Request validation with Zod in Express

Short summary

A practical tutorial on using Zod 4 for request validation in Express applications, covering schema definition with z.email() and z.uuid(), TypeScript type inference via z.infer, and a reusable validate middleware that parses body, query, and params before route handlers execute. It addresses Zod 4 migration notes (deprecated method forms), error formatting with z.flattenError, and common pitfalls like query string coercion and storing parsed data on res.locals to avoid fighting Express's type system.

• •Define Zod 4 schemas for body, query, and params with z.infer type inference for fully typed route handlers
• •Build a reusable validate middleware using safeParse that returns HTTP 400 with structured error details on invalid input
• •Use z.coerce for query string type conversion and store parsed query/params on res.locals to avoid Express type conflicts

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