Understanding PropTypes and defaultProps

Oct 13, 2025 by pynkocean.com 35 views

Introduction

In this article, we will be discussing the concept of type checking in React using PropTypes. However, before we dive into the details, it's essential to note that PropTypes and defaultProps do not work in React version 19 and above. This means that if you're using a version of React greater than 19, you won't be able to use PropTypes and defaultProps in your functional components, and in class components, defaultProps will work, but PropTypes won't.

Understanding PropTypes and defaultProps

PropTypes is a library in React that allows you to specify the types of the props that a component expects. This helps in catching type-related errors at runtime and provides a clear understanding of the expected props for a component. defaultProps, on the other hand, is a feature in React that allows you to specify default values for the props of a component.

Why PropTypes and defaultProps don't work in React version 19 and above

In React version 19 and above, PropTypes and defaultProps have been removed. This means that you won't be able to use them in your functional components, and in class components, defaultProps will work, but PropTypes won't. This change was made to improve the performance and reduce the bundle size of React applications.

Possible ways to fix this

There are a few possible ways to fix this issue:

Install a version of React lesser than 19: One way to fix this issue is to install a version of React lesser than 19. This will allow you to use PropTypes and defaultProps in your functional components and class components.
Remove the whole propTypes and defaultProps concept: Another way to fix this issue is to remove the whole propTypes and defaultProps concept. This means that you will need to use TypeScript or another type checking system to specify the types of the props that a component expects.

Why TypeScript is a better option

TypeScript is a statically typed language that allows you to specify the types of the props that a component expects. This helps in catching type-related errors at compile time and provides a clear understanding of the expected props for a component. TypeScript is a better option than PropTypes and defaultProps because it provides more features and better performance.

How to use TypeScript in React

To use TypeScript in React, you will need to install the @types/react package and configure your project to use TypeScript. Here are the steps to follow:

Install the @types/react package: Run the following command in your terminal to install the @types/react package:

npm install --save-dev @types/react


2.  **Configure your project to use TypeScript**: Create a tsconfig.json file in the root of your project and configure it to use TypeScript. Here is an example tsconfig.json file:

    ```json
{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "outDir": "./dist",
    "strict": true,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true
  }
}

Create a new file with a .ts extension: Create a new file with a .ts extension and start writing your React code in TypeScript.

Conclusion

In conclusion, PropTypes and defaultProps do not work in React version 19 and above. This means that you won't be able to use them in your functional components, and in class components, defaultProps will work, but PropTypes won't. There are a few possible ways to fix this issue, including installing a version of React lesser than 19 and removing the whole propTypes and defaultProps concept. However, TypeScript is a better option than PropTypes and defaultProps because it provides more features and better performance. To use TypeScript in React, you will need to install the @types/react package and configure your project to use TypeScript.

Example Use Case

Here is an example use case of using TypeScript in React:

import React from 'react';

interface Props {
  name: string;
  age: number;
}

const Person: React.FC<Props> = ({ name, age }) => {
  return (
    <div>
      <h1>{name}</h1>
      <p>Age: {age}</p>
    </div>
  );
};

export default Person;

Q&A

Q: What is the difference between PropTypes and defaultProps?

A: PropTypes is a library in React that allows you to specify the types of the props that a component expects. defaultProps, on the other hand, is a feature in React that allows you to specify default values for the props of a component.

Q: Why were PropTypes and defaultProps removed from React version 19 and above?

A: PropTypes and defaultProps were removed from React version 19 and above to improve the performance and reduce the bundle size of React applications.

Q: What is the alternative to PropTypes and defaultProps?

A: The alternative to PropTypes and defaultProps is TypeScript. TypeScript is a statically typed language that allows you to specify the types of the props that a component expects. This helps in catching type-related errors at compile time and provides a clear understanding of the expected props for a component.

Q: How do I install TypeScript in my React project?

A: To install TypeScript in your React project, you will need to install the @types/react package and configure your project to use TypeScript. Here are the steps to follow:

Install the @types/react package: Run the following command in your terminal to install the @types/react package:

npm install --save-dev @types/react


2.  **Configure your project to use TypeScript**: Create a tsconfig.json file in the root of your project and configure it to use TypeScript. Here is an example tsconfig.json file:

    ```json
{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "outDir": "./dist",
    "strict": true,
    "esModuleInterop": true,
    "allowSyntheticDefaultImports": true
  }
}

Create a new file with a .ts extension: Create a new file with a .ts extension and start writing your React code in TypeScript.

Q: What are the benefits of using TypeScript in React?

A: The benefits of using TypeScript in React include:

Improved type safety: TypeScript helps in catching type-related errors at compile time, which improves the overall quality of your code.
Better code completion: TypeScript provides better code completion, which makes it easier to write code.
Improved maintainability: TypeScript makes it easier to maintain your codebase by providing a clear understanding of the expected props for a component.

Q: How do I specify the types of the props that a component expects in TypeScript?

A: To specify the types of the props that a component expects in TypeScript, you will need to define an interface that specifies the types of the props. Here is an example:

interface Props {
  name: string;
  age: number;
}

const Person: React.FC<Props> = ({ name, age }) => {
  return (
    <div>
      <h1>{name}</h1>
      <p>Age: {age}</p>
    </div>
  );
};

In this example, we define a Props interface that specifies the types of the props that the Person component expects. We then use this interface to type the props of the Person component.

Q: How do I specify default values for the props of a component in TypeScript?

A: To specify default values for the props of a component in TypeScript, you will need to use the defaultProps property of the component. Here is an example:

interface Props {
  name: string;
  age: number;
}

const Person: React.FC<Props> = ({ name, age }) => {
  return (
    <div>
      <h1>{name}</h1>
      <p>Age: {age}</p>
    </div>
  );
};

Person.defaultProps = {
  name: 'John Doe',
  age: 30,
};

In this example, we specify default values for the name and age props of the Person component using the defaultProps property.

Conclusion

In conclusion, PropTypes and defaultProps do not work in React version 19 and above. This means that you won't be able to use them in your functional components, and in class components, defaultProps will work, but PropTypes won't. However, TypeScript is a better option than PropTypes and defaultProps because it provides more features and better performance. To use TypeScript in React, you will need to install the @types/react package and configure your project to use TypeScript.