zod

TITLE: Overwrite Transformations Retaining Schema Type in Zod 4 DESCRIPTION: Introduces the new .overwrite() method in Zod v4, designed for transformations that do not change the inferred type. This method returns an instance of the original schema class, allowing continued method chaining and retaining introspectability. SOURCE: https://zod.dev/v4/v4

LANGUAGE: TypeScript CODE:

z.number().overwrite(val => val ** 2).max(100);
// => ZodNumber

---

TITLE: Compose Discriminated Unions in Zod 4 DESCRIPTION: Demonstrates the new ability in Zod v4 to use one discriminated union schema (MyErrors) as a member within another discriminated union (MyResult), enabling powerful schema composition patterns. SOURCE: https://zod.dev/v4/v4

LANGUAGE: TypeScript CODE:

const BaseError = z.object({ status: z.literal("failed"), message: z.string() });
const MyErrors = z.discriminatedUnion("code", [
  BaseError.extend({ code: z.literal(400) }),
  BaseError.extend({ code: z.literal(401) }),
  BaseError.extend({ code: z.literal(500) })
]);

const MyResult = z.discriminatedUnion("status", [
  z.object({ status: z.literal("success"), data: z.string() }),
  MyErrors
]);

---

TITLE: Defining Synchronous Zod-Validated Functions in Zod v4 DESCRIPTION: Demonstrates the new API for defining Zod-validated functions using z.function() in Zod v4. It shows how to define input and output schemas upfront and implement the function logic synchronously using .implement(). SOURCE: https://zod.dev/v4/v4/changelog

LANGUAGE: TypeScript CODE:

const myFunction = z.function({
  input: [z.object({
    name: z.string(),
    age: z.number().int(),
  })],
  output: z.string(),
});

myFunction.implement((input) => {
  return `Hello ${input.name}, you are ${input.age} years old.`;
});

---

TITLE: Use Top-Level String Format Functions - Zod v4 - JavaScript DESCRIPTION: Lists the various string format validation functions (like email, uuid, url, etc.) that are now available directly as top-level methods on the z module in Zod v4. This change makes them more concise to use and improves tree-shaking. SOURCE: https://zod.dev/v4/v4

LANGUAGE: JavaScript CODE:

z.email();\nz.uuidv4();\nz.uuidv7();\nz.uuidv8();\nz.ipv4();\nz.ipv6();\nz.cidrv4();\nz.cidrv6();\nz.url();\nz.e164();\nz.base64();\nz.base64url();\nz.jwt();\nz.ascii();\nz.utf8();\nz.lowercase();\nz.iso.date();\nz.iso.datetime();\nz.iso.duration();\nz.iso.time();

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TITLE: Zod 4: Using .check() in zod/v4-mini DESCRIPTION: Illustrates the use of the new .check() method available in zod/v4-mini, which allows composing multiple validations and transforms (referred to as 'checks') on a schema. SOURCE: https://zod.dev/v4/v4/changelog

LANGUAGE: TypeScript CODE:

import { z } from "zod/v4-mini";

z.string().check(
  z.minLength(10),
  z.maxLength(100),
  z.toLowerCase(),
  z.trim(),
);

---

TITLE: Customize Required and Invalid Type Errors with Zod 4 DESCRIPTION: Shows how Zod v4 replaces the separate required_error and invalid_type_error parameters with a single error function that receives an issue object, allowing conditional error messages based on the issue type (e.g., invalid_type or required). SOURCE: https://zod.dev/v4/v4

LANGUAGE: TypeScript CODE:

// Zod 3
- z.string({
-   required_error: "This field is required"
-   invalid_type_error: "Not a string",
- });

LANGUAGE: TypeScript CODE:

// Zod 4
+ z.string({ error: (issue) => issue.input === undefined ?
+  "This field is required" :
+  "Not a string"
+ });

---

TITLE: Customize Errors with Function Syntax in Zod 4 DESCRIPTION: Illustrates how Zod v4 replaces the errorMap function with the unified error function for more complex error customization, allowing access to the issue details to return specific messages based on validation failures like too_small. SOURCE: https://zod.dev/v4/v4