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Juhana Jauhiainen
Juhana Jauhiainen

Posted on • Originally published at juhanajauhiainen.com

Should you use React.FC to type your components?

TLDR: No. You should probably not.

const Dialog: React.FC = ({children}) => {
    return (
        ...
    )
}
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The consensus in the React community now seems to be that, you should avoid using React.FC because it causes the component to implicitly take children. This means the component will accept children, even if they're not supposed to.

Let's take a look at the pros and cons of React.FC.

Pros of React.FC

Excplicit return type

In addition to the children prop, React.FC declares an explicit return type for the component. The return type is ReactElement | null; and we will get a type error if we try to return something else from the component.

const Header: React.FC = () => {
    return "test";
  )
}

/*
  Type '() => string' is not assignable to type 'FC<{}>'.
  Type 'string' is not assignable to type 'ReactElement<any, any> | null'.ts(2322)
*/

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Component static properties

Here's the full definition of React.FunctionComponent which React.FC is a shorthand for.

interface FunctionComponent<P = {}> {
  (props: PropsWithChildren<P>, context?: any): ReactElement<any, any> | null;
  propTypes?: WeakValidationMap<P> | undefined;
  contextTypes?: ValidationMap<any> | undefined;
  defaultProps?: Partial<P> | undefined;
  displayName?: string | undefined;
}
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In addition to the function signature, React.FC provides type checking for some static properties. propTypes and defaultProps define the prop types based on the generic type P. These provide type validation for props you pass to the component and default prop values you can define with Component.defaultProps = {}.

contextTypes and displayName are less useful in most situations.
contextTypes is related to a legacy Context.

displayName is used in debug messages.

Cons

Implicit children

The biggest downside to using React.FC is that it causes the component to implicitly take children. This means all components defined using React.FC will happily accept children, even when they're not supposed to.

const Icon: React.FC = <span className="icon">...</span>;

const OhNoh = <Icon>This should be a error</Icon>;
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This won't be a runtime error, but TypeScript would catch this error if React.FC had not been used.

Component as namespace

React.FC also doesn't accept generics (GeneriComponent<T>) and makes using the "component as namespace" pattern awkward to type.

<Dialog>
  <Dialog.Content></Dialog.Content>
</Dialog>;

const Dialog: React.FC<DialogProps> & { Content: React.FC<ContentProps> } = (
  props
) => {
  /*..*/
};
Dialog.Content = (props) => {
  /*...*/
};

//vs

const Dialog = (props: DialogProps) => {
  /*...*/
};
Dialog.Content = (props: ContentProps) => {
  /*..*/
};
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Alternatives

Explicit props and return type

If you want to have the benefits of explicit return types, you can use JSX.Element to explicitly type the return value of your components. children should be typed with React.ReactNode since it accepts all valid children values

interface Props {
    children: React.ReactNode;
}

const Header = ({children}: Props): JSX.Element => {
    return "test";
  )
}

/*
  Type 'string' is not assignable to type 'Element'.ts(2322)
*/

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Explicit props but implicit return type

This is my preferred way of typing React components. I find the implicit return type is usually not a problem and haven't had any bugs where a component is returning something it's not supposed to.

interface Props {
    children: React.ReactNode;
}

function Header({children}: Props) {
    ...
}

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In my opinion, this is a pretty clear and clean way of typing React components. What this way loses in typesafe, it gains in readability. I also prefer using named functions because I think they are more readable than the array functions.

Photo by Ash Edmonds on Unsplash

Discussion (1)

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lukeshiru profile image
Luke Shiru

You can use React.VFC if you don't want to use children.