TypeScript

Preact has first-class TypeScript support with complete type definitions included in the core package. No additional @types packages are needed.

Setup

Preact’s TypeScript definitions are included by default. Just install Preact and start using TypeScript:

Install Preact

npm install preact

Configure TypeScript

Create or update your tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ESNext",
    "jsx": "react-jsx",
    "jsxImportSource": "preact",
    "moduleResolution": "bundler",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true,
    "lib": ["ES2020", "DOM", "DOM.Iterable"]
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Start coding

Create a .tsx file and start building:

import { render } from 'preact';

function App() {
  return <h1>Hello TypeScript!</h1>;
}

render(<App />, document.getElementById('app')!);

Type Definitions

Preact’s type definitions are located in the source code:

src/index.d.ts - Core Preact types
src/jsx.d.ts - JSX type definitions
hooks/src/index.d.ts - Hooks type definitions
compat/src/index.d.ts - React compatibility types

Reference: src/index.d.ts, hooks/src/index.d.ts

Component Types

Function Components
Class Components

Function components are typed using the FunctionComponent type:

import { FunctionComponent } from 'preact';

interface Props {
  name: string;
  age?: number;
}

const Greeting: FunctionComponent<Props> = ({ name, age }) => {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      {age && <p>Age: {age}</p>}
    </div>
  );
};

Or use the shorthand (recommended):

interface Props {
  name: string;
  age?: number;
}

function Greeting({ name, age }: Props) {
  return (
    <div>
      <h1>Hello, {name}!</h1>
      {age && <p>Age: {age}</p>}
    </div>
  );
}

Class components extend Component with props and state types:

import { Component } from 'preact';

interface Props {
  initialCount: number;
}

interface State {
  count: number;
}

class Counter extends Component<Props, State> {
  state: State = {
    count: this.props.initialCount
  };

  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

Props with Children

The ComponentChildren type represents valid children:

import { ComponentChildren } from 'preact';

interface Props {
  title: string;
  children: ComponentChildren;
}

function Card({ title, children }: Props) {
  return (
    <div className="card">
      <h2>{title}</h2>
      <div>{children}</div>
    </div>
  );
}

Alternatively, use FunctionComponent which includes children automatically:

import { FunctionComponent } from 'preact';

interface Props {
  title: string;
}

// children is available automatically
const Card: FunctionComponent<Props> = ({ title, children }) => (
  <div className="card">
    <h2>{title}</h2>
    <div>{children}</div>
  </div>
);

Hooks with TypeScript

import { useState } from 'preact/hooks';

// Type is inferred
function Counter() {
  const [count, setCount] = useState(0);
  // count: number, setCount: (value: number) => void
  
  return (
    <button onClick={() => setCount(count + 1)}>
      Count: {count}
    </button>
  );
}

// Explicit type
interface User {
  name: string;
  email: string;
}

function UserProfile() {
  const [user, setUser] = useState<User | null>(null);
  
  return (
    <div>
      {user ? <p>{user.name}</p> : <p>Loading...</p>}
    </div>
  );
}

Event Handlers

Preact provides specific event types for all DOM events:

import { JSX } from 'preact';

function Form() {
  const handleSubmit = (e: JSX.TargetedEvent<HTMLFormElement, Event>) => {
    e.preventDefault();
    console.log('Form submitted');
  };

  const handleChange = (e: JSX.TargetedEvent<HTMLInputElement, Event>) => {
    console.log('Input value:', e.currentTarget.value);
  };

  const handleClick = (e: JSX.TargetedMouseEvent<HTMLButtonElement>) => {
    console.log('Button clicked at', e.clientX, e.clientY);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input type="text" onChange={handleChange} />
      <button onClick={handleClick}>Submit</button>
    </form>
  );
}

Common event types:

JSX.TargetedEvent<T, E> - Generic event
JSX.TargetedMouseEvent<T> - Mouse events
JSX.TargetedKeyboardEvent<T> - Keyboard events
JSX.TargetedFocusEvent<T> - Focus events

Refs with TypeScript

import { Component } from 'preact';
import { createRef } from 'preact';

class VideoPlayer extends Component {
  play() {
    console.log('Playing...');
  }

  pause() {
    console.log('Paused');
  }
}

class VideoController extends Component {
  playerRef = createRef<VideoPlayer>();

  handlePlay = () => {
    this.playerRef.current?.play();
  };

  handlePause = () => {
    this.playerRef.current?.pause();
  };

  render() {
    return (
      <div>
        <VideoPlayer ref={this.playerRef} />
        <button onClick={this.handlePlay}>Play</button>
        <button onClick={this.handlePause}>Pause</button>
      </div>
    );
  }
}

