Khan Academy's new exercise question editor and renderer. It allows you to create and display interactive questions.

Live demo

Our test page isn't much yet, but you can check out a live demo of it here!

Getting Started

To get the dev server running locally, try make server PORT=9000 which will run the local perseus server on localhost:9000. Then visit http://localhost:9000/.

To package perseus for distribution, run make build and to package a debug-friendly build, run make debug.

Both the build and the server make targets will run npm install but you can also run it yourself to install all node dependencies.

External dependencies

Perseus makes a couple of assumptions about the environment that it's loaded into. Specifically, it expects the following libraries to be available on the global window object. (If any of them change in a backwards-incompatible way, you'll likely need to bump the Perseus major version -- see the "Versioning" section below.)

• React
• _ (underscore)
• jquery
• aphrodite
• classnames

(See externalVals in webpack.config.js)

Also, the following global variables are used, if present:

• Khan (warnMathJaxError & warnFont)
• icu (a subset of the localeplanet api is depended on, as covered by icu-slim.js from our fork of localeplanet)
• MathQuill
• Exercises
• KhanUtil (localeToFixed & debugLog)
• KaTeX

(See src/perseus-env.js and src/demo-perseus.js)

Versioning

Perseus uses two types of version numbers: the version of the itemData/content that can be sent to ItemRenderer/Renderer, and the version of the api exposed through the ItemRenderer/Renderer apiOptions prop. These are set in src/version.json.

itemData versioning

Item data versioning has two subtypes of versions: a global itemDataVersion for the itemData/content format sent to ItemRenderer/Renderer, and per-widget version numbers for the options sent to each widget. All of these version numbers exist both in perseus.js and in the itemData saved to the datastore by the Perseus editor.

Each of these versions consists of a major and minor version number. A perseus version can render an itemData version iff its global itemDataVersion and each of its widget versions are greater than or equal to those sent to perseus as itemData. A major version increase will happen when the saving format of this itemData has changed. Perseus clients should not need to care about this distinction, but it is important to Perseus' implementation of backwards-compatibility.

apiOptions versioning

The version of the apiOptions prop sent to ItemRenderer or Renderer is stored on Perseus.apiVersion. A minor version increase indicates an optional additional parameter to this interface. A major version increase indicates a not-backwards-compatible change to this API. A perseus client should rely on a specific major version of perseus, and should be able to use any future minor version increase without changes, but not necessarily previous minor versions. For example, if a client begins using version 1.2, Perseus api versions 1.3 or 1.4 will work transparently, but Perseus api versions 1.0, 1.1, 2.0, or 2.2 will not work.

Mobile versioning

The KA mobile apps are also clients of Perseus, and the way that Perseus is integrated into the apps requires that we enforce some additional versioning constraints. For specifics, check out the Forge page.

Contributing

See CONTRIBUTING.md for a walkthrough of how some of the Perseus code works and how to extend it.

License

MIT License