TypeScript in Next.js

Module 17 — TypeScript in Next.js

TypeScript is an essential part of modern Next.js development.

Next.js supports TypeScript directly, allowing you to add static types to:

• Components
• Props
• API responses
• Server functions
• Client functions
• Database results
• Forms
• Route parameters
• Service functions
• Async operations

A good TypeScript architecture catches many mistakes before your application runs.

The basic idea is:

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1JavaScript
2    ↓
3Add Types
4    ↓
5TypeScript
6    ↓
7Compile-time Safety
8    ↓
9More Reliable Next.js Application

Why TypeScript Matters in Next.js

Consider a JavaScript object:

tsxCopy
1const course = {
2  id: "101",
3  title: "Next.js",
4  price: 499,
5};

You know what the object contains, but TypeScript can make that structure explicit.

tsxCopy
1type Course = {
2  id: string;
3  title: string;
4  price: number;
5};

Now:

tsxCopy
1const course: Course = {
2  id: "101",
3  title: "Next.js",
4  price: 499,
5};

If you accidentally write:

tsxCopy
1const course: Course = {
2  id: "101",
3  title: "Next.js",
4  price: "499",
5};

TypeScript reports an error because:

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1Expected:
2number
3
4Received:
5string

This is especially useful in large Next.js applications where data moves through many layers.

TypeScript and Next.js Architecture

A real application may have this flow:

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1Database
2    ↓
3Backend API
4    ↓
5API Response
6    ↓
7Service Function
8    ↓
9Server Component
10    ↓
11Client Component

TypeScript can define the structure at every stage:

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1Database Result
2      ↓
3Course Type
4      ↓
5API Response Type
6      ↓
7Service Return Type
8      ↓
9Component Props

This makes data flow much easier to understand.

1. Type Aliases

A type alias defines the structure of a value.

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1type Course = {
2  id: string;
3  title: string;
4  description: string;
5  price: number;
6};

Now you can use it:

tsCopy
1const course: Course = {
2  id: "101",
3  title: "Next.js",
4  description: "Learn Next.js",
5  price: 499,
6};

This is one of the most common TypeScript patterns in Next.js.

Type Aliases for Component Props

Suppose a component receives a course:

tsxCopy
1type Course = {
2  id: string;
3  title: string;
4  price: number;
5};
6
7type CourseCardProps = {
8  course: Course;
9};
10
11export function CourseCard({
12  course,
13}: CourseCardProps) {
14  return (
15    <article>
16      <h2>{course.title}</h2>
17      <p>₹{course.price}</p>
18    </article>
19  );
20}

Now the component knows exactly what it expects.

2. Interfaces

Interfaces can also describe object structures.

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1interface Course {
2  id: string;
3  title: string;
4  description: string;
5  price: number;
6}

You can use it exactly like a type:

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1const course: Course = {
2  id: "101",
3  title: "Next.js",
4  description: "Learn Next.js",
5  price: 499,
6};

Type vs Interface

Both are useful.

For example:

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1type Course = {
2  id: string;
3  title: string;
4};

and:

tsCopy
1interface Course {
2  id: string;
3  title: string;
4}

are both valid ways to describe an object.

A practical approach is to use either consistently across your project.

Type aliases are particularly convenient for:

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1Union types
2Primitive aliases
3Tuples
4Mapped types
5Combinations of types

Interfaces are useful when modeling extendable object contracts.

3. Extending Interfaces

Interfaces can extend other interfaces.

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1interface BaseEntity {
2  id: string;
3  createdAt: string;
4}
5
6interface Course extends BaseEntity {
7  title: string;
8  price: number;
9}

Now Course contains:

textCopy
1id
2createdAt
3title
4price

Example:

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1const course: Course = {
2  id: "101",
3  createdAt: "2026-08-23",
4  title: "Next.js",
5  price: 499,
6};

4. Generics

Generics allow you to write reusable code that works with different types.

A simple example:

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1function identity<T>(value: T): T {
2  return value;
3}

Now TypeScript can infer the type:

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1const name = identity("Ankit");

Here:

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1T = string

Another example:

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1const number = identity(100);

Here:

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1T = number

The same function works with both.

Generic API Responses

Generics become extremely useful when building API clients.

