Props Validation in React

1. What Are Props in React?

props (short for "properties") are a mechanism for passing data and event handlers from one component to another, typically from a parent component to a child component.

Parent component

import React from 'react';

const App = () => {
  return (
    <div>
      <Greeting name="Alice" />
      <Greeting name="Bob" />
    </div>
  );
};

export default App;

Child component that receives props

const Greeting = (props) => {
  return <h1>Hello, {props.name}!</h1>;
};

2. Why Validate Props?

Validating props ensures that a component receives the correct type of data, and the required props are provided. This helps to:

• Prevent bugs.

• Make the component more predictable

For example, if a component expects a string but receives a number, it could lead to unexpected behavior.

3. Using PropTypes for Validation

React provides a package called prop-types that allows you to enforce prop validation. If the props passed to the component do not match the expected types, React will log warnings in the console.

4. Installing prop-types Package

If you’re working in a new React project, you might need to install the prop-types package first:

npm install prop-types

5. Defining PropTypes in a Component

You can define prop types by adding the propTypes object to your component.

import PropTypes from 'prop-types';

function Greeting(props) {
  return <h1>Hello, {props.name}!</h1>;
}

Greeting.propTypes = {
  name: PropTypes.string.isRequired,
};

here: Adding PropTypes to validate the "name" prop
Expecting "name" to be a required string

6. Common PropTypes

Here are some common types of prop validations you can apply:

1. Primitive Types:

• PropTypes.string - Ensures the prop is a string.
• PropTypes.number - Ensures the prop is a number.
• PropTypes.bool - Ensures the prop is a boolean.
• PropTypes.func - Ensures the prop is a function.
• PropTypes.object - Ensures the prop is an object.
• PropTypes.array - Ensures the prop is an array.
• PropTypes.node - Ensures the prop is any renderable content (numbers, strings, elements,

2. Required Props: Use .isRequired to enforce that a prop is passed:

Greeting.propTypes = {
  name: PropTypes.string.isRequired,
};

3. Arrays of a Certain Type: You can validate arrays to ensure their contents are of a specific type:

MyComponent.propTypes = {
  items: PropTypes.arrayOf(PropTypes.string).isRequired, // Array of strings
};

4. Objects of a Certain Shape:

MyComponent.propTypes = {
  user: PropTypes.shape({
    name: PropTypes.string,
    age: PropTypes.number,
  }).isRequired,
};

5. One of a Set of Values: You can enforce that a prop is one of several specified values:

MyComponent.propTypes = {
  status: PropTypes.oneOf(['success', 'error', 'loading']).isRequired,
};

6. Custom Prop Validation: You can create your own custom validation logic:

MyComponent.propTypes = {
  age: function (props, propName, componentName) {
    if (props[propName] < 18) {
      return new Error(
        `${propName} in ${componentName} must be at least 18 years old`
      );
    }
  },
};

7. Example of Validating Props

Let’s create a component that expects several types of props and validate them:

import PropTypes from 'prop-types';

function Profile({ name, age, hobbies, status }) {
  return (
    <div>
      <h2>{name}</h2>
      <p>Age: {age}</p>
      <p>Hobbies: {hobbies.join(', ')}</p>
      <p>Status: {status}</p>
    </div>
  );
}

Profile.propTypes = {
  name: PropTypes.string.isRequired,
  age: PropTypes.number,
  hobbies: PropTypes.arrayOf(PropTypes.string).isRequired,
  status: PropTypes.oneOf(['active', 'inactive', 'pending']).isRequired,
};

function App() {
  return (
    <Profile
      name="John Doe"
      age={30}
      hobbies={['Reading', 'Traveling', 'Swimming']}
      status="active"
    />
  );
}

export default App;

8. Default Props

You can also define default props using defaultProps in case a prop isn't provided.

Profile.defaultProps = {
  age: 18, // Default age if not provided
};

9. Handling Invalid Prop Types

If a prop type is incorrect, React will log a warning in the browser console, but the application will still work. It’s important to note that PropTypes only run in development mode (i.e., they do not run in production builds).