Leveraging the useId Hook in React: Simplifying Unique ID Generation
Tags: react, hooks, javascript
Published: 2023-07-05 05:18:07

    
The useId hook in React serves the purpose of generating a unique identifier (id). The format of the generated id is a colon followed by the letter 'r', then a number, and finally another colon (e.g., ":r1:", “:r2:”).

You might wonder why we need such an unconventional id format. The reason lies in its uniqueness. When working with inputs and labels, it is considered a best practice to connect them using the label tag. This connection allows for convenient user interaction, especially for checkboxes where clicking on the associated label is easier than clicking on the checkbox itself.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/nsnz3y4qqqdk78eg4ved.png)

However, there are situations where we cannot directly wrap the input with the label tag. In such cases, we can use the htmlFor attribute of the label tag to establish a connection with the input by passing the id of the input element. The challenge then becomes generating a unique id for this purpose.

The useId hook solves this problem by generating a unique and absurd id value. It relieves us of the burden of coming up with meaningful variable names or ids. React's useId hook ensures that the generated id is unique within the component.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/wa6dhn4puvntvymlkvma.png)

Now, let’s address why the useId hook is an integral part of the React ecosystem. One reason is Server Side Rendering (SSR). React can run not only on the client but also on the server. If we were to generate the id using a library like uuid, the id value on the server would differ from the id value on the client. This mismatch would lead to errors and inconsistencies.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/2orksjibjl2t53vomsdq.png)


React’s useId hook solves this issue by providing the same id on both the server and the client during SSR. It achieves this by using a shared treeId as the base id. Note that the id generated by useId is unique only within a component. If multiple useId hooks are used within a component, they will share the same treeId.

The implementation of the useId hook in React involves two functions: mountId and updateId. The former is called when the component is initially rendered or mounted, while the latter is called during subsequent updates. This separation allows for more flexible code without the need for excessive conditional logic.

The mountId function generates an id by combining the treeId and a local counter specific to the current component. This counter increments each time the useId hook is used within the component, ensuring uniqueness within that component.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/dxz0wqi9hi8t1wpcma3g.png)

For Single Page Applications (SPAs), a global counter is used to generate ids across the entire React application. This counter ensures that each useId hook receives a unique id. However, it's important to note that when a component, such as a modal window, is mounted multiple times, a new id will be generated each time. There is no mechanism to retain the previous id.

In conclusion, the useId hook is a valuable tool in React that addresses the need for generating unique ids. Its inclusion in the React ecosystem ensures consistent id generation between the server and client during SSR. The generated ids are non-persistent and unique within a React app. If your project includes multiple React applications, it's recommended to use identifier prefixes to avoid id conflicts.