Define:

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1type ApiResponse<T> = {
2  data: T;
3  message: string;
4  success: boolean;
5};

Now you can create:

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1type Course = {
2  id: string;
3  title: string;
4};

Then:

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1type CourseResponse =
2  ApiResponse<Course>;

And:

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1type CourseListResponse =
2  ApiResponse<Course[]>;

The generic structure remains the same while the data type changes.

5. Function Types

You can explicitly define the type of a function.

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1type Add = (
2  a: number,
3  b: number
4) => number;

Then:

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1const add: Add = (
2  a,
3  b
4) => {
5  return a + b;
6};

TypeScript knows:

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1a → number
2b → number
3return → number

Function Types in Next.js

Function types are useful for:

• Event handlers
• Service functions
• Callbacks
• API functions
• Utility functions

For example:

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1type GetCourse = (
2  slug: string
3) => Promise<Course>;

Then:

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1const getCourse: GetCourse =
2  async (slug) => {
3    // Fetch course
4  };

6. API Response Types

API responses should ideally have explicit types.

Suppose your API returns:

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1{
2  "id": "101",
3  "title": "Next.js",
4  "price": 499
5}

Create:

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1type Course = {
2  id: string;
3  title: string;
4  price: number;
5};

Then:

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1async function getCourse(
2  slug: string
3): Promise<Course> {
4  const response = await fetch(
5    `/api/courses/${slug}`
6  );
7
8  if (!response.ok) {
9    throw new Error(
10      "Failed to fetch course"
11    );
12  }
13
14  return response.json();
15}

Now the function promises:

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1Promise<Course>

7. Generic API Client

A reusable API client can use generics.

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1async function apiFetch<T>(
2  url: string
3): Promise<T> {
4  const response = await fetch(url);
5
6  if (!response.ok) {
7    throw new Error(
8      "API request failed"
9    );
10  }
11
12  return response.json();
13}

Now:

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1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );

And:

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1const courses =
2  await apiFetch<Course[]>(
3    "/api/courses"
4  );

The same function works for both:

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1apiFetch<Course>()
2       ↓
3Course
4
5apiFetch<Course[]>()
6       ↓
7Course[]

8. Component Props

Props should be typed.

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1type ButtonProps = {
2  title: string;
3  disabled?: boolean;
4};
5
6export function Button({
7  title,
8  disabled = false,
9}: ButtonProps) {
10  return (
11    <button disabled={disabled}>
12      {title}
13    </button>
14  );
15}

Usage:

tsxCopy
1<Button
2  title="Save"
3  disabled={false}
4/>

TypeScript prevents incorrect values such as:

tsxCopy
1<Button
2  title={123}
3/>

because title expects a string.

9. Optional Properties

A property can be optional using ?.

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1type User = {
2  id: string;
3  name: string;
4  avatar?: string;
5};

Now both are valid:

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1const user1: User = {
2  id: "1",
3  name: "Ankit",
4};

and:

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1const user2: User = {
2  id: "2",
3  name: "Rahul",
4  avatar: "/avatar.png",
5};

The avatar property is optional.

Optional Props in React Components

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1type CardProps = {
2  title: string;
3  description?: string;
4};
5
6export function Card({
7  title,
8  description,
9}: CardProps) {
10  return (
11    <article>
12      <h2>{title}</h2>
13
14      {description && (
15        <p>{description}</p>
16      )}
17    </article>
18  );
19}

Now:

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1<Card title="Next.js" />

is valid.

And:

tsxCopy
1<Card
2  title="Next.js"
3  description="Learn Next.js"
4/>

is also valid.

10. Union Types

A union allows a value to have one of several types.

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1type Status =
2  | "loading"
3  | "success"
4  | "error";

Now:

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1let status: Status;
2
3status = "loading";
4status = "success";
5status = "error";

But:

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1status = "completed";

is invalid.

Union Types for API States

This is very useful for UI state:

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1type RequestState =
2  | "idle"
3  | "loading"
4  | "success"
5  | "error";

A component can use:

tsxCopy
1const [status, setStatus] =
2  useState<RequestState>("idle");

Now the state cannot accidentally become an unrelated value.

