.. _OEP-11 Front End Technology Standards: OEP-11: Front End Technology Standards ###################################### +---------------+------------------------------------------------------+ | OEP | :ref:`OEP-11 `| +---------------+------------------------------------------------------+ | Title | Front End Technology Standards | +---------------+------------------------------------------------------+ | Last Modified | 2018-02-22 | +---------------+------------------------------------------------------+ | Author | Andy Armstrong , | | | George Babey | +---------------+------------------------------------------------------+ | Arbiter | Matt Drayer | +---------------+------------------------------------------------------+ | Status | Replaced | +---------------+------------------------------------------------------+ | Type | Best Practice | +---------------+------------------------------------------------------+ | Created | 2016-10-19 | +---------------+------------------------------------------------------+ .. warning:: This OEP has been replaced and may be out of date. For the most up-to-date information see :ref:`OEP-67 Standard Tools and Technologies`. Abstract ******** This document describes the technology standards for developing front end applications and components for Open edX. It covers the techniques and approaches that are currently recommended, as well as the technologies and libraries that should be used. Motivation ********** The rapid pace of development in front end tooling has created opportunities to greatly improve the quality of the Open edX user and developer experience. After an assessment of industry best practices, the edX Front End Working Group (FedX) has made a number of technology recommendations for libraries, frameworks and tooling to modernize the edX front end. Within this document, the phrase "front end" is used to mean any part of the platform that is shown to users. This encompasses views rendered in Python on the server, interactive interfaces written using JavaScript, and CSS styling. Specification ************* Technology Selection ==================== .. _Use React and Redux: #. **Use React** **Rationale**: React must be used for building new UIs, as it is widely adopted by the community and strikes a balance between flexibility and feature richness. When building in existing Django server-rendered pages, one can use the react_render helper method to bridge to React. This bridge provides an easy way to pass data into a React component from Django via props. For more information about react_render see `ReactRender`_. #. **Use Redux** For state management of complex client-side interactions, Redux must be used. This library was chosen because it sees strong use in the React community, but is also flexible enough to be used in situations where a hybrid React/Backbone architecture exists. #. **Use Jest and React-Testing-Library to test React components** We use `Jest`_ and `React-Testing-Library`_ to test React components. We are deprecating the `Enzyme`_ library. New tests must not use Enzyme, and any repositories planning to move to React 18 or newer need to replace Enzyme. #. **Target the latest standardized JavaScript version (ECMA-262)** **Rationale**: edX JavaScript should be written consistent with the latest ECMA-262 specification in order to ensure future support, the largest community and the availability of modern features. Currently, the ECMA-262 edition 6 (ES6) is the edition with the largest support and should be used. To support this syntax in older browsers, use `Babel`_. Babel may also be configured to add syntax extensions widely adopted by the community of our recommended framework (e.g., `JSX`_). **Exception**: Much of edX's existing front end code is written conformant to the edition of ECMA-262 released in 2009 (ES5). Files written in ES5 should be gradually converted to the newer standard as new development in those feature areas requires. **Note**: edX previously used CoffeeScript, but its use has now been deprecated. Community interest in TypeScript has also grown, but it and other languages that do not follow the ECMA-262 spec should not be used. #. **JavaScript code should follow the edX ESLint configuration** **Rationale**: In order to standardize and enforce Open edX's JavaScript coding style across multiple codebases, edX has published an ESLint configuration that provides an enforceable specification. The `edX ESLint Config`_ is made available as an npm package that can be installed into any Open edX package. **Exception**: The `edX ESLint Config for ES5`_ may be used only where ES5 is in use. Both configs may be used in the same codebase through the use of `ESLint configuration cascading`_. #. **JavaScript libraries should be installed via npm** **Rationale**: It is important that JavaScript libraries are kept up-to-date, and one key component is to make it as simple as possible to perform upgrades. Projects that use npm maintain all of their library requirements in a single `package.json` file, which can be easily changed as the versions change. #. **JavaScript projects should publish a package.lock file** **Rationale**: To keep dependencies up-to-date and builds consistent, JavaScript projects should allow patch and minor upgrades in their package.json file and commit a package-lock.json file. The package-lock.json file will keep a full list of dependencies and their versions, ensuring when built for deployments the version of libraries are consistent. This follows the same pattern used in edX Python code - see `OEP 18`_ for more information. For more information on package-lock files see `Package Lock`_. #. **Keep dependencies up to date by using Greenkeeper** **Rationale**: JavaScript