reactjstypescripthigher-order-components

Generic higher-order React component gives type errors


I'm trying to write a generic React component that requires props of one of two types (IFoo or IBar) and a component that accepts props of the selected type.

How come the following doesn't work?

Playground

import React from 'react';

interface IFoo {
  x: string;
}

interface IBar {
  x: number;
}

const foo: React.FunctionComponent<IFoo> = (props: IFoo) => {
  console.log("hello from foo!");
  return <div>foo</div>
};

const bar: React.FunctionComponent<IBar> = (props: IBar) => {
  console.log("hello from bar!");
  return <div>bar</div>
};

interface IProps<T> { 
    props: T[];
    Component: React.FunctionComponent<T>;
}


class HigherOrderComponent<T extends IBar | IFoo> extends React.Component<IProps<T>> { 
    render() {
        const { props, Component } = this.props;
        return (<div>
            {props.map(prop => <Component {...prop}/>)};
        </div>)
     }
}

This returns the following error:

Type 'T' is not assignable to type 'IntrinsicAttributes & T & { children?: ReactNode; }'.
  Type 'IFoo | IBar' is not assignable to type 'IntrinsicAttributes & T & { children?: ReactNode; }'.
    Type 'IFoo' is not assignable to type 'IntrinsicAttributes & T & { children?: ReactNode; }'.
      Type 'IFoo' is not assignable to type 'T'.
        'IFoo' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'IFoo | IBar'.
          Type 'T' is not assignable to type 'IntrinsicAttributes'.
            Type 'IFoo | IBar' is not assignable to type 'IntrinsicAttributes'.
              Type 'IFoo' has no properties in common with type 'IntrinsicAttributes'.(2322)

Solution

  • Quick fix is to add:

    {props.map((prop: T & {}) => <Component {...prop}/>)};
    

    I think the problem is with the spread operator and union type (if there is only one type it works fine). I know TS had problems with that before :(

    Hope this helps :)