React render props pattern class errors

Help please.
it is assumed that the component can be used like this:

<MouseCoordinates></MouseCoordinates>

or

<MouseCoordinates>
{(x,y) => { ... }}
</MouseCoordinates>


I don't understand what does it want.
Here is the code:

import React, { MouseEvent } from 'react';

const initialState = { x: 0, y: 0 };
const defaultProps = {
children: (args: TMouseCoordinates) => null,
};

type TMouseCoordinates = typeof initialState;
type TDefaultProps = typeof defaultProps;

type TState = Readonly<TMouseCoordinates>;
type TProps = Partial<
{
children?: (coordinates: TMouseCoordinates) => JSX.Element;
} & TDefaultProps
>;

class MouseCoordinates extends React.Component<TProps, TState> {
static readonly defaultProps: TProps = defaultProps;
^^^^^^^^^^^^

readonly state: TMouseCoordinates = initialState;

componentDidMount() {
document.addEventListener('mousemove', this.handleMouseMove);
^^^^^^^^^^^^^^^^^^^^
}

componentWillUnmount() {
document.removeEventListener('mousemove', this.handleMouseMove);
^^^^^^^^^^^^^^^^^^^^
}

handleMouseMove = (event: MouseEvent<HTMLElement>): void => {
const { screenX = 0, screenY = 0 } = event;

this.setState(() => ({
x: screenX,
y: screenY,
}));
};

render() {
const { children } = this.props;
const isRenderIsFunction = typeof this.props.children === 'function';

return isRenderIsFunction ? children(this.state) : null;
^^^^^^^^^^^^^^^^^^^^
}
}


I have strange errors at:

static readonly defaultProps: TProps = defaultProps;


Type '{ children: (args: { x: number; y: number; }) => null; }' is not
assignable to type 'Partial<{ children?: ((coordinates: { x: number;
y: number; }) => Element) | undefined; } & { chi...'. Types of
property 'children' are incompatible.
Type '(args: { x: number; y: number; }) => null' is not assignable to type '(((coordinates: { x: number; y: number; }) => Element) &
((args: { x: number; y: number; }) => nu...'.
Type '(args: { x: number; y: number; }) => null' is not assignable to type '((coordinates: { x: number; y: number; }) =>
Element) & ((args: { x: number; y: number; }) => null)'.
Type '(args: { x: number; y: number; }) => null' is not assignable to type '(coordinates: { x: number; y: number; }) =>
Element'.
Type 'null' is not assignable to type 'Element'.

here is cryptic error at:

document.addEventListener('mousemove', this.handleMouseMove);


"Argument of type '(event: MouseEvent) => void' is not
assignable to parameter of type
'EventListenerOrEventListenerObject'.n Type '(event:
MouseEvent) => void' is not assignable to type
'EventListenerObject'.n Property 'handleEvent' is missing in type
'(event: MouseEvent) => void'.",

and last

return isRenderIsFunction ? children(this.state) : null;


Cannot invoke an object which is possibly 'undefined'.

defaultProps

children

null

TProps

children

JSX.Element

strictNullChecks

null

undefined

3 Answers
3

type TProps = Partial<
{
children?: (coordinates: TMouseCoordinates) => JSX.Element;
} & {
children: (args: TMouseCoordinates) => null,
}>;


so you simple say: children props is required and not and contain both functions: (args: TMouseCoordinates) => null and (coordinates: TMouseCoordinates) => JSX.Element its simple has no sense.

children

(args: TMouseCoordinates) => null

(coordinates: TMouseCoordinates) => JSX.Element

i guess this is the interface you need:

interface Props{
children?: (args: TMouseCoordinates) => (JSX.Element | null)
}


MouseEvent should not be imported from React

MouseEvent

Here is the correct code:

import React from 'react';

export type TMouseEventRenderer = (coordinates: ICoordinates) => JSX.Element | null;

const initialState = { x: 0, y: 0 };
const defaultProps = {
children: (() => null) as TMouseEventRenderer,
};

type TDefaultProps = typeof defaultProps;
type TProps = Readonly<{ children?: TMouseEventRenderer } & TDefaultProps>;
type TState = Readonly<ICoordinates>;

class MouseCoordinates extends React.Component<TProps, TState> {
static readonly defaultProps: TDefaultProps = defaultProps;
readonly state: TState = initialState;

componentDidMount() {
document.addEventListener('mousemove', this.handleMouseMove);
}

componentWillUnmount() {
document.removeEventListener('mousemove', this.handleMouseMove);
}

handleMouseMove = (event: MouseEvent): void => {
const { screenX = 0, screenY = 0 } = event;

window.requestAnimationFrame(() => {
this.setState(() => ({
x: screenX,
y: screenY,
}));
});
};

render() {
const { children } = this.props;
const isRenderIsFunction = typeof this.props.children === 'function';

return isRenderIsFunction ? children(this.state) : null;
}
}


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