# TypeScript convention
## Component
> **Public components** are considered all components exported from `@mui/material` or `@mui/lab`.
>
> **Internal components** are considered all components that are not exported from the packages, but only used in some public component.
### `Props Interface`
- export interface `{ComponentName}classes` from `{component}Classes.ts` and add comment for generating api docs (for internal components, may or may not expose classes but don't need comment)
- export interface `{ComponentName}Props`
- always export props interface (use `interface` over `type`) from the component file
Public component
```ts
// fooClasses.tsx
export interface FooClasses {
/** Styles applied to the root element. */
root: string;
/** Styles applied to the foo element. */
foo: string;
/** Styles applied to the root element if `disabled=true`. */
disabled: string;
}
const fooClasses: FooClasses = generateUtilityClasses('MuiFoo', ['root', 'foo', 'disabled']);
export default fooClasses;
```
```ts
// Foo.tsx
import { FooClasses } from './fooClasses';
export interface FooProps {
/**
* Override or extend the styles applied to the component.
*/
classes?: Partial;
// ...other props
/**
* The system prop that allows defining system overrides as well as additional CSS styles.
*/
sx?: SxProps;
}
```
internal component
```ts
// Bar.tsx
// if this internal component can accept classes as prop
export interface BarClasses {
root: string;
}
export interface BarProps {
classes?: Partial;
sx?: SxProps;
}
```
### `ClassKey`
- naming as `{ComponentName}ClassKey`
- export if `classes` exists in props interface using `keyof` from `{component}Classes.ts`
```ts
// fooClasses.ts
export interface FooClasses {
...
}
export type FooClassKey = keyof FooClasses;
// verify that FooClassKey is union of string literal
```
### `Classes generator & Utility`
- export if `classes` exists in props interface from the component file
- use `{Component}Classes` as type to preventing typo and missing classes
- use `Private` prefix for internal component
Public component
```ts
// fooClasses.ts
export function getFooUtilityClass(slot: string) {
return generateUtilityClass('MuiFoo', slot);
}
const useUtilityClasses = (ownerState: FooProps & { extraProp: boolean }) => {
// extraProp might be the key/value from react context that this component access
const { foo, disabled, classes } = ownerState;
const slots = {
root: ['root', foo && 'foo', disabled && 'disabled'],
};
return composeClasses(slots, getFooUtilityClass, classes);
};
```
internal component
```ts
// Bar.tsx
// in case that classes is not exposed.
// `classes` is used internally in this component
const classes = generateUtilityClasses('PrivateBar', ['root', 'bar']);
```
### `StyledComponent`
- naming using slot `{ComponentName}{Slot}`
- to extend interface of the styled component, pass argument to generic
public component
```ts
const FooRoot = styled(Typography, {
name: 'MuiFoo',
slot: 'Root',
overridesResolver: (props, styles) => styles.root,
})({
// styling
});
```
internal component
```ts
const BarRoot = styled(Typography)({
// styling
});
```
extends interface
```ts
const BarRoot = styled(Typography)<{
component?: React.ElementType;
ownerState: BarProps;
}>(({ theme, ownerState }) => ({
// styling
}));
// passing `component` to BarRoot is safe and we don't forget to pass ownerState
//
```
### `Component declaration`
- prefer `function Component() {}` over `React.FC`
- naming the render function in `React.forwardRef` (for devtools)
- `useThemeProps` is needed only for public component
- pass `ownerState` to StyledComponent for styling
public component
```ts
const Foo = React.forwardRef(function Foo(inProps, ref) => {
// pass args like this, otherwise will get error about theme at return section
const props = useThemeProps({
props: inProps,
name: 'MuiFoo',
});
const { children, className, ...other } = props
// ...implementation
const ownerState = { ...props, ...otherValue }
const classes = useUtilityClasses(ownerState);
return (
{children}
)
})
```
internal component
```ts
const classes = generateUtilityClasses('PrivateBar', ['selected']);
const BarRoot = styled('div')(({ theme }) => ({
[`&.${classes.selected}`]: {
color: theme.palette.text.primary,
},
}));
// if this component does not need React.forwardRef, don't use React.FC
const Bar = (props: BarProps) => {
const { className, selected, ...other } = props;
return ;
};
```