React Portals

React Portals provide a way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. This feature is particularly useful for cases where you need to render content that visually "breaks out" of its container, such as modals, tooltips, and popovers. This chapter will cover everything you need to know about React Portals, from the basics to advanced use cases, ensuring a comprehensive understanding.

Understanding the Need for Portals

Common Scenario

In web development, there are instances where we need to render components outside the normal DOM hierarchy. For example:

  • Modals: Overlays that should appear above the rest of the content.
  • Tooltips: Small boxes that appear above or next to elements.
  • Dropdowns: Menus that need to appear above other content.

The Problem

Rendering such components within the normal DOM hierarchy can cause issues with styling and positioning. Without portals, you might have to deal with CSS z-index or position conflicts.

What are React Portals?

React Portals provide a way to render children into a DOM node that exists outside the DOM hierarchy of the parent component. This allows components to visually break out of their containers while maintaining their logical parent-child relationship in React’s component tree.

Key Points

  • DOM Hierarchy: Portals allow rendering outside the normal DOM hierarchy.
  • Logical Hierarchy: Maintains logical hierarchy within the React component tree.
  • Use Cases: Ideal for modals, tooltips, and other UI elements that need to overlay other content.

Creating a Portal

Basic Syntax

Creating a portal involves using the ReactDOM.createPortal method.

				
					ReactDOM.createPortal(child, container)
  • child: The React element to be rendered.
  • container: The DOM node where the child should be rendered.

Example: Simple Portal

App Structure

index.html: Create a container for the portal.

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>React Portal Example</title>
</head>
<body>
  <div id="root"></div>
  <div id="portal-root"></div>  <script data-no-optimize="1">!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t="undefined"!=typeof globalThis?globalThis:t||self).LazyLoad=e()}(this,function(){"use strict";function e(){return(e=Object.assign||function(t){for(var e=1;e<arguments.length;e++){var n,a=arguments[e];for(n in a)Object.prototype.hasOwnProperty.call(a,n)&&(t[n]=a[n])}return t}).apply(this,arguments)}function i(t){return e({},it,t)}function o(t,e){var n,a="LazyLoad::Initialized",i=new t(e);try{n=new CustomEvent(a,{detail:{instance:i}})}catch(t){(n=document.createEvent("CustomEvent")).initCustomEvent(a,!1,!1,{instance:i})}window.dispatchEvent(n)}function l(t,e){return t.getAttribute(gt+e)}function c(t){return l(t,bt)}function s(t,e){return function(t,e,n){e=gt+e;null!==n?t.setAttribute(e,n):t.removeAttribute(e)}(t,bt,e)}function r(t){return s(t,null),0}function u(t){return null===c(t)}function d(t){return c(t)===vt}function f(t,e,n,a){t&&(void 0===a?void 0===n?t(e):t(e,n):t(e,n,a))}function _(t,e){nt?t.classList.add(e):t.className+=(t.className?" 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</html>

App.js: Create a component that uses a portal.

				
					// src/App.js
import React from 'react';
import ReactDOM from 'react-dom';
import Modal from './Modal';

function App() {
  const [showModal, setShowModal] = React.useState(false);

  const toggleModal = () => setShowModal(!showModal);

  return (
    <div className="App">
      <h1>React Portal Example</h1>
      <button onClick={toggleModal}>
        {showModal ? 'Hide' : 'Show'} Modal
      </button>
      {showModal && <Modal />}
    </div>
  );
}

export default App;

Modal.js: Define the modal component that uses a portal.

				
					// src/Modal.js
import React from 'react';
import ReactDOM from 'react-dom';

const modalRoot = document.getElementById('portal-root');

function Modal() {
  return ReactDOM.createPortal(
    <div style={modalStyle}>
      <h2>Modal Title</h2>
      <p>This is a modal rendered using a React Portal.</p>
    </div>,
    modalRoot
  );
}

const modalStyle = {
  position: 'fixed',
  top: '50%',
  left: '50%',
  transform: 'translate(-50%, -50%)',
  padding: '20px',
  backgroundColor: 'white',
  boxShadow: '0 4px 8px rgba(0, 0, 0, 0.2)',
  zIndex: 1000,
};

export default Modal;

Explanation

  • Portal Root: A separate div with id portal-root in index.html serves as the container for the portal.
  • createPortal: The Modal component uses ReactDOM.createPortal to render its children into the portal-root container.

