---
title: Style Guide
sidebar_position: 4
sidebar_custom_props:
  icon: TbPencil
---

This document includes the rules to follow when writing code.

The goal here is to have a consistent codebase, which is easy to read and easy to maintain. 

For this, it's better to be a bit more verbose than to be too concise.

Always keep in mind that people read code more often than they write it, specially on an open source project, where anyone can contribute.

There are a lot of rules that are not defined here, but that are automatically checked by linters.

## React

### Use functional components

Always use TSX functional components.

Do not use default `import` with `const`, because it's harder to read and harder to import with code completion.

```tsx
// ❌ Bad, harder to read, harder to import with code completion
const MyComponent = () => {
  return <div>Hello World</div>;
};

export default MyComponent;

// ✅ Good, easy to read, easy to import with code completion
export function MyComponent() {
  return <div>Hello World</div>;
};
```

### Props

Create the type of the props and call it `(ComponentName)Props` if there's no need to export it.

Use props destructuring.

```tsx
// ❌ Bad, no type
export const MyComponent = (props) => <div>Hello {props.name}</div>;

// ✅ Good, type
type MyComponentProps = {
  name: string;
};

export const MyComponent = ({ name }: MyComponentProps) => <div>Hello {name}</div>;
```

#### Refrain from using `React.FC` or `React.FunctionComponent` to define prop types

```tsx
/* ❌ - Bad, defines the component type annotations with `FC`
 *    - With `React.FC`, the component implicitly accepts a `children` prop
 *      even if it's not defined in the prop type. This might not always be
 *      desirable, especially if the component doesn't intend to render
 *      children.
 */
const EmailField: React.FC<{
  value: string;
}> = ({ value }) => <TextInput value={value} disabled fullWidth />;
```

```tsx
/* ✅ - Good, a separate type (OwnProps) is explicitly defined for the 
 *      component's props
 *    - This method doesn't automatically include the children prop. If
 *      you want to include it, you have to specify it in OwnProps.
 */ 
type EmailFieldProps = {
  value: string;
};

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

#### No Single Variable Prop Spreading in JSX Elements

Avoid using single variable prop spreading in JSX elements, like `{...props}`. This practice often results in code that is less readable and harder to maintain because it's unclear which props the component is receiving.

```tsx
/* ❌ - Bad, spreads a single variable prop into the underlying component
 */
const MyComponent = (props: OwnProps) => {
  return <OtherComponent {...props} />;
}
```

```tsx
/* ✅ - Good, Explicitly lists all props
 *    - Enhances readability and maintainability
 */ 
const MyComponent = ({ prop1, prop2, prop3 }: MyComponentProps) => {
  return <OtherComponent {...{ prop1, prop2, prop3 }} />;
};
```

Rationale:
- At a glance, it's clearer which props the code passes down, making it easier to understand and maintain.
- It helps to prevent tight coupling between components via their props.
- Linting tools make it easier to identify misspelled or unused props when you list props explicitly.

## JavaScript 

### Use nullish-coalescing operator `??`

```tsx
// ❌ Bad, can return 'default' even if value is 0 or ''
const value = process.env.MY_VALUE || 'default';

// ✅ Good, will return 'default' only if value is null or undefined
const value = process.env.MY_VALUE ?? 'default';
```

### Use optional chaining `?.`

```tsx
// ❌ Bad 
onClick && onClick();

// ✅ Good
onClick?.();
```

## TypeScript

### Use `type` instead of `interface`

Always use `type` instead of `interface`, because they almost always overlap, and `type` is more flexible.

```tsx
// ❌ Bad
interface MyInterface {
  name: string;
}

// ✅ Good
type MyType = {
  name: string;
};
```

### Use string literals instead of enums

[String literals](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#literal-types) are the go-to way to handle enum-like values in TypeScript. They are easier to extend with Pick and Omit, and offer a better developer experience, specially with code completion.

You can see why TypeScript recommends avoiding enums [here](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#enums). 

```tsx
// ❌ Bad, utilizes an enum
enum Color {
  Red = "red",
  Green = "green",
  Blue = "blue",
}

let color = Color.Red;
```

```tsx
// ✅ Good, utilizes a string literal
let color: "red" | "green" | "blue" = "red";
```

#### GraphQL and internal libraries

You should use enums that GraphQL codegen generates.

It's also better to use an enum when using an internal library, so the internal library doesn't have to expose a string literal type that is not related to the internal API.

Example: 

```TSX
const {
  setHotkeyScopeAndMemorizePreviousScope,
  goBackToPreviousHotkeyScope,
} = usePreviousHotkeyScope();

setHotkeyScopeAndMemorizePreviousScope(
  RelationPickerHotkeyScope.RelationPicker,
);
```

## Styling

### Use StyledComponents

Style the components with [styled-components](https://emotion.sh/docs/styled).

```tsx
// ❌ Bad
<div className="my-class">Hello World</div>
```

```tsx
// ✅ Good
const StyledTitle = styled.div`
  color: red;
`;
```

Prefix styled components with "Styled" to differentiate them from "real" components.

```tsx
// ❌ Bad
const Title = styled.div`
  color: red;
`;
```

```tsx
// ✅ Good
const StyledTitle = styled.div`
  color: red;
`;
```

### Theming

Utilizing the theme for the majority of component styling is the preferred approach.

#### Units of measurement

Avoid using `px` or `rem` values directly within the styled components. The necessary values are generally already defined in the theme, so it’s recommended to make use of the theme for these purposes.

#### Colors

Refrain from introducing new colors; instead, use the existing palette from the theme. Should there be a situation where the palette does not align, please leave a comment so that the team can rectify it.


```tsx
// ❌ Bad, directly specifies style values without utilizing the theme
const StyledButton = styled.button`
  color: #333333;
  font-size: 1rem;
  font-weight: 400;
  margin-left: 4px;
  border-radius: 50px;
`;
```

```tsx
// ✅ Good, utilizes the theme
const StyledButton = styled.button`
  color: ${({ theme }) => theme.font.color.primary};
  font-size: ${({ theme }) => theme.font.size.md};
  font-weight: ${({ theme }) => theme.font.weight.regular};
  margin-left: ${({ theme }) => theme.spacing(1)};
  border-radius:  ${({ theme }) => theme.border.rounded};
`;
```
## Enforcing No-Type Imports

Avoid type imports. To enforce this standard, an ESLint rule checks for and reports any type imports. This helps maintain consistency and readability in the TypeScript code. 

```tsx
// ❌ Bad
import { type Meta, type StoryObj } from '@storybook/react';

// ❌ Bad
import type { Meta, StoryObj } from '@storybook/react';

// ✅ Good
import { Meta, StoryObj } from '@storybook/react';
```

### Why No-Type Imports

- **Consistency**: By avoiding type imports and using a single approach for both type and value imports, the codebase remains consistent in its module import style.

- **Readability**: No-type imports improve code readability by making it clear when you're importing values or types. This reduces ambiguity and makes it easier to understand the purpose of imported symbols.

- **Maintainability**: It enhances codebase maintainability because developers can identify and locate type-only imports when reviewing or modifying code.

### ESLint Rule

An ESLint rule, `@typescript-eslint/consistent-type-imports`, enforces the no-type import standard. This rule will generate errors or warnings for any type import violations.

Please note that this rule specifically addresses rare edge cases where unintentional type imports occur. TypeScript itself discourages this practice, as mentioned in the [TypeScript 3.8 release notes](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-8.html). In most situations, you should not need to use type-only imports.

To ensure your code complies with this rule, make sure to run ESLint as part of your development workflow.