Context with TypeScript

import { createContext } from 'preact';
import { useContext, useState } from 'preact/hooks';

interface User {
  id: string;
  name: string;
  email: string;
}

interface AuthContextValue {
  user: User | null;
  login: (email: string, password: string) => Promise<void>;
  logout: () => void;
}

const AuthContext = createContext<AuthContextValue | undefined>(undefined);

export function AuthProvider({ children }: { children: ComponentChildren }) {
  const [user, setUser] = useState<User | null>(null);

  const login = async (email: string, password: string) => {
    const response = await fetch('/api/login', {
      method: 'POST',
      body: JSON.stringify({ email, password })
    });
    const userData = await response.json();
    setUser(userData);
  };

  const logout = () => {
    setUser(null);
  };

  return (
    <AuthContext.Provider value={{ user, login, logout }}>
      {children}
    </AuthContext.Provider>
  );
}

export function useAuth() {
  const context = useContext(AuthContext);
  if (!context) {
    throw new Error('useAuth must be used within AuthProvider');
  }
  return context;
}

Custom Hooks

Type your custom hooks like regular functions:

import { useState, useEffect } from 'preact/hooks';

interface FetchState<T> {
  data: T | null;
  loading: boolean;
  error: Error | null;
}

function useFetch<T>(url: string): FetchState<T> {
  const [state, setState] = useState<FetchState<T>>({
    data: null,
    loading: true,
    error: null
  });

  useEffect(() => {
    let cancelled = false;

    fetch(url)
      .then(res => res.json())
      .then(data => {
        if (!cancelled) {
          setState({ data, loading: false, error: null });
        }
      })
      .catch(error => {
        if (!cancelled) {
          setState({ data: null, loading: false, error });
        }
      });

    return () => {
      cancelled = true;
    };
  }, [url]);

  return state;
}

// Usage
interface User {
  id: number;
  name: string;
}

function UserProfile({ userId }: { userId: number }) {
  const { data, loading, error } = useFetch<User>(
    `/api/users/${userId}`
  );

  if (loading) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;
  if (!data) return <div>No data</div>;

  return <div>{data.name}</div>;
}

Generic Components

Create reusable components that work with any type:

import { ComponentChildren } from 'preact';

interface ListProps<T> {
  items: T[];
  renderItem: (item: T) => ComponentChildren;
  keyExtractor: (item: T) => string | number;
}

function List<T>({ items, renderItem, keyExtractor }: ListProps<T>) {
  return (
    <ul>
      {items.map(item => (
        <li key={keyExtractor(item)}>
          {renderItem(item)}
        </li>
      ))}
    </ul>
  );
}

// Usage
interface User {
  id: number;
  name: string;
}

const users: User[] = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' }
];

function App() {
  return (
    <List
      items={users}
      renderItem={user => <span>{user.name}</span>}
      keyExtractor={user => user.id}
    />
  );
}

Utility Types

Preact exports useful utility types:

import {
  ComponentChildren,
  ComponentType,
  VNode,
  RefObject,
  ComponentProps
} from 'preact';

// Get props type from a component
const Button: FunctionComponent<{ label: string }> = ({ label }) => (
  <button>{label}</button>
);

type ButtonProps = ComponentProps<typeof Button>;
// { label: string; children?: ComponentChildren }

// RefObject type
const ref: RefObject<HTMLDivElement> = { current: null };

// VNode type
const vnode: VNode = <div>Hello</div>;

Best Practices

Enable strict mode

{
  "compilerOptions": {
    "strict": true,
    "strictNullChecks": true,
    "noImplicitAny": true
  }
}

Use inference when possible

// Good: Type is inferred
const [count, setCount] = useState(0);

// Unnecessary: Type already inferred
const [count, setCount] = useState<number>(0);

// Necessary: Complex type or null initial value
const [user, setUser] = useState<User | null>(null);

Create interfaces for props

// Good: Reusable interface
interface ButtonProps {
  label: string;
  onClick: () => void;
  variant?: 'primary' | 'secondary';
}

function Button({ label, onClick, variant = 'primary' }: ButtonProps) {
  return (
    <button className={variant} onClick={onClick}>
      {label}
    </button>
  );
}

Use discriminated unions for state

type AsyncState<T> =
  | { status: 'idle' }
  | { status: 'loading' }
  | { status: 'success'; data: T }
  | { status: 'error'; error: Error };

function UserProfile() {
  const [state, setState] = useState<AsyncState<User>>({ 
    status: 'idle' 
  });

  if (state.status === 'loading') return <div>Loading...</div>;
  if (state.status === 'error') return <div>{state.error.message}</div>;
  if (state.status === 'success') return <div>{state.data.name}</div>;
  return null;
}

Getting Started

Core Concepts

Guides

React Compatibility

Advanced

Setup

Type Definitions

Component Types

Props with Children

Hooks with TypeScript

Event Handlers

Refs with TypeScript

Context with TypeScript

Custom Hooks

Generic Components

Utility Types

Best Practices

Next Steps

Hooks

Context

Build docs developers (and LLMs) love

Getting Started

Core Concepts

Guides

React Compatibility

Advanced

​Setup

​Type Definitions

​Component Types

​Props with Children

​Hooks with TypeScript

​Event Handlers

​Refs with TypeScript

​Context with TypeScript

​Custom Hooks

​Generic Components

​Utility Types

​Best Practices

​Next Steps

Hooks

Context

Build docs developers (and LLMs) love

Setup

Type Definitions

Component Types

Props with Children

Hooks with TypeScript

Event Handlers

Refs with TypeScript

Context with TypeScript

Custom Hooks

Generic Components

Utility Types

Best Practices

Next Steps