Output

When you click the “Show Modal” button, a modal will appear centered on the screen, overlaying other content. Clicking the button again hides the modal.

Working with Portals

Complex Structures

Portals can handle more complex structures and components.

Example: Nested Components in a Portal

				
					// src/NestedPortal.js
import React from 'react';
import ReactDOM from 'react-dom';

const portalRoot = document.getElementById('portal-root');

function NestedPortal() {
  return ReactDOM.createPortal(
    <div style={portalStyle}>
      <h2>Nested Portal</h2>
      <p>This portal contains nested components.</p>
      <NestedComponent />
    </div>,
    portalRoot
  );
}

function NestedComponent() {
  return <div style={nestedStyle}>I am a nested component inside the portal.</div>;
}

const portalStyle = {
  position: 'fixed',
  top: '40%',
  left: '50%',
  transform: 'translate(-50%, -40%)',
  padding: '20px',
  backgroundColor: 'lightblue',
  boxShadow: '0 4px 8px rgba(0, 0, 0, 0.2)',
  zIndex: 1000,
};

const nestedStyle = {
  marginTop: '10px',
  padding: '10px',
  backgroundColor: 'white',
  border: '1px solid #ccc',
};

export default NestedPortal;

Explanation

  • Nested Components: NestedPortal renders NestedComponent inside the portal.
  • Style Customization: Styles can be customized to match the needs of nested components.

Output

When NestedPortal is rendered, it shows a styled box containing another styled component, all rendered outside the normal DOM hierarchy.

Advanced Usage of Portals

Multiple Portals

You can create multiple portals in a single application, each rendering to different DOM nodes.

				
					// src/MultiplePortals.js
import React from 'react';
import ReactDOM from 'react-dom';

const portalRoot1 = document.getElementById('portal-root1');
const portalRoot2 = document.getElementById('portal-root2');

function MultiplePortals() {
  return (
    <>
      {ReactDOM.createPortal(
        <div style={portalStyle1}>
          <h2>Portal 1</h2>
          <p>Content for portal 1.</p>
        </div>,
        portalRoot1
      )}
      {ReactDOM.createPortal(
        <div style={portalStyle2}>
          <h2>Portal 2</h2>
          <p>Content for portal 2.</p>
        </div>,
        portalRoot2
      )}
    </>
  );
}

const portalStyle1 = {
  position: 'fixed',
  top: '30%',
  left: '50%',
  transform: 'translate(-50%, -30%)',
  padding: '20px',
  backgroundColor: 'lightcoral',
  boxShadow: '0 4px 8px rgba(0, 0, 0, 0.2)',
  zIndex: 1000,
};

const portalStyle2 = {
  position: 'fixed',
  top: '60%',
  left: '50%',
  transform: 'translate(-50%, -60%)',
  padding: '20px',
  backgroundColor: 'lightgreen',
  boxShadow: '0 4px 8px rgba(0, 0, 0, 0.2)',
  zIndex: 1000,
};

export default MultiplePortals;

Explanation

  • Multiple Containers: Two separate portal roots (portal-root1 and portal-root2) are used to render different content.
  • Styling and Positioning: Each portal has its own styling and positioning.

Output

Two different pieces of content are rendered at different positions on the screen, each managed by a separate portal.

Managing Events with Portals

Event Bubbling

Events in portals propagate through the React component tree, even if they are not in the same DOM tree.

