HOC类型可以通过自身的特性来增强组件吗？

Question

I'm trying to type an Higher Order Component (HOC) using Recompose and its HOC type, using Flow.

This is my code:

// @flow
import React from 'react';
import { compose, defaultProps, withProps, type HOC } from 'recompose';

type InnerProps = {
  text: string,
  num: number,
};

type EnhancedComponentProps = {
  text: string,
};

const baseComponent = ({ text, num }: InnerProps) => (
  <div>
    {text}
    {num}
  </div>
);

const enhance: HOC<*, EnhancedComponentProps> = compose(
  defaultProps({
    text: 'world',
  }),
  withProps(({ text }) => ({
    text: `Hello ${text}`,
  }))
);

export default enhance(baseComponent);

Right now this fails with:

Cannot call enhance with baseComponent bound to a because property num is missing in object type [1] but exists in
InnerProps [2] in the first argument.

     src/Text.js
 [2] 14│ const baseComponent = ({ text, num }: InnerProps) => (
       :
     27│   }))
     28│ );
     29│
     30│ export default enhance(baseComponent);
     31│

     flow-typed/npm/recompose_v0.x.x.js
 [1] 95│   ): HOC<{ ...$Exact<Enhanced>, ...BaseAdd }, Enhanced>;

Trying to read the docs and some blog posts I couldn't reach to a solution. All the examples I find are very trivial and none of them cover this simple case.

What's the right way to type this code?

Answer 1

I guess you get the right error. It says:

num is missing in object type [1] but exists in InnerProps [2] in the first argument.

You declared that your HOC will get what's in EnhancedComponentProps which is missing the num . In other words, you try to extract num from Object that will only get what's declared in EnhancedComponentProps type.

Based on recompose docs: you should get this work by:

// @flow
import React from 'react';
import { compose, defaultProps, withProps, type HOC } from 'recompose';

type EnhancedComponentProps = {
  text: string,
  num: number,
};

const baseComponent = ({ text, num }: EnhancedComponentProps) => ( // in the example from recompose this typing is unnecessary though
  <div>
    {text}
    {num}
  </div>
);

const enhance: HOC<*, EnhancedComponentProps> = compose(
  defaultProps({
    text: 'world',
  }),
  withProps(({ text }) => ({
    text: `Hello ${text}`,
  }))
);

export default enhance(baseComponent);