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How to remove Object is possibly ‘null’ TS2531 warning when using PropTypes.InferProps and default parameters?

David Horm

I have a simple React component that adds two numbers together. It’s written in TypeScript and using @types/prop-types.

import React from 'react';
import PropTypes from 'prop-types';

const AddPropsTypes = {
  first: PropTypes.number,
  second: PropTypes.number
};

type Props = PropTypes.InferProps<typeof AddPropsTypes>;
const Add: React.FC<Props> = ({ first = 1, second = 2 }) => {
  return <div>{first + second}</div>;
};

Add.propTypes = AddPropsTypes;

export default Add;

Typescript complains that first and second could possibly be ‘null’ ts(2531), but they have default parameter values.

Making these PropTypes.number.isRequired will obviously make the warning go away, but I don’t want them required.

I know I can make this warning go away with <div>{(first || 1) + (second || 2)}</div> within the jsx, but I shouldn’t have to define the default values twice. Currently, I’m ignoring the warning with the following above the line:

{/* lol https://github.com/Microsoft/TypeScript/issues/27552
// @ts-ignore */}

Is there any way to define the PropTypes or InferProps so it knows about the default parameter values?

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Answer

Use non null assertion operator !

first! +second!