Discriminated Unions

For more advanced API states:

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1type Result<T> =
2  | {
3      success: true;
4      data: T;
5    }
6  | {
7      success: false;
8      error: string;
9    };

Now:

tsCopy
1function handleResult(
2  result: Result<Course>
3) {
4  if (result.success) {
5    console.log(
6      result.data.title
7    );
8  } else {
9    console.error(
10      result.error
11    );
12  }
13}

TypeScript understands which properties are available based on success.

11. Utility Types

TypeScript provides built-in utility types for transforming existing types.

Common utilities include:

textCopy
1Partial
2Required
3Pick
4Omit
5Record
6Readonly
7ReturnType
8Parameters
9Awaited

These are extremely useful in Next.js applications.

Partial

Suppose:

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1type Course = {
2  id: string;
3  title: string;
4  price: number;
5};

For an update operation, you may not need every field.

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1type UpdateCourse =
2  Partial<Course>;

Now all properties are optional:

tsCopy
1const update: UpdateCourse = {
2  title: "Advanced Next.js",
3};

This is useful for PATCH APIs.

Pick

Pick selects specific properties.

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1type CoursePreview =
2  Pick<Course, "id" | "title">;

Now:

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1const preview: CoursePreview = {
2  id: "101",
3  title: "Next.js",
4};

The preview does not need:

textCopy
1price

or other course fields.

Omit

Omit removes properties.

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1type PublicCourse =
2  Omit<Course, "price">;

This can be useful when creating a public representation of a type.

Record

Record is useful for dictionaries/maps.

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1type CourseMap =
2  Record<string, Course>;

Example:

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1const courses: CourseMap = {
2  nextjs: {
3    id: "1",
4    title: "Next.js",
5    price: 499,
6  },
7};

Readonly

Readonly prevents modification through that type.

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1type ReadonlyCourse =
2  Readonly<Course>;

This is useful when a function should only consume data.

ReturnType

You can derive the return type of a function.

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1function getCourse() {
2  return {
3    id: "1",
4    title: "Next.js",
5  };
6}
7
8type Course =
9  ReturnType<typeof getCourse>;

Now TypeScript derives the type automatically.

Awaited

For asynchronous functions:

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1async function getCourse() {
2  return {
3    id: "1",
4    title: "Next.js",
5  };
6}

You can extract the resolved value:

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1type Course =
2  Awaited<
3    ReturnType<typeof getCourse>
4  >;

This is useful for complex service architectures.

12. Async Function Types

An asynchronous function usually returns a Promise.

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1type GetCourse = (
2  slug: string
3) => Promise<Course>;

Implementation:

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1const getCourse: GetCourse =
2  async (slug) => {
3    const response =
4      await fetch(
5        `/api/courses/${slug}`
6      );
7
8    return response.json();
9  };

The important concept is:

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1Normal function
2↓
3Course
4
5Async function
6↓
7Promise<Course>

Async Service Functions

A typical Next.js service:

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1type Course = {
2  id: string;
3  title: string;
4  description: string;
5};
6
7export async function getCourse(
8  slug: string
9): Promise<Course> {
10  const response =
11    await fetch(
12      `/api/courses/${slug}`
13    );
14
15  if (!response.ok) {
16    throw new Error(
17      "Course request failed"
18    );
19  }
20
21  return response.json();
22}

Now every caller knows:

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1getCourse()
2      ↓
3Promise<Course>

13. Generic Service Function

Now combine generics and async functions.

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1async function apiFetch<T>(
2  url: string
3): Promise<T> {
4  const response =
5    await fetch(url);
6
7  if (!response.ok) {
8    throw new Error(
9      "API request failed"
10    );
11  }
12
13  return response.json();
14}

Use it:

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1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );

Or:

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1const courses =
2  await apiFetch<Course[]>(
3    "/api/courses"
4  );

This gives you a reusable typed API layer.

14. Generic API Response

A production API may return:

jsonCopy
1{
2  "success": true,
3  "data": {
4    "id": "101",
5    "title": "Next.js"
6  }
7}

Define:

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1type ApiResponse<T> = {
2  success: boolean;
3  data: T;
4};

Then:

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1type CourseResponse =
2  ApiResponse<Course>;

And:

tsCopy
1type CoursesResponse =
2  ApiResponse<Course[]>;

Now:

tsCopy
1async function apiFetch<T>(
2  url: string
3): Promise<ApiResponse<T>> {
4  const response =
5    await fetch(url);
6
7  if (!response.ok) {
8    throw new Error(
9      "API request failed"
10    );
11  }
12
13  return response.json();
14}

