Tell us about the useId hook, how it works, where it's applied and for what purpose?

Brief Answer

useId is a React hook that generates unique IDs that are stable across the server and client. It’s primarily used to create accessible HTML attributes like id and aria-* that need to match between server-rendered and client-rendered content.

Syntax: const id = useId();

Key features:

Generates unique IDs consistent between server and client
Solves accessibility issues with SSR/CSR mismatch
Works with React’s concurrent rendering features
Provides deterministic IDs based on component position

Usage example:

function AccessibleComponent() {
  const id = useId();
  
  return (
    <div>
      <label htmlFor={id}>Name:</label>
      <input id={id} type="text" />
    </div>
  );
}

Full Answer

The useId hook is one of React’s built-in hooks designed to generate unique IDs that remain consistent between server-side rendering (SSR) and client-side rendering (CSR). It solves common accessibility issues that arise when HTML attributes like id don’t match between server-rendered and client-rendered content. 🚀

How useId works?

useId generates a unique string ID that:

Remains the same between server and client renders
Is deterministic based on component position in the tree
Automatically handles concurrent rendering scenarios

import React, { useId } from 'react';
 
function Component() {
  const id = useId();
  
  return (
    <div>
      <label htmlFor={id}>Input label</label>
      <input id={id} type="text" />
    </div>
  );
}

When the component renders:

React generates a unique ID based on component position
The same ID is generated on both server and client
ID remains stable across re-renders
Concurrent rendering doesn’t affect ID consistency

Main useId applications

1. Accessible form labels

function AccessibleForm() {
  const nameId = useId();
  const emailId = useId();
  
  return (
    <form>
      <label htmlFor={nameId}>Full name:</label>
      <input id={nameId} type="text" name="name" />
      
      <label htmlFor={emailId}>Email:</label>
      <input id={emailId} type="email" name="email" />
    </form>
  );
}

2. Accessible ARIA attributes

function Accordion() {
  const accordionId = useId();
  const [isOpen, setIsOpen] = useState(false);
  
  return (
    <div>
      <button
        aria-expanded={isOpen}
        aria-controls={`${accordionId}-content`}
        onClick={() => setIsOpen(!isOpen)}
      >
        Toggle accordion
      </button>
      
      <div
        id={`${accordionId}-content`}
        aria-hidden={!isOpen}
      >
        Accordion content
      </div>
    </div>
  );
}

function Modal({ isOpen, onClose, children }) {
  const modalId = useId();
  const titleId = useId();
  
  if (!isOpen) return null;
  
  return (
    <div 
      role="dialog" 
      aria-labelledby={titleId}
      aria-describedby={modalId}
    >
      <h2 id={titleId}>Modal Title</h2>
      <div id={modalId}>{children}</div>
      <button onClick={onClose}>Close</button>
    </div>
  );
}

When to use useId

✅ Use useId when:

Creating accessible HTML attributes — labels, ARIA attributes
Server-side rendering — ensuring ID consistency between server and client
Dynamic ID generation — when you need unique IDs for components
Accessibility compliance — meeting WCAG standards for labeling

function AccessibleComponent() {
  const id = useId();
  
  return (
    <div>
      <label htmlFor={id}>Description:</label>
      <textarea id={id} name="description" />
    </div>
  );
}

When to avoid useId

❌ Avoid useId when:

Static IDs — when you can hardcode IDs
Non-accessibility use cases — for general unique identifiers
Simple components — without accessibility requirements
When IDs don’t need to be unique — in isolated scopes

// ❌ Don't use useId unnecessarily
function SimpleComponent() {
  const id = useId(); // Not needed for simple styling
  
  return <div id={id} className="simple-div">Content</div>;
}
 
// ✅ Just use static IDs
function SimpleComponent() {
  return <div id="simple-div" className="simple-div">Content</div>;
}

Common mistakes

1. Using useId for non-accessibility purposes

// ❌ Misuse for general unique IDs
function Component() {
  const uniqueId = useId();
  
  return (
    <div data-id={uniqueId}>
      {/* Using ID for data tracking instead of accessibility */}
    </div>
  );
}
 
// ✅ Use for accessibility purposes
function Component() {
  const id = useId();
  
  return (
    <div>
      <label htmlFor={id}>Input:</label>
      <input id={id} type="text" />
    </div>
  );
}

2. Calling useId conditionally

// ❌ Error: conditional hook call
function Component({ showLabel }) {
  let id;
  if (showLabel) {
    id = useId(); // Hook called conditionally!
  }
  
  return <div>{showLabel && <label htmlFor={id}>Label</label>}</div>;
}
 
// ✅ Correctly: always call the hook
function Component({ showLabel }) {
  const id = useId(); // Always called
  
  return (
    <div>
      {showLabel && <label htmlFor={id}>Label</label>}
      <input id={id} type="text" />
    </div>
  );
}

3. Using useId in loops without proper scoping

// ❌ Error: same ID for multiple elements
function ListComponent({ items }) {
  const id = useId();
  
  return (
    <div>
      {items.map((item, index) => (
        <div key={index}>
          <label htmlFor={id}>Item {index}:</label>
          <input id={id} type="text" /> {/* Same ID for all inputs! */}
        </div>
      ))}
    </div>
  );
}
 
// ✅ Correctly: each item gets its own ID
function ListComponent({ items }) {
  return (
    <div>
      {items.map((item, index) => (
        <ItemComponent key={index} item={item} index={index} />
      ))}
    </div>
  );
}
 
function ItemComponent({ item, index }) {
  const id = useId();
  
  return (
    <div>
      <label htmlFor={id}>Item {index}:</label>
      <input id={id} type="text" />
    </div>
  );
}

Summary

✅ useId is a React hook for:

Generating unique IDs consistent between server and client
Solving accessibility issues with SSR/CSR mismatch
Creating accessible HTML attributes (labels, ARIA)
Ensuring ID stability across re-renders

✅ When to use:

Creating accessible form labels and inputs
Generating ARIA attributes for screen readers
Server-side rendering with ID consistency requirements
Accessibility compliance in dynamic components

❌ When to avoid:

Static IDs that can be hardcoded
Non-accessibility use cases
Simple components without accessibility needs
When IDs don’t need to be globally unique

✅ Best practices:

Use only for accessibility purposes
Always call useId at the top level of components
Don’t call useId conditionally
Each component instance should get its own ID

useId is a specialized hook for accessibility scenarios, particularly important in server-side rendered applications. Use it when you need to ensure consistent IDs between server and client for proper accessibility. 🚀

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