test.data.ts

export const mockedCorrectUser = {
  name: "abc",
  uuid: "b3963682-08f1-4946-b832-3b7fe4d45f6c",
  email: "me@awesome.com",
  verified: true,
};

export const invalidUser = {
  name: "abc",
  uuid: "abc",
  email: "me",
};

export const invalidUserUuid = {
  name: "abc",
  uuid: "abc",
  email: "me@example.com",
  verified: true,
};

export const logIsUser = (user: any, isUser: (user: any) => boolean) => {
  console.log(`Assert Passed data object is a User ? ${isUser(user)}`);
};

typeguard.ts

import {
  invalidUser,
  invalidUserUuid,
  logIsUser,
  mockedCorrectUser,
} from "./test_data";

interface User {
  name: string;
  email: string;
  uuid: string;
  verified: boolean;
}

const isUuidV4 = (uuid: string) => {
  return /^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i.test(
    uuid
  );
};

const isUser = (obj: any): obj is User => {
  if (!obj?.name || typeof obj.name !== "string") {
    return false;
  }
  if (!obj?.email || typeof obj.email !== "string") {
    return false;
  }
  if (!obj?.uuid || typeof obj.uuid !== "string" || !isUuidV4(obj.uuid)) {
    return false;
  }
  if (!obj?.verified || typeof obj.verified !== "boolean") {
    return false;
  }
  return true;
};

logIsUser(mockedCorrectUser, isUser);
logIsUser(invalidUser, isUser);
logIsUser(invalidUserUuid, isUser);

typeguard.zod.ts

import z from "zod";
import {
  invalidUser,
  invalidUserUuid,
  logIsUser,
  mockedCorrectUser,
} from "./test_data";

const userSchema = z.object({
  uuid: z.string().uuid(),
  name: z.string().optional(),
  email: z.string().email(),
  verified: z.boolean().default(false),
});

type User = z.infer<typeof userSchema>;

const isUser = (obj: any): obj is User => {
  if (!userSchema.safeParse(obj).success) {
    return false;
  }
  return true;
};

logIsUser(mockedCorrectUser, isUser);
logIsUser(invalidUser, isUser);
logIsUser(invalidUserUuid, isUser);