Form Validation for Handling Expected Errors

We operate under a golden rule in web development: never trust the client. While client-side validation offers quick feedback, it can always be bypassed. A malicious user could disable JavaScript or send a direct request to our server endpoint, skipping our front-end checks entirely. True data integrity and security come from validating everything on the server.

In this lesson, we’ll strengthen our Server Action form submissions with server-side validation to ensure the data we receive is trustworthy.

Implementing validation in Server Actions

Let’s start with the kinds of issues we can predict: expected errors. While we could write a series of if/else checks to validate each input, a more scalable approach is to use a schema-based library. We’ll use Zod, which works well with TypeScript and provides a straightforward way to define data shapes.

Our strategy is to validate the incoming form data inside the Server Action. If validation fails, we won’t throw an error. Instead, we’ll catch the validation issues and return a structured JSON object containing the error messages for each specific field. This gives our Client Component the ...