dependencies are updated constantly and can be difficult to maintain over time. `Greenkeeper`_ makes this easier by automatically updating dependencies in a package.json file and verifying the tests still work. When possible, leverage Greenkeeper to ensure JavaScript software remains up to date. #. **JavaScript should be bundled using Webpack** **Rationale**: `Webpack`_ is the tool of choice for code optimization and bundling, as it is widely used throughout the industry, and because it seamlessly handles modern code bases as well as all of the older technologies used by edX, such as `AMD Modules`_. Webpack should be implemented to handle as much of the "asset pipeline" as possible, rather than passing this responsibility on to Django. #. **JavaScript dependencies should be managed with ES2015 Modules** **Rationale**: JavaScript module systems allow front end code to specify its dependencies and be grouped into bundles that minimize the assets needed to provide page functionality. The most prevalent module syntax is currently `ES2015 Modules`_, which should be adopted everywhere edX code is written to the ES2015 spec or later. **Exception**: Much of edX's existing (ES5) JavaScript uses the older `AMD Modules`_ syntax for modules. AMD Modules are interoperable with ES2015 Modules if Webpack is used for bundling, so AMD is an acceptable module definition if the code must remain ES5. #. **CSS should be generated using Sass** **Rationale**: Sass's SCSS syntax is an extension of CSS that adds power and elegance to the basic language. It makes the maintenance of large CSS files more manageable though the ability to use variables, mixins, imports and more. In particular, it makes theming possible with the ability to override variables that define colors, fonts etc. You can find out more about Sass in the official `Sass documentation`_. #. **API calls should be made with the edX Frontend Auth Client or Axios** **Rationale**: The `edX Frontend Auth Client`_ simplifies the process of talking to edX APIs by using Axios interceptors and handling JWT Cookie authentication. It also provides React components to handle private routes and should be used when possible. When making calls to non-edX APIs Axios should be used to provide a consistent API. The `fetch`_ API was considered but Axios was chosen for its more intuitive API, particularly when handling HTTP errors with rejected promises. #. **Server-side content should be rendered with Django Templates** **Rationale**: Although it is advised to use client side templating with React, see `Use React and Redux`_, when rendering on the server Django templates should be used. There are many template languages available for Django, but the simplest option is to use the built-in Django template engine. The Open edX codebase has a mixture of Django and Mako templates, but the former are easier to reason about because they don't support arbitrary code evaluation. **Exception**: Mako templates can continue to be used within edx-platform for consistency with the existing code base. This is because the base templates and theming support are all provided via Mako, so it is too much to expect a new feature to be implemented with a different framework. There is much desire to replace Mako within edx-platform so this exception may eventually be removed. #. **Codecov should be used to measure code covered by tests** **Rationale**: It is important to measure the amount of code covered by our automated test suites. By striving for a high level of test coverage, we can reduce the number of bugs that can only be found via manual testing. another added benefit comes when we include coverage runs in the CI process, as contributors are automatically reminded to include tests for any new code. The Open edX community has standardized around `Codecov`_ as a measurement tool. Decisions ********* .. note:: The decisions from this OEP have been moved to :ref:`OEP-67 Standard Tools and Technologies`. Change History ************** 2023-05-23 ========== * Mark Enzyme as deprecated * `Pull request #487 `_ .. Cross-references .. _AMD Modules: https://github.com/amdjs/amdjs-api/wiki/AMD .. _Babel: https://babeljs.io/ .. _Codecov: https://about.codecov.io/ .. _edX ESLint Config: https://github.com/edx/eslint-config-edx/tree/master/packages/eslint-config-edx .. _edX ESLint Config for ES5: https://github.com/edx/eslint-config-edx/tree/master/packages/eslint-config-edx-es5 .. _edx Frontend Auth Client: https://github.com/edx/frontend-auth .. _enzyme: https://airbnb.io/enzyme/ .. _enzyme-adapter-react-17: https://www.npmjs.com/package/@wojtekmaj/enzyme-adapter-react-17 .. _ESLint configuration cascading: https://eslint.org/docs/user-guide/configuring/configuration-files#cascading-and-hierarchy .. _ES2015 Modules: http://www.ecma-international.org/ecma-262/6.0/#sec-imports .. _ES2017: https://tc39.github.io/ecma262/ .. _Fetch: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API .. _Greenkeeper: https://greenkeeper.io/ .. _Jest: https://jestjs.io/ .. _JSX: https://facebook.github.io/react/docs/introducing-jsx.html .. _oep 18: https://docs.openedx.org/projects/openedx-proposals/en/latest/oep-0018-bp-python-dependencies.html .. _package lock: https://docs.npmjs.com/cli/v6/configuring-npm/package-locks .. _React: https://github.com/facebook/react .. _React at edX: https://openedx.atlassian.net/wiki/display/FEDX/React .. _React-Testing-Library: https://testing-library.com/docs/react-testing-library/intro .. _ReactRender: https://github.com/openedx/edx-platform/blob/4b38b1f750918ff83c02cff776681aabe44bd689/common/djangoapps/pipeline_mako/templates/static_content.html#L159-L167 .. _Sass documentation: http://sass-lang.com/ .. _Webpack: https://webpack.github.io/