freeCodeCamp/docs/codebase-best-practices.md

Codebase Best Practices

Styling a component

We recommend styling components using our design style guide.

The colors are defined in variable.css, and the fonts are in fonts.css.

We are strongly opinionated about adding new variables/tokens to the colors. After careful research, the colors have been chosen to respect the freeCodeCamp brand identity, developer experience, and accessibility.

The !important keyword may be used to override values in some cases (e.g. accessibility concerns). You should add a comment describing the issue, so it doesn't get removed in future refactoring.

RTL support

We are striving to support right-to-left (RTL) layout in the codebase for languages that are read in this direction. For this, you need to be mindful of how to style components. Here are some quick rules of thumb to follow:

• Don't use float properties
  • Use Flexbox and Grid layouts instead, as they have RTL support already built-in, and those will be easier to maintain and review.
• Don't define the direction while using margin and padding: it may seem harmless to use padding-right and margin-left, but these directions aren't mirrored when the layout changes to RTL, and adding counter values for them in the RTL file makes maintaining the codebase harder.
  • Use logical properties for them: You can add the same spacing by using padding-inline-end and margin-inline-start, and you won't need to worry about RTL layout, as they follow where the line starts and ends, and you won't need to add any extra values in the RTL files, so people won't need to remember to change the same values in two files.
• Don't use !important in font-family: RTL layout uses different fonts compared to the LTR layout, when you add !important in the font-family property it affects the RTL layout too.

General JavaScript

In most cases, our linter will warn of any formatting which goes against this codebase's preferred practice.

It is encouraged to use functional components over class-based components.

Specific TypeScript

Migrating a JavaScript File to TypeScript

Retaining Git File History

Sometimes changing the file from <filename>.js to <filename>.ts (or .tsx) causes the original file to be deleted, and a new one created, and other times the filename just changes - in terms of Git. Ideally, we want the file history to be preserved.

The best bet at achieving this is to:

1. Rename the file
2. Commit with the flag --no-verify to prevent Husky from complaining about the lint errors
3. Refactor to TypeScript for migration, in a separate commit

Note

Editors like VSCode are still likely to show you the file has been deleted and a new one created. If you use the CLI to git add ., then VSCode will show the file as renamed in stage

Naming Conventions

Interfaces and Types

For the most part, it is encouraged to use interface declarations over type declarations.

React Component Props - suffix with Props

interface MyComponentProps {}
// type MyComponentProps = {};
const MyComponent = (props: MyComponentProps) => {};

React Stateful Components - suffix with State

interface MyComponentState {}
// type MyComponentState = {};
class MyComponent extends Component<MyComponentProps, MyComponentState> {}

Default - object name in PascalCase

interface MyObject {}
// type MyObject = {};
const myObject: MyObject = {};

Redux

Action Definitions

enum AppActionTypes = {
  actionFunction = 'actionFunction'
}

export const actionFunction = (
  arg: Arg
): ReducerPayload<AppActionTypes.actionFunction> => ({
  type: AppActionTypes.actionFunction,
  payload: arg
});

How to Reduce

// Base reducer action without payload
type ReducerBase<T> = { type: T };
// Logic for handling optional payloads
type ReducerPayload<T extends AppActionTypes> =
  T extends AppActionTypes.actionFunction
    ? ReducerBase<T> & {
        payload: AppState['property'];
      }
    : ReducerBase<T>;

// Switch reducer exported to Redux combineReducers
export const reducer = (
  state: AppState = initialState,
  action: ReducerPayload<AppActionTypes>
): AppState => {
  switch (action.type) {
    case AppActionTypes.actionFunction:
      return { ...state, property: action.payload };
    default:
      return state;
  }
};

How to Dispatch

Within a component, import the actions and selectors needed.

// Add type definition
interface MyComponentProps {
  actionFunction: typeof actionFunction;
}
// Connect to Redux store
const mapDispatchToProps = {
  actionFunction
};
// Example React Component connected to store
const MyComponent = ({ actionFunction }: MyComponentProps): JSX.Element => {
  const handleClick = () => {
    // Dispatch function
    actionFunction();
  };
  return <button onClick={handleClick}>freeCodeCamp is awesome!</button>;
};

export default connect(null, mapDispatchToProps)(MyComponent);

API

Testing

The api/ tests are split into two parts:

1. Unit tests
2. Integration tests

Unit Tests

Unit tests isolate a single function or component. The tests do not need mocking, but will require fixtures.

The unit tests are located in a new file adjacent to the file exporting that is being tested:

api/
├── src/
│   ├── utils.ts
│   ├── utils.test.ts

Integration Tests

Integration tests test the API as a whole. The tests will require mocking and should not require fixtures beyond the database seeding data and a method for authentication.

Typically, each integration test file will be directly related to a route. The integration tests are located in the api/tests/ directory:

api/
├── tests/
│   ├── settings.ts

Further Literature

• TypeScript Docs
• TypeScript with React CheatSheet