Mastering React.createPortal Testing: A Comprehensive Guide
Testing React components can be a breeze, until you introduce React.createPortal. This powerful tool lets you render components outside of the standard DOM hierarchy, but it also throws a curveball when it comes to testing. Fear not, this article will equip you with the knowledge to confidently test your portal-based components.
The Portal Puzzle: Why Testing Gets Tricky
Imagine you have a modal component that needs to appear on top of everything else. This is where React.createPortal comes in. It allows you to render your modal directly into the document.body, ensuring it always stays on top.
Here's a simplified example:
import React from 'react';
import ReactDOM from 'react-dom';
function Modal({ children }) {
return ReactDOM.createPortal(
<div className="modal">
{children}
</div>,
document.body
);
}
function MyComponent() {
return (
<div>
<button onClick={() => setShowModal(true)}>Open Modal</button>
{showModal && <Modal>Hello from the portal!</Modal>}
</div>
);
}
The problem? Traditional testing methods like Enzyme or React Testing Library struggle to find and interact with elements rendered by createPortal. This is because the portal's DOM is detached from the main component's tree.
Unlocking the Portal's Secrets: Testing Strategies
Don't despair! Several strategies can help you overcome this testing hurdle:
1. Dive Deep with document.body:
The simplest solution is to directly query document.body for the portal's elements:
import { render, screen, fireEvent } from '@testing-library/react';
import MyComponent from './MyComponent';
test('opens and closes the modal', () => {
render(<MyComponent />);
// Find the button and click it
const openButton = screen.getByRole('button');
fireEvent.click(openButton);
// Find the modal element directly within document.body
const modalElement = document.body.querySelector('.modal');
expect(modalElement).toBeInTheDocument();
// Find the modal content and test its content
const modalContent = screen.getByText('Hello from the portal!');
expect(modalContent).toBeInTheDocument();
// Close the modal (simulate button click or other closing mechanism)
// ...
});
2. Utilize ReactTestUtils:
React provides a built-in ReactTestUtils module with a handy act function. You can use it to simulate interactions within your portal:
import React from 'react';
import ReactDOM from 'react-dom';
import { act } from 'react-dom/test-utils';
import Modal from './Modal';
test('renders modal content correctly', () => {
// Create a mock container for the portal
const container = document.createElement('div');
document.body.appendChild(container);
// Render the modal inside the container
act(() => {
ReactDOM.render(<Modal>My Portal Content</Modal>, container);
});
// Find the modal element within the container
const modalElement = container.querySelector('.modal');
expect(modalElement).toBeInTheDocument();
// Test modal content
expect(modalElement.textContent).toBe('My Portal Content');
// Clean up the container
document.body.removeChild(container);
});
3. Employ Mocks and Spies:
For testing complex scenarios like user interaction with the portal, consider using mocking and spies.
import { render, screen, fireEvent } from '@testing-library/react';
import MyComponent from './MyComponent';
jest.mock('./Modal', () => {
return jest.fn(() => (
<div className="modal">Mock Modal Content</div>
));
});
test('calls Modal component on button click', () => {
render(<MyComponent />);
const openButton = screen.getByRole('button');
fireEvent.click(openButton);
expect(Modal).toHaveBeenCalledTimes(1);
});
This approach isolates your component logic from the actual portal rendering, allowing you to focus on testing the interaction between components.
4. Leverage Custom Hooks:
For better code organization and reusability, encapsulate the portal logic within a custom hook:
import { useState, useRef, useEffect } from 'react';
import ReactDOM from 'react-dom';
function useModal() {
const [isOpen, setIsOpen] = useState(false);
const modalRef = useRef(null);
useEffect(() => {
if (isOpen) {
const portalElement = document.createElement('div');
document.body.appendChild(portalElement);
modalRef.current = portalElement;
} else {
if (modalRef.current) {
document.body.removeChild(modalRef.current);
modalRef.current = null;
}
}
}, [isOpen]);
const openModal = () => setIsOpen(true);
const closeModal = () => setIsOpen(false);
return {
isOpen,
openModal,
closeModal,
portalElement: modalRef.current,
};
}
function MyComponent() {
const { isOpen, openModal, closeModal, portalElement } = useModal();
return (
<div>
<button onClick={openModal}>Open Modal</button>
{isOpen && ReactDOM.createPortal(
<div className="modal">Hello from the portal!</div>,
portalElement
)}
</div>
);
}
You can now test the hook directly:
import { renderHook } from '@testing-library/react-hooks';
import useModal from './useModal';
test('opens and closes the modal', () => {
const { result } = renderHook(() => useModal());
const { openModal, closeModal, isOpen, portalElement } = result.current;
openModal();
expect(isOpen).toBe(true);
expect(portalElement).toBeInTheDocument();
closeModal();
expect(isOpen).toBe(false);
expect(portalElement).not.toBeInTheDocument();
});
Choosing the Right Approach: A Guide
- If your test needs to directly interact with the portal's DOM, use methods 1 or 2.
- If you want to focus on the logic of your component and avoid dealing with the portal's DOM, use mocking (method 3) or custom hooks (method 4).
- Consider using a combination of these techniques for complex scenarios.
By understanding the quirks of React.createPortal and employing these effective testing strategies, you can confidently build and test robust components that leverage its power.
