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# Best practices

## State management

We use React and Recoil for state management.

### Use `useRecoilState` to store state

We recommend that you create as many atoms as you need to store your state. 

Rule of thumb : It's better to be using too many atoms than trying to be too concise with props drilling.

```tsx
export const myAtomState = atom({
  key: 'myAtomState',
  default: 'default value',
});

export const MyComponent = () => {
  const [myAtom, setMyAtom] = useRecoilState(myAtomState);

  return (
    <div>
      <input
        value={myAtom}
        onChange={(e) => setMyAtom(e.target.value)}
      />
    </div>
  );
}
```

### Do not use `useRef` to store state

We do not recommend using `useRef` to store state. 

If you want to store state, you should use `useState` or `useRecoilState`.

We recommend seeing [how to manage re-renders](#managing-re-renders) if you feel like you need `useRef` to prevent some re-renders from happening.

## Managing re-renders

Re-renders can be hard to manage in React.

We provide you with some rules that we follow to avoid unnecessary re-renders.

Keep in mind that re-renders can **always** be avoided by understanding the cause of the re-render.

### Work at the root level

We made it easy for you to avoid re-renders in new features by taking care of eliminating them at the root level.

There's only one `useEffect` in the sidecar component `PageChangeEffect` that is holding all the logic that should be executed on a page change.

That way you know that there's only one place that can trigger a re-render.

### Always think twice before adding `useEffect` in your codebase

Re-renders are often caused by unnecessary `useEffect`.

You should think whether the useEffect is really needed, or if you can move the logic in a event handler function.

You'll find it generally easy to move the logic in a `handleClick` or `handleChange` function.

You can also find them in libraries like Apollo : `onCompleted`, `onError`, etc.

### Use a sibling component to extract useEffect or data fetching logic

If you feel like you need to add a `useEffect` in your root component, you should consider extracting it in a sidecar component.

The same can be applied for data fetching logic, with Apollo hooks.

```tsx
// ❌ Bad, will cause re-renders even if data is not changing, 
//    because useEffect needs to be re-evaluated
export const PageComponent = () => {
  const [data, setData] = useRecoilState(dataState);
  const [someDependency] = useRecoilState(someDependencyState);

  useEffect(() => {
    if(someDependency !== data) {
      setData(someDependency);
    }
  }, [someDependency]);

  return <div>{data}</div>;
};

export const App = () => (
  <RecoilRoot>
    <PageComponent />
  </RecoilRoot>
);
```

```tsx
// ✅ Good, will not cause re-renders if data is not changing, 
//   because useEffect is re-evaluated in another sibling component
export const PageComponent = () => {
  const [data, setData] = useRecoilState(dataState);

  return <div>{data}</div>;
};

export const PageData = () => {
  const [data, setData] = useRecoilState(dataState);
  const [someDependency] = useRecoilState(someDependencyState);

  useEffect(() => {
    if(someDependency !== data) {
      setData(someDependency);
    }
  }, [someDependency]);

  return <></>;
};

export const App = () => (
  <RecoilRoot>
    <PageData />
    <PageComponent />
  </RecoilRoot>
);
```

### Use recoil family states and recoil family selectors

Recoil family states and selectors are a great way to avoid re-renders.

They are especially useful when you need to store a list of items.

### You shouldn't use `React.memo(MyComponent)`

We do not recommend `React.memo()` usage because it does not solve the cause of the re-render, but instead breaks the re-render chain, which can lead to unexpected behavior and make the code really hard to refactor.

### Limit `useCallback` or `useMemo` usage

They are often not necessary and will make the code harder to read and maintain for a gain of performance that is unnoticeable.

## Console.logs

`console.log` statements are invaluable during development, offering real-time insights into variable values and code flow. However, leaving them in production code can lead to several issues: 

1. **Performance**: Excessive logging can affect the runtime performance, especially on client-side applications.
  
2. **Security**: Logging sensitive data can expose critical information to anyone who inspects the browser's console.

3. **Cleanliness**: Filling up the console with logs can obscure important warnings or errors that developers or tools need to see.

4. **Professionalism**: End users or clients checking the console and seeing a myriad of log statements might question the code's quality and polish.