Usage:

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1const response =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );
5
6console.log(
7  response.data.title
8);

15. Generic Function Schema

The basic generic function pattern is:

tsCopy
1function functionName<T>(
2  value: T
3): T {
4  return value;
5}

For an asynchronous API function:

tsCopy
1async function apiFetch<T>(
2  url: string
3): Promise<T> {
4  const response =
5    await fetch(url);
6
7  return response.json();
8}

The important structure is:

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1<T>
2 ↓
3Generic input type
4
5Promise<T>
6 ↓
7Generic async return type

16. Advanced Function Design

A reusable API client can be designed like this:

tsCopy
1async function apiFetch<
2  T,
3  TError = string
4>(
5  url: string,
6  options?: RequestInit
7): Promise<T> {
8  const response =
9    await fetch(
10      url,
11      options
12    );
13
14  if (!response.ok) {
15    throw new Error(
16      `Request failed: ${response.status}`
17    );
18  }
19
20  return response.json();
21}

Now you can specify the expected result:

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1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );

Or:

tsCopy
1const courses =
2  await apiFetch<Course[]>(
3    "/api/courses"
4  );

The function remains reusable.

17. Generic Functions With Arrays

A generic function can also work with arrays.

tsCopy
1function first<T>(
2  items: T[]
3): T | undefined {
4  return items[0];
5}

Usage:

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1const course =
2  first<Course>(courses);

TypeScript understands that:

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1Course[]
2   ↓
3first()
4   ↓
5Course | undefined

18. Generic API Client With HTTP Methods

A more realistic API client:

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1async function apiFetch<T>(
2  url: string,
3  options?: RequestInit
4): Promise<T> {
5  const response =
6    await fetch(url, {
7      ...options,
8      headers: {
9        "Content-Type":
10          "application/json",
11        ...options?.headers,
12      },
13    });
14
15  if (!response.ok) {
16    throw new Error(
17      `HTTP ${response.status}`
18    );
19  }
20
21  return response.json();
22}

Now:

GET

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1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );

POST

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1const course =
2  await apiFetch<Course>(
3    "/api/courses",
4    {
5      method: "POST",
6      body: JSON.stringify({
7        title: "Next.js",
8      }),
9    }
10  );

PATCH

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1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs",
4    {
5      method: "PATCH",
6      body: JSON.stringify({
7        title: "Advanced Next.js",
8      }),
9    }
10  );

The same generic function supports multiple API operations.

19. Typing Route Parameters

Next.js dynamic routes can also be typed.

For:

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1app/courses/[slug]/page.tsx

you can write:

tsxCopy
1type PageProps = {
2  params: Promise<{
3    slug: string;
4  }>;
5};
6
7export default async function CoursePage({
8  params,
9}: PageProps) {
10  const { slug } = await params;
11
12  return (
13    <h1>
14      Course: {slug}
15    </h1>
16  );
17}

Now the route structure and TypeScript structure agree:

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1[courses]
2    ↓
3[slug]
4    ↓
5string

20. Typing Search Parameters

Search parameters can also be typed.

tsxCopy
1type PageProps = {
2  searchParams: Promise<{
3    page?: string;
4    category?: string;
5  }>;
6};
7
8export default async function CoursesPage({
9  searchParams,
10}: PageProps) {
11  const params =
12    await searchParams;
13
14  const page =
15    params.page ?? "1";
16
17  const category =
18    params.category;
19
20  return (
21    <div>
22      Page: {page}
23
24      {category && (
25        <p>
26          Category: {category}
27        </p>
28      )}
29    </div>
30  );
31}

Optional properties are appropriate because query parameters may not exist.

21. Typing Children

React components often receive children.

tsxCopy
1import type { ReactNode } from "react";
2
3type LayoutProps = {
4  children: ReactNode;
5};
6
7export function Layout({
8  children,
9}: LayoutProps) {
10  return (
11    <main>
12      {children}
13    </main>
14  );
15}

Now the component accepts React content safely.

