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Contribution guidelines

  1. Code style
  2. Testing
  3. Tools we use
  4. Component patterns
  5. Writing Documentation
  6. Deployment
  7. Glossary

Code Style

We use the React configuration from GitHub's eslint plugin to lint our JavaScript. To check your work before pushing, run:

npm run lint

Or, you can use npx to run eslint on one or more specific files:

# lint the component and the tests in src/__tests__
npx eslint src/**/MyComponent.js

Protip: The eslint --fix flag can automatically fix most linting errors, such as those involving whitespace or incorrect ordering of object keys and imports. You can fix those issues across the entire project with:

npm run lint -- --fix

Protip: npm run lint -- --quiet (or npx eslint --quiet ...) will suppress warnings so that you can focus on fixing errors.


We test our components with Jest and react-test-renderer. You can run the tests locally with npm test (or npm t). To run the tests as you work, run Jest in watch mode with:

npm t -- --watch

See src/__tests__/example.js for examples of ways that we test our components.

Code coverage

A code coverage report is included in the npm test output, and test coverage data is generated in the coverage/ directory.

Tools we use

  1. We use styled-components to style our components.
  2. We use style functions from styled-system whenever possible, and styled-systems' style() function to create new ones.

Component patterns

With a couple of exceptions, all components should be created with the styled function from [styled-components] and should have the appropriate groups of system props attached.

Default values for system props can be set in Component.defaultProps.

Prop Types from system props such as COMMON or TYPOGRAPHY as well as styled-system functions can be spread in the component's prop types declaration (see example below).

⚠️ Make sure to always set the default theme prop to our theme! This allows consumers of our components to access our theme values without a ThemeProvider.

import {TYPOGRAPHY, COMMON} from './constants'
import theme from './theme'

const Component = styled.div`

Component.defaultProps = {
  theme, // make sure to always set the default theme!
  m: 0,
  fontSize: 5,

Component.propTypes = {

export default Component

Categories of system props are exported from src/constants.js:

  • COMMON includes color and spacing (margin and padding) props
  • TYPOGRAPHY includes font family, font weight, and line-height props
  • POSITION includes positioning props
  • FLEX_CONTAINER includes flexbox props for containers
  • FLEX_ITEM includes flexbox props for items in a flex container

Writing documentation

We use Next.js and MDX Docs to power our documentation site at

To add a new component to our documentation site:

  1. Create a new file with the .md extension for your component in pages/components/docs.
  2. Copy & paste the template from & replace placeholder brackets with relevant information.
  3. Add the new file to the index.js in pages/components/docs


We deploy the Primer Components site using Now. Install the Now CLI and log in with:

npm i -g now
now login

Once you're logged in, sync your local git repo with the master branch and run:


This will create a new deployment and alias it to its production URL,

Path aliasing

This site is served as a subdirectory of using a path alias configured in that repo's rules.json. If you change the production deployment URL for this app, you will also need to change it there and re-deploy that app; otherwise, Now will automatically route requests from to the new deployment whenever you alias this one to


System props

System props are style functions that provide one or more props, and can be passed directly the return value of [styled-components]'s styled() function:

import {styled} from 'styled-components'
import {space} from 'styled-system'
const SpaceDiv = styled.div`

System props come with propTypes that can be mixed into your own with ES6 spread syntax:

SpaceDiv.propTypes = {
  stellar: PropTypes.bool,
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