Since JavaScript is a dynamically typed language, we don’t really have a way to enforce the type of a variable at compile time, and if we pass invalid types, they will fail at runtime or give weird results if the types are compatible but not what we expect.

Flow and TypeScript help a lot, but React has a way to directly help with props types, and even before running the code, our tools (editors, linters) can detect when we are passing the wrong values:

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

class BlogPostExcerpt extends Component {
  render() {
    return (
      <div>
        <h1>{this.props.title}</h1>
        <p>{this.props.description}</p>
      </div>
    )
  }
}

BlogPostExcerpt.propTypes = {
  title: PropTypes.string,
  description: PropTypes.string
}

export default BlogPostExcerpt

Which types can we use

These are the fundamental types we can accept:

• PropTypes.array
• PropTypes.bool
• PropTypes.func
• PropTypes.number
• PropTypes.object
• PropTypes.string
• PropTypes.symbol

We can accept one of two types:

PropTypes.oneOfType([
  PropTypes.string,
  PropTypes.number
]),

We can accept one of many values:

PropTypes.oneOf(['Test1', 'Test2']),

We can accept an instance of a class:

PropTypes.instanceOf(Something)

We can accept any React node:

PropTypes.node

or even any type at all:

PropTypes.any

Arrays have a special syntax that we can use to accept an array of a particular type:

PropTypes.arrayOf(PropTypes.string)

Objects, we can compose an object properties by using

PropTypes.shape({
  color: PropTypes.string,
  fontSize: PropTypes.number
})

Requiring properties

Appending isRequired to any PropTypes option will cause React to return an error if that property is missing:

PropTypes.arrayOf(PropTypes.string).isRequired,
PropTypes.string.isRequired,

Lessons in this unit:

0:	Introduction
1:	Setting up a React project with Vite
2:	React Components
3:	Introduction to JSX
4:	Using JSX to compose UI
5:	The difference between JSX and HTML
6:	Embedding JavaScript in JSX
7:	Handling user events
8:	Install the React Developer Tools
9:	Getting started with JSX
10:	How to return multiple elements in JSX
11:	How to learn React
12:	Should you use jQuery or React?
13:	React concepts: declarative
14:	The Virtual DOM
15:	The roadmap to learn React
16:	What’s new in React 19
17:	How to install React
18:	The React Fragment
19:	React, how to transfer props to child components
20:	▶︎ React PropTypes
21:	React DOM events on components
22:	How to pass a parameter to event handlers in React