Debbie O'Brien

Posted on Jan 11, 2022 • Edited on Jan 24, 2022 • Originally published at debbie.codes

TypeScript and React Children

#react #typescript #tutorial

What happens when we pass in children in React? Children is a special prop that allows us to pass in any type of element. It could be a number, a string, a boolean, an array of elements or even another component. So how can we check the types?

Of course we could define it as any which is basically the same as just not having type checking which defeats the whole purpose of using Typescript.

There are a couple of types we could choose from:

JSX.Element

Children must be a single JSX element. Doesn't allow multiple children, or strings etc.

type ButtonProps = {
  children: JSX.Element
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export function Card() {
  return (
    <Button>
      <span>Click me</span>
    </Button>
  )
}

JSX.Element[]

Allows multiple JSX elements but no strings, numbers etc

type ButtonProps = {
  children: JSX.Element[]
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return (
    <Button>
      <span>click me</span>
      <i>svg icon</i>
    </Button>
  )
}

JSX.Element | JSX.Element[]

Allows single or multiple JSX elements but no strings, numbers etc

type ButtonProps = {
  children: JSX.Element | JSX.Element[]
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return (
    <Button>
      <span>click me</span>
    </Button>
  )
}
export default function Card2() {
  return (
    <Button>
      <span>click me</span>
      <i>svg icon</i>
    </Button>
  )
}

React.ReactChild

Allows one React element, string or number

type ButtonProps = {
  children: React.ReactChild
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return <Button>click me</Button>
}

React.ReactChild[]

Allows multiple React elements, strings or numbers

type ButtonProps = {
  children: React.ReactChild
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return (
    <Button>
      click me
      <i>svg icon</i>
    </Button>
  )
}

React.ReactChild | React.ReactChild[]

Allows single or multiple React elements, strings or numbers

type ButtonProps = {
  children: React.ReactChild
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return <Button>click me</Button>
}

export default function Card2() {
  return (
    <Button>
      click me
      <i>svg icon</i>
    </Button>
  )
}

React.ReactNode

Allows multiple children, strings, numbers, fragments, portals... We could use the above example but it is a little verbose and ReactNode covers a little more.

type ButtonProps = {
  children: React.ReactNode
}
const Button = ({ children }: ButtonProps) => <button>{children}</button>

export default function Card() {
  return (
    <Button>
      click me
      <i>svg icon</i>
    </Button>
  )
}

Conclusion

And that's it, you now have no excuses for adding type checking for your children.

Useful Links

Top comments (12)

Konstantin Komelin • Jan 11 '22

Hi Debbie,

Here is how I play with children:

import { FC, PropsWithChildren } from 'react';

type Props = {
  /* Other custom props */
}
const Component1:FC<PropsWithChildren<Props>> = ({children}) => {
  return (
    <>Component code</>
  )
}

Aniello Del Sorbo • Jan 12 '22

FC already accepts children, no need for PropsWithChildren.

If you don't want want children, you can use VFC.

dale tan • Apr 12 '22 • Edited

This is no longer true for FC with React 18. You must either use PropsWithChildren or explicitly add a children prop to your type definition.

Debbie O'Brien • Apr 12 '22

you're right. thanks for the comment.

Konstantin Komelin • Jan 12 '22

Thank you Aniello! Good to know.

Debbie O'Brien • Jan 12 '22

thanks guys, will play around with it

Renato Rodrigues • Jan 13 '22 • Edited

Nice article! There is only a small mistake on the last example where it reads children: React.ReactChild instead of children: React.ReactNode

Debbie O'Brien • Jan 24 '22

ooops. thanks just corrected it. nice catch

JamieBarlow • Aug 27

Hi Debbie, just came across this as it's missing from a number of courses I've used - a little surprising as React props are mentioned, but not the commonly used 'children' prop! Thanks for laying this out so clearly.