Hoc example that supports default props of wrapped component

[ferdaber]

Cc @brieb

[ferdaber]

working example:

import React from 'react'

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>

export interface WithThemeProps {
  theme: {}
}

interface AddlProps {
  foo: string
}

function withTheme<C extends React.JSXElementConstructor<React.ComponentProps<C> & WithThemeProps>>(
  Component: C
) {
  type OuterProps = JSX.LibraryManagedAttributes<
    C,
    Omit<React.ComponentProps<C>, keyof WithThemeProps>
  > &
    AddlProps

  class WithTheme extends React.Component<OuterProps> {
    render() {
      return (
        <Component
          {...this.props as JSX.LibraryManagedAttributes<C, React.ComponentProps<C>>}
          // this is bad below because `theme` is not typechecked against inner component
          theme={1}
        />
      )
    }
  }
  return WithTheme
}

function withTheme<C extends React.JSXElementConstructor<React.ComponentProps<C> & WithThemeProps>>(
  Component: C
) {
  type OuterProps = JSX.LibraryManagedAttributes<C, Omit<React.ComponentProps<C>, 'theme'>> &
    AddlProps

  class WithTheme extends React.Component<OuterProps> {
    render() {
      const themeProps: WithThemeProps = {
        theme: '',
      }
      return <Component {...this.props as any} {...themeProps} />
    }
  }
  return WithTheme
}

interface MyComponentProps extends WithThemeProps {
  message: string
}

class MyComponent extends React.Component<MyComponentProps> {
  static defaultProps = {
    message: '',
  }

  render() {
    return <div />
  }
}

interface MyBadComponentProps {
  message: string
}

class MyBadComponent extends React.Component<MyBadComponentProps> {
  static defaultProps = {
    message: '',
  }

  render() {
    return <div />
  }
}

const Test = withTheme(MyComponent)
const testEl = <Test />

const FailTest = withTheme(MyBadComponent)

[swyxio]

love it. will do some writing up some time this week. may need a whole cheatsheet just for HOCs, ha.

[ferdaber]

Related issue opened in TS repo: microsoft/TypeScript#29873

[infctr]

cleaner?

function withTheme<
  C extends React.ComponentType<React.ComponentProps<C> & WithThemeProps>,
  ResolvedProps = JSX.LibraryManagedAttributes<C, Omit<React.ComponentProps<C>, keyof WithThemeProps>>
>(
  Component: C
) {
  return class WithTheme extends React.Component<AddlProps & ResolvedProps> {
    render() {
      const themeProps: WithThemeProps = {
        theme: '',
      }

      return (
        <Component 
          {...this.props as JSX.LibraryManagedAttributes<C, React.ComponentProps<C>>} 
          {...themeProps} 
        />
      );
    }
  }
}

@ferdaber thanks for the valid typecast hint!

[infctr]

How about using with react-redux' connect? Typechecking here gets tricky

function withTheme<
  C extends React.ComponentType<React.ComponentProps<C> & WithThemeProps>,
  ResolvedProps = JSX.LibraryManagedAttributes<C, Omit<React.ComponentProps<C>, keyof WithThemeProps>>
>(
  Component: C
) {
  class WithTheme extends React.Component<WithThemeProps & AddlProps & ResolvedProps> {
    render() {
      const { theme, ...props } = this.props;

      return (
        <Component 
          {...props as JSX.LibraryManagedAttributes<C, React.ComponentProps<C>>} 
          theme={theme}
        />
      );
    }
  }

  return connect<WithThemeProps, void, AddlProps & ResolvedProps>(
    () => ({ theme: 'theme' })
  )(WithTheme) // error, types don't match
}

[ferdaber]

If you're just wrapping something with a connect call you should just simplify it:

function withTheme<P extends WithThemeProps>(component: React.ComponentType<P>) {
  return connect(() => ({ theme: 'theme' }))(component)
}

[infctr]

I'm getting same error tho

Argument of type 'ComponentType<P>' is not assignable to parameter of type 'ComponentType<Matching<WithThemeProps & DispatchProp<AnyAction>, P>>'.
  Type 'ComponentClass<P, any>' is not assignable to type 'ComponentType<Matching<WithThemeProps & DispatchProp<AnyAction>, P>>'.
    Type 'ComponentClass<P, any>' is not assignable to type 'ComponentClass<Matching<WithThemeProps & DispatchProp<AnyAction>, P>, any>'.
      Type 'P' is not assignable to type 'Matching<WithThemeProps & DispatchProp<AnyAction>, P>'.
        Type 'WithThemeProps' is not assignable to type 'Matching<WithThemeProps & DispatchProp<AnyAction>, P>'.ts(2345)

[infctr]

@ferdaber And besides this loses inner component's default props

import React from 'react'
import { compose } from 'redux'
import { connect } from 'react-redux'

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>

// wrapper 
export interface WithThemeProps {
  theme: {}
}

interface AddlProps {
  foo: string
}

function withTheme<P extends WithThemeProps>(component: React.ComponentType<P>) {
  return connect<WithThemeProps, void, AddlProps & Omit<P, keyof WithThemeProps>>(() => ({ theme: 'theme' }))(component as React.ComponentType)
}

// component
interface MyComponentProps extends WithThemeProps {
  message: string
  required: string
}

class MyComponent extends React.Component<MyComponentProps> {
  static defaultProps = {
    message: '',
  }

  render() {
    return <div />
  }
}

const Test = withTheme(MyComponent)
const testEl = <Test required="123" foo='123' /> // error, message is missing

Another issue, not sure how it's related, but I've ran into this playing with HOC's and default props

// use with `compose` from redux
const Composed = compose(withTheme)(MyComponent)

const x = <Composed required="123" ></Composed> // error, all component's props are lost

[ferdaber]

I can play around with it, react-redux's types rely heavily on conditional types which don't get inferred very well, I'll take a look.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions!