Schema definition in NextJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Next.js schema validation?

Given this Next.js schema using Zod, what will be the result of validating { age: 20 }?

NextJS

import { z } from 'zod';

const userSchema = z.object({
  name: z.string().min(1),
  age: z.number().int().min(18),
});

const result = userSchema.safeParse({ age: 20 });
console.log(result.success);

A Throws a runtime error

B true

C false

D undefined

💡 Hint

Check if all required fields are present in the object.

The schema requires both name and age. Since name is missing, validation fails and result.success is false.

📝 Syntax

intermediate

Which option correctly defines a Next.js schema for a user with optional email?

Choose the correct Zod schema that defines a user object with a required username string and an optional email string.

A z.object({ username: z.string().optional(), email: z.string() })

B z.object({ username: z.string().required(), email: z.string() })

C z.object({ username: z.string(), email: z.string().nullable() })

D z.object({ username: z.string(), email: z.string().optional() })

💡 Hint

Optional fields use the .optional() method in Zod.

Option D correctly marks email as optional. Option D makes username optional which is wrong. Option D allows email to be null but not missing. Option D uses .required() which is not a Zod method.

🔧 Debug

advanced

Why does this Next.js schema validation throw an error?

Examine the code and identify why validation throws an error instead of returning a result.

NextJS

import { z } from 'zod';

const productSchema = z.object({
  id: z.number(),
  price: z.number().positive(),
});

const data = { id: 1, price: -5 };

const result = productSchema.parse(data);
console.log(result);

A Because price is negative and parse throws on invalid data

B Because id is not a string

C Because parse returns undefined on failure

D Because the schema is missing a required field

💡 Hint

Check the value constraints on the price field.

The price field must be positive. Since -5 is negative, parse throws an error instead of returning a result.

❓ state_output

advanced

What is the value of isValid after this Next.js schema check?

Given this code, what is the value of isValid after validation?

NextJS

import { z } from 'zod';

const loginSchema = z.object({
  email: z.string().email(),
  password: z.string().min(8),
});

const input = { email: '[e-mail]', password: '1234567' };

const isValid = loginSchema.safeParse(input).success;

A true

B false

C Throws a TypeError

D undefined

💡 Hint

Check the minimum length required for password.

The password is only 7 characters but the schema requires at least 8, so validation fails and isValid is false.

🧠 Conceptual

expert

Which statement about Next.js schema definitions with Zod is correct?

Select the only true statement about using Zod schemas in Next.js for data validation.

A Zod schemas can be used both server-side and client-side for consistent validation.

B Zod schemas can only validate client-side data, not server-side.

C Zod automatically converts all input data types to strings during validation.

D Zod schemas require manual error handling for every validation failure.

💡 Hint

Think about where Next.js code runs and how Zod works.

Zod schemas are JavaScript objects and can be used anywhere JavaScript runs, including both server and client in Next.js, ensuring consistent validation.

Practice

1. What is the main purpose of schema definition in a Next.js project?

easy

A. To manage server-side rendering

B. To describe the shape and rules of your data

C. To style the user interface components

D. To handle routing between pages

Solution

1. Step 1: Understand schema definition role

   Schema definition is about specifying how data should look and behave.

2. Step 2: Identify its main use in Next.js

   It helps validate data to catch errors early before using it in the app.

3. Final Answer:

   To describe the shape and rules of your data -> Option B

4. Quick Check:

   Schema = Data shape and rules [OK]

Hint: Schema defines data shape and validation rules [OK]

Common Mistakes:

• Confusing schema with UI styling
• Thinking schema manages routing
• Assuming schema handles rendering

2. Which of the following is the correct way to define a simple string schema using the zod library in Next.js?

easy

A. const schema = z.string();

B. const schema = z.string;

C. const schema = z.String();

D. const schema = new z.string();

Solution

1. Step 1: Recall zod syntax for string schema

   In zod, string schema is created by calling z.string() as a function.

2. Step 2: Check each option's syntax

   const schema = z.string(); uses z.string() correctly. Others miss parentheses or use wrong casing or new keyword.

3. Final Answer:

   const schema = z.string(); -> Option A

4. Quick Check:

   z.string() is correct syntax [OK]

Hint: Use parentheses to call z.string() function [OK]

Common Mistakes:

• Omitting parentheses after z.string
• Using uppercase 'String' instead of 'string'
• Using 'new' keyword incorrectly

3. Given this schema definition using zod:

const userSchema = z.object({
  name: z.string(),
  age: z.number().min(18)
});
const result = userSchema.safeParse({ name: "Alice", age: 16 });
console.log(result.success);

What will be logged to the console?

medium

A. true

B. Throws an error

C. false

D. undefined

Solution

1. Step 1: Understand schema rules

   The schema requires 'name' as string and 'age' as number at least 18.

2. Step 2: Check input data against schema

   Input has age 16, which is less than minimum 18, so validation fails.

3. Final Answer:

   false -> Option C

4. Quick Check:

   Validation fails because age < 18 [OK]

Hint: Check min() constraints carefully in validation [OK]

Common Mistakes:

• Assuming validation passes despite age < 18
• Confusing safeParse result with direct parse
• Expecting an error instead of false success

4. Identify the error in this Next.js schema definition using zod:

const productSchema = z.object({
  id: z.number,
  title: z.string(),
  price: z.number()
});

medium

A. Missing comma after 'title' property

B. Schema object should be an array

C. Using z.string() incorrectly

D. Missing parentheses after z.number for 'id'

Solution

1. Step 1: Check each property schema syntax

   'id' uses z.number without parentheses, which is incorrect syntax.

2. Step 2: Verify other properties and object structure

   Other properties are correct; object schema is correctly defined as an object, not array.

3. Final Answer:

   Missing parentheses after z.number for 'id' -> Option D

4. Quick Check:

   z.number() needs parentheses [OK]

Hint: Always call zod types as functions with () [OK]

Common Mistakes:

• Forgetting parentheses after z.number or z.string
• Thinking schema must be an array
• Missing commas between properties

5. You want to define a schema for a user profile in Next.js using zod where the 'email' field is optional but if present must be a valid email string. Which schema definition is correct?

hard

A. const userProfileSchema = z.object({ email: z.string().email().optional() });

B. const userProfileSchema = z.object({ email: z.optional(z.string().email) });

C. const userProfileSchema = z.object({ email: z.string().optional().email() });

D. const userProfileSchema = z.object({ email: z.string().email() || undefined });

Solution

1. Step 1: Understand optional email schema in zod

   To make a field optional but validate if present, use .optional() after .email().

2. Step 2: Check each option's method chaining

   const userProfileSchema = z.object({ email: z.string().email().optional() }); correctly chains z.string().email().optional(). const userProfileSchema = z.object({ email: z.optional(z.string().email) }); uses z.optional incorrectly. const userProfileSchema = z.object({ email: z.string().optional().email() }); calls optional before email, which breaks validation. const userProfileSchema = z.object({ email: z.string().email() || undefined }); uses invalid syntax.

3. Final Answer:

   const userProfileSchema = z.object({ email: z.string().email().optional() }); -> Option A

4. Quick Check:

   Use .optional() after .email() for optional validated fields [OK]

Hint: Chain .optional() after .email() for optional email fields [OK]

Common Mistakes:

• Placing .optional() before .email()
• Using z.optional() wrapper incorrectly
• Trying to use || undefined for optional