22. Typing Event Handlers

Client Components often use event handlers.

tsxCopy
1"use client";
2
3import type {
4  ChangeEvent,
5} from "react";
6
7export function SearchBox() {
8  function handleChange(
9    event: ChangeEvent<HTMLInputElement>
10  ) {
11    console.log(
12      event.target.value
13    );
14  }
15
16  return (
17    <input
18      onChange={handleChange}
19    />
20  );
21}

TypeScript knows:

textCopy
1event
2 ↓
3ChangeEvent<HTMLInputElement>
4 ↓
5event.target
6 ↓
7HTMLInputElement

23. Typing Form Submission

tsxCopy
1"use client";
2
3import type {
4  FormEvent,
5} from "react";
6
7export function CourseForm() {
8  function handleSubmit(
9    event: FormEvent<HTMLFormElement>
10  ) {
11    event.preventDefault();
12
13    const form =
14      new FormData(
15        event.currentTarget
16      );
17
18    console.log(
19      form.get("title")
20    );
21  }
22
23  return (
24    <form onSubmit={handleSubmit}>
25      <input name="title" />
26
27      <button type="submit">
28        Create
29      </button>
30    </form>
31  );
32}

This gives you type safety for browser events.

24. Avoid any

One of the most important TypeScript rules is:

Avoid using any unless there is a very specific reason.

Bad:

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1function getCourse(
2  data: any
3) {
4  return data.title;
5}

Now TypeScript cannot protect you.

Better:

tsCopy
1type Course = {
2  id: string;
3  title: string;
4};
5
6function getCourse(
7  data: Course
8) {
9  return data.title;
10}

Now invalid data is much easier to detect.

25. unknown vs any

When you genuinely don't know the type of external data, unknown is safer.

tsCopy
1function processData(
2  data: unknown
3) {
4  // Validate before using
5}

For example:

tsCopy
1function isCourse(
2  value: unknown
3): value is Course {
4  if (
5    typeof value !== "object" ||
6    value === null
7  ) {
8    return false;
9  }
10
11  return (
12    "id" in value &&
13    "title" in value
14  );
15}

Then:

tsCopy
1if (isCourse(data)) {
2  console.log(data.title);
3}

This is much safer than blindly using any.

26. TypeScript Does Not Validate Runtime Data

This is extremely important.

TypeScript types disappear at runtime.

For example:

tsCopy
1type Course = {
2  title: string;
3};

does not automatically validate API data.

An external API could still return:

jsonCopy
1{
2  "title": 123
3}

Therefore:

textCopy
1TypeScript
2    ↓
3Compile-time safety

while runtime validation requires tools or explicit checks:

textCopy
1API Response
2    ↓
3Runtime Validation
4    ↓
5TypeScript-safe Data

Libraries such as Zod are commonly used for this purpose.

27. TypeScript + Zod

You can define a runtime schema:

tsCopy
1import { z } from "zod";
2
3const courseSchema = z.object({
4  id: z.string(),
5  title: z.string(),
6  price: z.number(),
7});

Then validate API data:

tsCopy
1const data =
2  await response.json();
3
4const course =
5  courseSchema.parse(data);

Now you have:

textCopy
1External Data
2      ↓
3Zod Validation
4      ↓
5Validated Course
6      ↓
7Application

This creates a stronger boundary around external data.

28. Complete Typed Service Architecture

Let's combine everything.

Course type

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1export type Course = {
2  id: string;
3  slug: string;
4  title: string;
5  description: string;
6  price: number;
7};

Generic API client

tsCopy
1export async function apiFetch<T>(
2  url: string,
3  options?: RequestInit
4): Promise<T> {
5  const response =
6    await fetch(url, options);
7
8  if (!response.ok) {
9    throw new Error(
10      `API request failed: ${response.status}`
11    );
12  }
13
14  return response.json();
15}

Course service

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1import type { Course } from "@/types/course";
2import { apiFetch } from "@/lib/api";
3
4export function getCourse(
5  slug: string
6): Promise<Course> {
7  return apiFetch<Course>(
8    `/api/courses/${slug}`
9  );
10}

Server Component

tsxCopy
1import { getCourse } from "@/services/course.service";
2
3export default async function CoursePage({
4  params,
5}: {
6  params: Promise<{
7    slug: string;
8  }>;
9}) {
10  const { slug } = await params;
11
12  const course =
13    await getCourse(slug);
14
15  return (
16    <article>
17      <h1>{course.title}</h1>
18
19      <p>
20        {course.description}
21      </p>
22
23      <strong>
24        ₹{course.price}
25      </strong>
26    </article>
27  );
28}

