React + TypeScript usage of className prop

Question

What is the correct way to type and use the className prop in a custom component? I used to be able to do this:

class MyComponent extends React.Component<MyProps, {}> {
  ...
}

and then use my component via:

<MyComponent className="my-class" />

Note that I would not define className in MyProps, though React was previously typed to support this usage.

Now, I am now seeing this type error:

Property 'className' does not exist on type 'IntrinsicAttributes & 
IntrinsicClassAttributes<Component<{}, ComponentState>> & Readonly<{ 
childr...'

What is the correct way to define / type my component that will allow me to use className when using my component?

Answer 1

You can use the HTMLAttributes type, for example:

class MyComponent extends React.Component<MyProps & React.HTMLAttributes<HTMLDivElement>, {}> {
    render() {
        return <div className={ this.props.className }>My Div</div>
    }
}

That way you can pass any of the properties that a html element might need.

If you only need the className property then you can do this:

class MyComponent extends React.Component<MyProps & { className: string }, {}> {
    render() {
        return <div className={ this.props.className }>My Div</div>
    }
}

Or simply add it to your MyProps type.

Answer 2

For someone who are looking solution for functional components, as I was.

type Props = {
  className?: string
}

const MyComponent: React.FC<Props> = (props) => (
  <div className={props.className}>{props.children}</div>
)

export default MyComponent

or if you want to declare interface separately:

interface OnlyClassNameInterface extends React.FC<{className: string}> {}

const MyComponent: OnlyClassNameInterface = (props) => (
  <div className={props.className}>{props.children}</div>
)

export default MyComponent

and you can move interface to another file

import React from 'react'

type MixProps<P> = P & {className?: string}

export interface OnlyClassNameInterface<P = {}> extends React.FC<MixProps<P> {}

Answer 3

add a react-native-class-name.polyfill.d.ts

import 'react-native';
// polyfill className prop for react-native Components
declare module 'react-native' {
  interface TextProps {
    className?: string;
  }
  interface PressableProps {
    className?: string;
  }
  interface TextInputProps {
    className?: string;
  }

  interface ViewProps {
    className?: string;
  }
  interface InputAccessoryViewProps {
    className?: string;
  }

  interface ImagePropsBase {
    className?: string;
  }

  interface TouchableWithoutFeedbackProps {
    className?: string;
  }
  // others StyleProp<?> in node_modules/@types/react-native extends up show, should not define again.
}