## Naming

### Variable Naming

Variable names ought to precisely depict the purpose or function of the variable.

#### The issue with generic names
Generic names in programming are not ideal because they lack specificity, leading to ambiguity and reduced code readability. Such names fail to convey the variable or function's purpose, making it challenging for developers to understand the code's intent without deeper investigation. This can result in increased debugging time, higher susceptibility to errors, and difficulties in maintenance and collaboration. Descriptive naming, on the other hand, makes the code self-explanatory and easier to navigate, enhancing overall code quality and developer productivity.

```tsx
// ❌ Bad, uses a generic name that doesn't communicate its
//    purpose or content clearly
const [value, setValue] = useState('');
```

```tsx
// ✅ Good, uses a descriptive name
const [email, setEmail] = useState('');
```

#### Some words to avoid in variable names

 - dummy

### Event handlers

Event handler names should start with `handle`, `on` is a prefix used to name events in components props

```tsx
// ❌ Bad
const onEmailChange = (val: string) => {
  // ...
};
```

```tsx
// ✅ Good
const handleEmailChange = (val: string) => {
  // ...
};
```

## Optional Props

Avoid supplying the default value for an optional prop, as it generally doesn’t contribute significantly.

EXAMPLE

Assume, we have the `EmailField` component defined below

```tsx
type OwnProps = {
  value: string;
  disabled?: boolean;
};

const EmailField = ({ value, disabled = false }: OwnProps) => (
  <TextInput value={value} disabled={disabled} fullWidth />
);
```

USAGE

```tsx
// ❌ Bad, passing in the same value as the default value adds no value
const Form = () => <EmailField value="username@email.com" disabled={false} />;
```

```tsx
// ✅ Good, assumes the default value
const Form = () => <EmailField value="username@email.com" />;
```

## Component as props

Try as much as possible to pass uninstanciated components as props, so chilren can decide on their own of what props they need to pass.

The most common example for that is icon components : 

```tsx
const SomeParentComponent = () => <MyComponent Icon={MyIcon} />;

// In MyComponent
const MyComponent = ({ MyIcon }: { MyIcon: IconComponent }) => {
  const theme = useTheme();

  return (
    <div>
      <MyIcon size={theme.icon.size.md}>
    </div>
  )
};
```

For React to understand that the component is a component, you need to use PascalCase, to later instanciate it with `<MyIcon>`

```tsx

## Prop Drilling: Keep It Minimal

Prop drilling, in the React context, refers to the practice of passing state variables and their setters through multiple component layers, even if intermediary components don't use them. While sometimes necessary, excessive prop drilling can lead to:

1. **Decreased Readability**: Tracing where a prop originates or where it's utilized can become convoluted in a deeply nested component structure.
  
2. **Maintenance Challenges**: Changes in one component's prop structure might necessitate adjustments in several components, even if they don't directly use the prop.

3. **Reduced Component Reusability**: A component receiving numerous props solely for the purpose of passing them down becomes less general-purpose and harder to reuse in different contexts.

If you feel that you are using excessive prop drilling, see [state management best practices](/developer/frontend/best-practices#state-management)

## Imports

When importing, opt for the designated aliases rather than specifying complete or relative paths.

THE ALIASES

```js
{
  alias: {
    "~": path.resolve(__dirname, "src"),
    "@": path.resolve(__dirname, "src/modules"),
    "@testing": path.resolve(__dirname, "src/testing"),
  },
}
```

USAGE
```tsx
// ❌ Bad, specifies the entire relative path
import {
  CatalogDecorator
} from '../../../../../testing/decorators/CatalogDecorator';
import {
  ComponentDecorator
} from '../../../../../testing/decorators/ComponentDecorator';
```

```tsx
// ✅ Good, utilises the designated aliases
import { CatalogDecorator } from '~/testing/decorators/CatalogDecorator';
import { ComponentDecorator } from '~/testing/decorators/ComponentDecorator';=
```

## Breaking Changes

Prioritize thorough manual testing before proceeding to guarantee that modifications haven’t caused disruptions elsewhere, given that tests have not yet been extensively integrated.