The complete type-safe architecture is:

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1Course Type
2     ↓
3Generic API Client
4     ↓
5Course Service
6     ↓
7Server Component
8     ↓
9UI

29. Advanced Function Design

The function design from this module can be summarized as:

tsCopy
1async function apiFetch<
2  T
3>(
4  url: string,
5  options?: RequestInit
6): Promise<T> {
7  const response =
8    await fetch(
9      url,
10      options
11    );
12
13  if (!response.ok) {
14    throw new Error(
15      `Request failed: ${response.status}`
16    );
17  }
18
19  return response.json();
20}

Usage:

tsCopy
1const course =
2  await apiFetch<Course>(
3    "/api/courses/nextjs"
4  );

tsCopy
1const courses =
2  await apiFetch<Course[]>(
3    "/api/courses"
4  );

The important pattern is:

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1<T>
2 ↓
3Caller specifies expected type
4
5Promise<T>
6 ↓
7Async function returns that type

This pattern is extremely common in professional TypeScript codebases.

30. TypeScript Mental Model

Think about TypeScript as a contract system.

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1             TypeScript
2                  │
3       ┌──────────┼──────────┐
4       ▼          ▼          ▼
5     Props      API        Functions
6       │          │          │
7       ▼          ▼          ▼
8     Types      Types      Types
9       │          │          │
10       └──────────┼──────────┘
11                  ▼
12            Safer Application

When data moves through your application:

textCopy
1API
2 ↓
3Course
4 ↓
5Service
6 ↓
7Page
8 ↓
9Component
10 ↓
11Props

the types document what each layer expects.

Common TypeScript Mistakes in Next.js

Mistake 1 — Using any everywhere

tsCopy
1const data: any = ...

This removes much of TypeScript's value.

Mistake 2 — Assuming API data is automatically safe

tsCopy
1const course: Course =
2  await response.json();

The annotation does not validate the runtime response.

Use runtime validation for untrusted external data.

Mistake 3 — Huge duplicated types

Avoid redefining the same structure in many files.

Instead:

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1types/
2├── course.ts
3├── user.ts
4├── project.ts
5└── api.ts

Reuse shared types.

Mistake 4 — Overcomplicated generics

Generics are powerful, but don't introduce them when a simple type is enough.

Simple:

tsCopy
1function getCourse():
2  Promise<Course>

Use generics when you genuinely need reusable behavior:

tsCopy
1function apiFetch<T>():
2  Promise<T>

Mistake 5 — Confusing compile-time and runtime validation

Remember:

textCopy
1TypeScript
2     ↓
3Compile time
4
5Zod / validation
6     ↓
7Runtime

For external APIs, runtime validation may be necessary.

Final TypeScript Architecture

A strong Next.js TypeScript application can follow:

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1                    TypeScript
2                        │
3          ┌─────────────┼─────────────┐
4          ▼             ▼             ▼
5       Components     Services       APIs
6          │             │             │
7        Props        Functions      Responses
8          │             │             │
9          └─────────────┼─────────────┘
10                        ▼
11                  Shared Types
12                        │
13                        ▼
14                 Safer Data Flow

For a real course application:

textCopy
1PostgreSQL
2    ↓
3Django / Node.js
4    ↓
5API Response
6    ↓
7Course Type
8    ↓
9Generic API Client
10    ↓
11Course Service
12    ↓
13Next.js Server Component
14    ↓
15Typed Component Props
16    ↓
17UI

The key idea is:

Use TypeScript to make the contracts between your database, APIs, services, pages, and components explicit.

Once you understand types, interfaces, generics, function types, API response types, utility types, and async function types, you can build much larger Next.js applications with significantly better maintainability and developer safety.

Module 17 Learning Checklist

After completing this module, you should understand:

• Type aliases
• Interfaces
• Interface inheritance
• Generics
• Function types
• Async function types
• Component props
• Optional properties
• Union types
• Discriminated unions
• API response types
• Generic API clients
• Utility types
• Partial
• Pick
• Omit
• Record
• Readonly
• ReturnType
• Awaited
• Typed route parameters
• Typed search parameters
• Typed React events
• any vs unknown
• Runtime validation
• TypeScript with Zod
• Type-safe service architecture