cosmos-explorer/CODING_GUIDELINES.md

Coding Guidelines and Recommendations

Cosmos Explorer has been under constant development for over 5 years. As a result, there are many different patterns and practices in the codebase. This document serves as a guide to how we write code and helps avoid propagating practices which are no longer preferred. Each requirement in this document is labeled and color-coded to show the relative importance. In order from highest to lowest importance:

✅ DO this. If you feel you need an exception, engage with the project owners prior to implementation.

⛔️ DO NOT do this. If you feel you need an exception, engage with the project owners prior to implementation.

☑️ YOU SHOULD strongly consider this but it is not a requirement. If not following this advice, please comment code with why and proactively begin a discussion as part of the PR process.

⚠️ YOU SHOULD NOT strongly consider not doing this. If not following this advice, please comment code with why and proactively begin a discussion as part of the PR process.

💭 YOU MAY consider this advice if appropriate to your situation. Other team members may comment on this as part of PR review, but there is no need to be proactive.

Development Environment

☑️ YOU SHOULD

• Use VSCode and install the following extensions. This setup will catch most linting/formatting/type errors as you develop:
  • Prettier
  • ESLint

💭 YOU MAY

• Use the GitHub CLI. It has helpful workflows for submitting PRs as well as for checking out other team member's PRs.
• Use Windows, Linux (including WSL), or OSX. We have team members developing on all three environments.

✅ DO

• Maintain cross-platform compatibility when modifying any engineering or build systems

Code Formatting

✅ DO

• Use Prettier to format your code
  • This will occur automatically if using the recommended editor setup
  • npm run format will also format code

Linting

✅ DO

• Use ESLint to check for code errors.
  • This will occur automatically if using the recommended editor setup
  • npm run lint will also check for linting errors

💭 YOU MAY

• Consider adding new lint rules.
  • If you find yourself performing "nits" as part of PR review, consider adding a lint rule that will automatically catch the error in the future

⚠️ YOU SHOULD NOT

• Disable lint rules
  • Lint rules exist as guidance and to catch common mistakes
  • You will find places we disable specific lint rules however it should be exceptional.
  • If a rule does need to be disabled, prefer disabling a specific line instead of the entire file.

⛔️ DO NOT

• Add TSLint rules
  • TSLint has been deprecated and is on track to be removed
  • Always prefer ESLint rules

UI Components

☑️ YOU SHOULD

• Write new components using React. We are actively migrating Cosmos Explorer off of Knockout.
• Use Fluent components.
  • Fluent components are designed to be highly accessible and composable
  • Using Fluent allows us to build upon the work of the Fluent team and leads to a lower total cost of ownership for UI code

React

☑️ YOU SHOULD

• Use pure functional components when no state is required

💭 YOU MAY

• Use functional (hooks) or class components
  • The project contains examples of both
  • Neither is strongly preferred at this time

⛔️ DO NOT

• Use inheritance for sharing component behavior.
  • React documentation covers this topic in detail https://reactjs.org/docs/composition-vs-inheritance.html
• Suffix your file or component name with "Component"
  • Even though the code has examples of it, we are ending the practice.

Libraries

⚠️ YOU SHOULD NOT

• Add new libraries to package.json.
  • Adding libraries may bring in code that explodes the bundled size or attempts to run NodeJS code in the browser
  • Consult with project owners for help with library selection if one is needed

⛔️ DO NOT

• Use underscore.js
  • Much of this library is now native to JS and will be automatically transpiled
• Use jQuery
  • Much of this library is not native to the DOM.
  • We are planning to remove it

Testing

⛔️ DO NOT

• Decrease test coverage
  • Unit/Functional test coverage is checked as part of the CI process

Unit Tests

✅ DO

• Write unit tests for non-UI and utility code.
• Write your tests using Jest

☑️ YOU SHOULD

• Abstract non-UI and utility code so it can run either the NodeJS or Browser environment

Functional(Component) Tests

✅ DO

• Write tests for UI components
• Write your tests using Jest
• Use either Enzyme or React Testing Library to perform component tests.

Mocking

✅ DO

• Use Jest's built-in mocking helpers

☑️ YOU SHOULD

• Write code that does not require mocking
• Build components that do not require mocking extremely large or difficult to mock objects (like Explorer.ts). Pass only what you need.

⛔️ DO NOT

• Use sinon.js for mocking
  • Sinon has been deprecated and planned for removal

End to End Tests

✅ DO

• Use Playwright and Jest
• Write or modify an existing E2E test that covers the primary use case of any major feature.
  • Use caution. Do not try to cover every case. End to End tests can be slow and brittle.

☑️ YOU SHOULD

• Write tests that use accessible attributes to perform actions. Role, Title, Label, etc
  • More information https://testing-library.com/docs/queries/about#priority

⚠️ YOU SHOULD NOT

• Add test specfic data-* attributes to dom elements
  • This is a common current practice, but one we would like to avoid in the future
  • End to end tests need to use semantic HTML and accesible attributes to be truely end to end
  • No user or screen reader actually navigates an app using data-* attributes
• Add arbitrary time delays to wait for page to render or element to be ready.
  • All the time delays add up and slow down testing.
  • Prefer using the framework's "wait for..." functionality.

Migrating Knockout to React

✅ DO

• Consult other team members before beginning migration work. There is a significant amount of flux in patterns we are using and it is important we do not propagate incorrect patterns.
• Start by converting HTML to JSX: https://magic.reactjs.net/htmltojsx.htm. Add functionality as a second step.

☑️ YOU SHOULD

• Write React components that require no dependency on Knockout or observables to trigger rendering.

Browser Support

✅ DO

• Support all browsers supported by the Azure Portal
• Support IE11
  • In practice, this should not need to be considered as part of a normal development workflow
  • Polyfills and transpilation are already provided by our engineering systems.
  • This requirement will be removed on March 30th, 2021 when Azure drops IE11 support.