Unique IDs

To build accessible forms, you need to ensure that each input element has a globally unique id attribute, and that the corresponding label element has a for attribute that matches the input's id. This allows screen readers to associate the label with the input, making it easier for users to understand the form's structure and purpose. Additionally, it allows users to click on the label to focus the input, which can be especially helpful for users with motor impairments (or like, for everyone you know?).

This gets challenging with reusable components, especially when they're used multiple times on the same page. You can't just hardcode an id value, because then you'd have multiple elements with the same id, which is invalid HTML. You could use a random number or string, but then you'd have to manage that yourself, and it wouldn't be consistent between renders. And if you want to server render your app, you'd have to make sure the ID that's generated on the client matches the one that was generated on the server to avoid bugs which is a pain.

This is where the useId hook comes into play.

The useId hook generates a unique and stable identifier (ID) that you can use for DOM elements.

Here's an example of how you can use the useId hook in a form component:

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

In this example, useId generates a unique ID that links the label to the input, ensuring that screen readers and other assistive technologies can correctly identify the form field relationship.

Unlike useState or useEffect, useId does not accept any arguments and returns a single string value. There's no setter or updater function because the ID it provides is meant to be constant and unique throughout the component's lifecycle.

It's especially useful in server-side rendering (SSR) contexts because it ensures consistency between server-generated IDs and client-side generated ones, avoiding hydration mismatches.

Remember, the main use of useId is for accessibility and managing relationships between different DOM elements, like labels and inputs. It helps keep your UI predictable and accessible without having to manage unique IDs yourself.

One important thing to call out is that you should never use useId to generate IDs for non-DOM elements, like keys in a list or unique keys for React elements. Those IDs should come from your data, not from useId.

📜 Check the useId docs for more info. (There's this interesting identifierPrefix feature you'll probably never use too! 😅)