Understanding useId in React

The useId hook in React is used to generate unique IDs for accessibility attributes like id or htmlFor. It’s especially useful when multiple instances of a component exist, and each instance needs its own unique identifier.

Why useId?

• React ensures that the generated IDs are unique across the app.
• It simplifies creating IDs for elements like forms and ARIA attributes without worrying about collisions.
• It works seamlessly in server-side rendering (SSR) environments to avoid mismatches between client and server.

How useId Works

The useId hook generates a unique string that you can append to identifiers for better readability.

const id = useId();

Key Features of useId

1. Generates a unique identifier per component instance.
2. Ensures IDs are consistent between the server and client in SSR setups.
3. Not reactive — calling it multiple times in a render always returns the same ID for that component instance.

Example

Here is an example where using ids will fail. When we click on the second to last label of the element, it will not take us to the correct input!

import React, { useId } from "react";

const ItemForm = () => {
  return (
    <div>
      <label htmlFor="item">Item</label>
      <input id="item" type="text" />
    </div>
  );
};

const App = () => {
  return (
    <div>
      <h1>Multiple Item Forms</h1>
      <ItemForm />
      <ItemForm />
      <ItemForm />
    </div>
  );
};

export default App;

Here’s an example of using useId to fix it and generate unique id attributes for form inputs:

import React, { useId } from "react";

const ItemForm = () => {
  const id = useId();

  return (
    <div>
      <label htmlFor={`${id}-item`}>Item</label>
      <input id={`${id}-item`} type="text" />
    </div>
  );
};

const App = () => {
  return (
    <div>
      <h1>Multiple Item Forms</h1>
      <ItemForm />
      <ItemForm />
      <ItemForm />
    </div>
  );
};

export default App;

How It Works

• Each ItemForm instance gets a unique id generated by useId.
• For example:
  • The first ItemForm might have IDs like r:0-item.
  • The second ItemForm might have IDs like r:1-item.

When to Use useId

1. Forms and Accessibility:
   • Add unique id attributes for label and input pairs.
   • Create unique aria-labelledby or aria-describedby relationships.
2. Dynamic Components:
   • Use useId for components rendered multiple times in lists.
3. SSR Compatibility:
   • Ensures IDs match between server and client, avoiding hydration warnings.

Limitations

• useId is not reactive — it generates the same ID throughout the component’s lifecycle.
• Use it only for static unique identifiers. For dynamic or changing IDs, consider using useState or a library like uuid.

Summary

• Purpose: Generate unique, collision-free IDs for components.
• Use Case: Accessibility (id, htmlFor, ARIA), forms, or dynamic lists.
• Advantages:
  • Simplifies ID generation.
  • Handles SSR compatibility.
  • Avoids manual ID management.

Let me know if you’d like more examples or details! 🚀