What is useId Hook in React?

The useId hook, introduced in React 18, is a built-in tool designed to generate unique and stable identifiers for accessibility attributes and DOM elements. This article explains what the useId hook is, why it is essential for modern web development—especially in server-side rendered (SSR) applications—how to implement it in your components, and the common mistakes you should avoid when using it.

Why Do We Need the useId Hook?

Before React 18, generating unique IDs for HTML elements (like linking a <label> to an <input> using the htmlFor and id attributes) was challenging.

Developers often resorted to manual incrementing counters or random number generators like Math.random(). However, these approaches failed in Server-Side Rendering (SSR) environments. If the server generated one ID and the client generated another during hydration, it resulted in a “hydration mismatch” error.

The useId hook solves this problem by generating a stable, unique ID that is identical on both the server and the client, ensuring seamless hydration.

How to Use useId

Using the useId hook is straightforward. You import it from React and call it inside your functional component to get a unique ID string.

Here is a basic example of how to use useId to link a text input with its label:

import { useId } from 'react';

function LoginForm() {
  const emailId = useId();

  return (
    <div>
      <label htmlFor={emailId}>Email Address:</label>
      <input id={emailId} type="email" />
    </div>
  );
}

In this example, React guarantees that the value of emailId will be unique across your entire application and will remain consistent between the server rendering and client-side rendering.

Handling Multiple Fields in One Component

You do not need to call useId for every single input field in a large form. Instead, you can call useId once to generate a base ID and append distinct suffixes for each specific element. This keeps your code clean and improves performance.

import { useId } from 'react';

function RegistrationForm() {
  const baseId = useId();

  return (
    <form>
      <div>
        <label htmlFor={`${baseId}-firstName`}>First Name</label>
        <input id={`${baseId}-firstName`} type="text" />
      </div>
      <div>
        <label htmlFor={`${baseId}-lastName`}>Last Name</label>
        <input id={`${baseId}-lastName`} type="text" />
      </div>
    </form>
  );
}

Important Limitations: What useId is Not For

While useId is incredibly useful, it is important to know when not to use it: