Preact - 💧 Mizu

Preact is a fast 3kB alternative to React with the same modern API. It delivers the same component-based architecture and hooks as React, but with a significantly smaller footprint and better performance. When you want React’s developer experience without the bundle size overhead, Preact is the perfect choice.

Why Preact?

Preact brings all the power of modern React development with exceptional performance: Tiny Bundle Size - Only 3kB gzipped vs React’s ~45kB. Perfect for mobile-first applications. Blazing Fast - Smaller runtime means faster parsing, faster execution, and better performance on low-end devices. React Compatible - Use preact/compat to run most React libraries unchanged. Same hooks API, same patterns. Modern Features - Hooks, fragments, context, concurrent rendering, and more. Signals - Unique fine-grained reactivity system that’s even faster than hooks. No Build Required - Can run directly in browsers with ES modules (though bundling is recommended).

Preact vs React Comparison

Feature	Preact	React
Bundle Size	3kB	~45kB
Runtime Speed	⚡ Faster	⚡ Fast
API Compatibility	~95% with compat	100%
Hooks	✅ Yes	✅ Yes
Fragments	✅ Yes	✅ Yes
Context	✅ Yes	✅ Yes
Signals	✅ Unique feature	❌ No
DevTools	✅ Yes	✅ Yes
Ecosystem	⚠️ Smaller	✅ Huge
Learning Curve	✅ Easy (if you know React)	⚠️ Moderate
TypeScript	✅ Full support	✅ Full support
Best for	Performance-critical apps	Large ecosystems

Bundle Size Comparison

Real-world bundle sizes (production, gzipped):

Hello World App:
├── Preact:        ~4 KB   (library + app code)
├── React:         ~42 KB  (library + app code)
└── Savings:       ~38 KB  (90% smaller!)

Todo App:
├── Preact:        ~8 KB
├── React:         ~46 KB
└── Savings:       ~38 KB  (82% smaller!)

Full App (with routing):
├── Preact:        ~15 KB
├── React:         ~52 KB
└── Savings:       ~37 KB  (71% smaller!)

This means:

Faster initial load (especially on slow connections)
Better performance on mobile devices
Lower bandwidth costs
Improved Core Web Vitals scores

Quick Start

Create a new Preact project with the CLI:

mizu new ./my-preact-app --template frontend/preact
cd my-preact-app
make dev

Visit http://localhost:3000 to see your app!

Project Structure

my-preact-app/
├── cmd/
│   └── server/
│       └── main.go              # Go entry point
├── app/
│   └── server/
│       ├── app.go               # Mizu app configuration
│       ├── config.go            # Server configuration
│       └── routes.go            # API routes (Go)
├── frontend/                      # Preact application
│   ├── src/
│   │   ├── main.jsx            # App entry point
│   │   ├── app.jsx             # Root component
│   │   ├── components/
│   │   │   ├── Header.jsx
│   │   │   ├── Footer.jsx
│   │   │   └── UserCard.jsx
│   │   ├── pages/
│   │   │   ├── Home.jsx
│   │   │   ├── About.jsx
│   │   │   └── Users.jsx
│   │   ├── hooks/
│   │   │   ├── useUsers.js
│   │   │   └── useAuth.js
│   │   ├── store/              # Signals store
│   │   │   └── users.js
│   │   └── styles/
│   │       └── index.css
│   ├── public/
│   │   └── favicon.ico
│   ├── index.html
│   ├── package.json
│   ├── vite.config.js
│   └── tsconfig.json
├── dist/                        # Built files
└── Makefile

Configuration

Vite Configuration

Configure Vite for Preact with React compatibility:

`frontend/vite.config.js`

import { defineConfig } from 'vite'
import preact from '@preact/preset-vite'

export default defineConfig({
  plugins: [preact()],

  // React compatibility (optional)
  resolve: {
    alias: {
      'react': 'preact/compat',
      'react-dom': 'preact/compat',
      'react/jsx-runtime': 'preact/jsx-runtime'
    }
  },

  server: {
    port: 5173,
    strictPort: true,
    hmr: {
      clientPort: 3000  // Mizu's port for HMR
    }
  },

  build: {
    outDir: '../dist',
    emptyOutDir: true,

    // Optimize for size
    rollupOptions: {
      output: {
        manualChunks: undefined  // Keep bundle small
      }
    },

    // Smaller chunk size limit
    chunkSizeWarningLimit: 100
  }
})

Why use aliases?

Use existing React libraries without modification
Gradual migration from React to Preact
Access to React ecosystem (react-router, etc.)

