freeCodeCamp/docs/codebase-best-practices.md

# Codebase Best Practices

## General JavaScript

In most cases, our [linter](how-to-setup-freecodecamp-locally?id=follow-these-steps-to-get-your-development-environment-ready) 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`

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

React Stateful Components - suffix with `State`

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

Default - object name in PascalCase

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

<!-- #### Redux Actions -->

<!-- TODO: Once refactored to TS, showcase naming convention for Reducers/Actions and how to type dispatch funcs -->

## Redux

### Action Definitions

```typescript
enum AppActionTypes = {
  actionFunction = 'actionFunction'
}

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

### How to Reduce

```typescript
// 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.

```tsx
// 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);
```

<!-- ### Redux Types File -->
<!-- The types associated with the Redux store state are located in `client/src/redux/types.ts`... -->

## Further Literature

- [TypeScript Docs](https://www.typescriptlang.org/docs/)
- [TypeScript with React CheatSheet](https://github.com/typescript-cheatsheets/react#readme)