@lyvly/eslint-config v3.0.0

Lyvly Javascript Style Guide

How to install

# install the package
yarn add -D @lyvly/eslint-config

# install peer deps
yarn add -D babel-eslint@10.1 eslint-plugin-import@2.2 eslint-plugin-jest@23.8

# if you're using react
yarn add -D eslint-plugin-jsx-a11y@6.2 eslint-plugin-react@7.18 eslint-plugin-react-hooks@2

# in your eslint config
module.exports = {
  extends: ['@lyvly'],
  settings: {
    'import/resolver': {
      'babel-module': {},
    },
  },
};

Rules

Fork of https://github.com/airbnb/javascript

An approach to JavaScript that mostly follows AirBnB's guidelines with some minor tweaks

Backend

1. Exporting functions

• Use only named exports.

    // Preferred 🚀
    // ------------
    export const myFunction = () => {}
    
    // Avoid 👎
    // --------
    const myFunction = () => {}
    export default myFunction
    
    // Avoid 👎
    // --------
    export default () => {}

• Relatedly: do not use index files. Always import directly from the relevant file.

Why?

• This ensures consistent naming across the codebase.
  • In comparison, if you use a default export then you can rename it on import.
• Also: it helps us write self-contained tests (see rule 4). You can use jest.mock on the entire module, and then modify its implementation on a test-by-test basis:

    // Preferred 🚀
    // ------------
    import { myFunction } from './myFunction'
    
    jest.mock('./myFunction')
    
    describe('myModule', () => {
    	it('does one thing', () => {
    		myFunction.mockReturnValue('foo')
    	})
    
    	it('does another thing', () => {
    		myFunction.mockReturnValue('bar')
    	})
    })

2. Writing related functions

• If you are writing several related functions (e.g. crud operations for an entity), put them in the same file.
• When you import those functions, use wildcard syntax:

    // Preferred 🚀
    // ------------
    import * as memberDomain from './memberDomain'
    
    memberDomain.create()
    memberDomain.update()
    
    // Avoid 👎
    // --------
    import { create, update } from './memberDomain'
    
    create()
    update()

• When naming functions, don't repeat yourself:

    // Preferred 🚀
    // ------------
    memberDomain.create()
    memberDomain.update()
    
    // Avoid 👎
    memberDomain.createMember()
    memberDomain.updateMember()

• If your test file is getting large, don't be afraid to have several smaller test files for one module.

Why?

• This helps distinguish between several similarly named functions. For example, we can tell that something like memberDomain.create will write to the database, while memberApi.create will call an api.

3. Writing individual helper functions

• If you are writing an individual helper function which isn't obviously related to other functions (e.g. parseResponse or authenticate), put it in its own file.
• However, these should still be exported using a named export, as per rule 1.
• Import these directly, instead of using wildcard syntax which is unnecessarily clunky:

    // Preferred 🚀
    // ------------
    import { parseResponse } from './parseResponse'
    parseResponse()
    
    // Avoid 👎
    // --------
    import * as parseResponse from './parseResponse'
    parseResponse.parseResponse()

• Keep these files as close as possible to the things that use them. This means we can easily move/delete the things that use them, without having to move/copy helper functions from lots of different places.
  • Relatedly: do not create a global utils folder except for truly global things.

4. Tests should be self-contained

• Each test should contain all of the code required to understand that test.

    // Preferred 🚀
    // ------------
    it('finds an existing member', () => {
    	// Seed the database
    	memberDomain.create({ firstName: 'Homer', lastName: 'Simpson' })
    
    	const member = memberDomain.find({ firstName: 'Homer' })
    	expect(member).toEqual({ firstName: 'Homer', lastName: 'Simpson' })
    })
    
    it('updates an existing member', () => {
    	// Seed the database
    	memberDomain.create({ firstName: 'Homer', lastName: 'Simpson' })
    
    	const member = memberDomain.update({ firstName: 'Homer' }, { firstName: 'Marge' })
    	expect(member).toEqual({ firstName: 'Marge', lastName: 'Simpson' })
    })
    
    
    // Avoid 👎
    // --------
    beforeEach(() => {
    	// Seed the database
    	memberDomain.create({ firstName: 'Homer', lastName: 'Simpson' })
    })
    
    it('finds an existing member', () => {
    	const member = memberDomain.find({ firstName: 'Homer' })
    	expect(member).toEqual({ firstName: 'Homer', lastName: 'Simpson' })
    })
    
    it('updates an existing member', () => {
    	const member = memberDomain.update({ firstName: 'Homer' }, { firstName: 'Marge' })
    	expect(member).toEqual({ firstName: 'Marge', lastName: 'Simpson' })
    })

• Additionally, tests should be independent. So you should make sure that each test is operating on a different entity in the database, or that you're wiping the data between each test.

Why?

• If a test breaks, then you can quickly understand what that test is doing — and hence what might be wrong.

Related to this:

5. Don't be afraid of duplicating code

Why?

• In a microservices / serverless world, we're duplicating a lot of code anyway.
• When modules and folders are self-contained, it's easier to move or delete them. It's way more painful if those modules / folders depend on shared helper functions which are used by other modules / folders.

Rules of Thumb

• Things that are generally good to duplicate: schemas, business logic.
• Things that are generally bad to duplicate: things which should be uniform, like logging.

Frontend

The rules are the same as for the backend, except for the following exceptions:

1. Use default exports for React components

Why?

• This is common practice for React components.
• It also helps when testing components wrapped by higher-order components. If you use a default export for the wrapped component, and a named export for the base component, you can use the latter in your tests:

    // If your React component looks like this:
    export const Title = () => {
    	return (
    		<p>Lyvly</p>
    	)
    }
    
    export default compose(
    	inject('listingStore'),
    	observer
    )(Title)
    
    // Then your test can use the named export:
    import { Title } from './Title'
    
    describe('<Title />', () => {
    	it('matches snapshot', () => {
    		// No mocking of MobX required!
    		expect(Title).toMatchSnapshot()
    	})
    })

2. Use index files for React components

Why?

• Unlike the backend, there are several files associated with a component. Using an index file means that we can use a neater import whenever we use that component:

    // For a file structure that looks like this:
    // Title/
    // -- Title.js
    // -- Title.props.js
    // -- Title.style.js
    // -- Title.storybook.js
    // -- index.js
    
    // If we have an index file like this:
    import Title from './Title'
    export default Title
    
    // We can import the Title component like this:
    import Title from '@components/Title'
    
    // Rather than like this:
    import Title from '@components/Title/Title'