				
					// src/ModalWithEvents.js
import React from 'react';
import ReactDOM from 'react-dom';

const portalRoot = document.getElementById('portal-root');

function ModalWithEvents({ onClose }) {
  return ReactDOM.createPortal(
    <div style={modalStyle} onClick={onClose}>
      <div style={modalContentStyle} onClick={(e) => e.stopPropagation()}>
        <h2>Modal with Events</h2>
        <p>Click outside to close.</p>
      </div>
    </div>,
    portalRoot
  );
}

const modalStyle = {
  position: 'fixed',
  top: 0,
  left: 0,
  width: '100%',
  height: '100%',
  backgroundColor: 'rgba(0, 0, 0, 0.5)',
  display: 'flex',
  justifyContent: 'center',
  alignItems: 'center',
  zIndex: 1000,
};

const modalContentStyle = {
  padding: '20px',
  backgroundColor: 'white',
  borderRadius: '5px',
};

export default ModalWithEvents;

Explanation

  • Event Bubbling: Clicking outside the modal content triggers the onClose handler.
  • Event Propagation: stopPropagation prevents the click event from bubbling up to the parent.

Output

A modal with an overlay that closes when you click outside the modal content.

Best Practices for Using Portals

Key Points

  • Accessibility: Ensure that portal content is accessible (e.g., focus management for modals).
  • Styling: Manage styles to prevent conflicts with the surrounding content.
  • Performance: Be mindful of performance when using multiple portals.

Use Cases

  • Modals: For dialogs and pop-up windows.
  • Tooltips: For hover information boxes.
  • Dropdowns: For menus that need to appear above other content.

Example: Creating a Tooltip with Portals

Complete Implementation

  1. index.html: Add a portal container.
				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>React Portal Tooltip</title>
</head>
<body>
  <div id="root"></div>
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</html>
  1. App.js: Main application component.
				
					// src/App.js
import React from 'react';
import Tooltip from './Tooltip';

function App() {
  return (
    <div className="App">
      <h1>React Portal Tooltip Example</h1>
      <Tooltip text="This is a tooltip">
        <button>Hover over me</button>
      </Tooltip>
    </div>
  );
}

export default App;
  1. Tooltip.js: Tooltip component.
				
					// src/Tooltip.js
import React, { useState, useEffect, useRef } from 'react';
import ReactDOM from 'react-dom';

const portalRoot = document.getElementById('portal-root');

function Tooltip({ children, text }) {
  const [visible, setVisible] = useState(false);
  const [position, setPosition] = useState({ top: 0, left: 0 });
  const ref = useRef();

  useEffect(() => {
    const handleMouseOver = () => {
      const rect = ref.current.getBoundingClientRect();
      setPosition({
        top: rect.top + window.scrollY - 30,
        left: rect.left + window.scrollX,
      });
      setVisible(true);
    };

    const handleMouseOut = () => {
      setVisible(false);
    };

    const node = ref.current;
    node.addEventListener('mouseover', handleMouseOver);
    node.addEventListener('mouseout', handleMouseOut);

    return () => {
      node.removeEventListener('mouseover', handleMouseOver);
      node.removeEventListener('mouseout', handleMouseOut);
    };
  }, []);

  return (
    <>
      {React.cloneElement(children, { ref })}
      {visible &&
        ReactDOM.createPortal(
          <div style={{ ...tooltipStyle, top: position.top, left: position.left }}>
            {text}
          </div>,
          portalRoot
        )}
    </>
  );
}

const tooltipStyle = {
  position: 'absolute',
  backgroundColor: 'black',
  color: 'white',
  padding: '5px',
  borderRadius: '3px',
  fontSize: '12px',
  zIndex: 1000,
};

export default Tooltip;

Explanation

  • Tooltip Position: Calculate the position of the tooltip based on the target element’s position.
  • Event Handling: Show and hide the tooltip based on mouse events.

Output

A button with a tooltip that appears when you hover over it, demonstrating the use of portals for creating tooltips.

Key Takeaways

  • DOM Hierarchy: Portals render content outside the normal DOM hierarchy but maintain the logical React component hierarchy.
  • Event Handling: Events in portals propagate through the React tree as expected.
  • Use Cases: Ideal for modals, tooltips, dropdowns, and other overlay elements.
  • Advanced Usage: Can manage complex nested structures and multiple portals.

React Portals provide a powerful mechanism for rendering components outside the normal DOM hierarchy, making them ideal for creating overlays, modals, tooltips, and other UI elements that need to visually break out of their parent containers. By understanding and utilizing React Portals, you can create more flexible and maintainable UIs.Happy coding !❤️

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