Backend Configuration

`app/server/app.go`

package server

import (
    "embed"
    "io/fs"

    "github.com/go-mizu/mizu"
    "github.com/go-mizu/mizu/frontend"
)

//go:embed all:../../dist
var distFS embed.FS

func New(cfg *Config) *mizu.App {
    app := mizu.New()

    // API routes
    setupRoutes(app)

    // Frontend middleware
    dist, _ := fs.Sub(distFS, "dist")
    app.Use(frontend.WithOptions(frontend.Options{
        Mode:        frontend.ModeAuto,
        FS:          dist,
        Root:        "./dist",
        DevServer:   "http://localhost:" + cfg.DevPort,
        IgnorePaths: []string{"/api"},
    }))

    return app
}

Preact vs React: Key Differences

While Preact is largely compatible with React, there are some differences:

1. Import Paths

// React
import React from 'react'
import { useState, useEffect } from 'react'
import ReactDOM from 'react-dom'

// Preact (native)
import { h, render } from 'preact'
import { useState, useEffect } from 'preact/hooks'

// Preact (with compat - React-style imports)
import React, { useState, useEffect } from 'react'
import ReactDOM from 'react-dom'

2. JSX Pragma

Preact uses h function instead of React.createElement:

// React (implicit)
<div>Hello</div>
// Compiles to: React.createElement('div', null, 'Hello')

// Preact (implicit with preset)
<div>Hello</div>
// Compiles to: h('div', null, 'Hello')

// Preact (explicit pragma - not needed with preset)
/** @jsx h */
import { h } from 'preact'

With @preact/preset-vite, you don’t need to import h manually.

3. Event Naming

Preact uses standard DOM event names:

// React (camelCase)
<button onClick={handleClick}>Click</button>
<input onChange={handleChange} />

// Preact (lowercase also works, but camelCase preferred)
<button onClick={handleClick}>Click</button>
<input onInput={handleInput} />  // Note: onInput instead of onChange

Important: Preact uses onInput for real-time updates, while React uses onChange.

4. Class Names

Both support className, but Preact also supports class:

// React (only className)
<div className="container">Content</div>

// Preact (both work)
<div className="container">Content</div>
<div class="container">Content</div>

5. defaultValue vs value

// React (controlled by default)
<input value={value} onChange={onChange} />

// Preact (more flexible)
<input value={value} onInput={onInput} />
<input defaultValue={value} />  // Uncontrolled

Components

Function Components

// Basic component
function Welcome({ name }) {
  return <h1>Hello, {name}!</h1>
}

// With destructuring and default props
function Card({ title, content = 'No content' }) {
  return (
    <div class="card">
      <h2>{title}</h2>
      <p>{content}</p>
    </div>
  )
}

// With TypeScript
interface UserProps {
  user: {
    id: number
    name: string
    email: string
  }
}

function UserProfile({ user }: UserProps) {
  return (
    <div>
      <h1>{user.name}</h1>
      <p>{user.email}</p>
    </div>
  )
}

Class Components

While hooks are preferred, class components work too:

import { Component } from 'preact'

class Counter extends Component {
  state = { count: 0 }

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

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

Hooks

Preact supports all React hooks:

useState

import { useState } from 'preact/hooks'

function Counter() {
  const [count, setCount] = useState(0)
  const [name, setName] = useState('Guest')

  return (
    <div>
      <p>{name}: {count}</p>
      <button onClick={() => setCount(count + 1)}>+</button>
      <input
        value={name}
        onInput={(e) => setName(e.target.value)}
      />
    </div>
  )
}

useEffect

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

function Users() {
  const [users, setUsers] = useState([])
  const [loading, setLoading] = useState(true)

  useEffect(() => {
    fetch('/api/users')
      .then(res => res.json())
      .then(data => {
        setUsers(data)
        setLoading(false)
      })
  }, [])  // Empty deps = run once on mount

  if (loading) return <div>Loading...</div>

  return (
    <ul>
      {users.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  )
}

useReducer

import { useReducer } from 'preact/hooks'

const initialState = { count: 0 }

function reducer(state, action) {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 }
    case 'decrement':
      return { count: state.count - 1 }
    case 'reset':
      return initialState
    default:
      return state
  }
}

function Counter() {
  const [state, dispatch] = useReducer(reducer, initialState)

  return (
    <div>
      <p>Count: {state.count}</p>
      <button onClick={() => dispatch({ type: 'increment' })}>+</button>
      <button onClick={() => dispatch({ type: 'decrement' })}>-</button>
      <button onClick={() => dispatch({ type: 'reset' })}>Reset</button>
    </div>
  )
}

useContext

import { createContext } from 'preact'
import { useContext } from 'preact/hooks'

const ThemeContext = createContext('light')

function App() {
  return (
    <ThemeContext.Provider value="dark">
      <ThemedButton />
    </ThemeContext.Provider>
  )
}

function ThemedButton() {
  const theme = useContext(ThemeContext)

  return (
    <button class={`btn-${theme}`}>
      Themed Button
    </button>
  )
}

useMemo and useCallback

import { useMemo, useCallback, useState } from 'preact/hooks'

function ExpensiveComponent({ items }) {
  const [filter, setFilter] = useState('')

  // Memoize expensive calculation
  const filteredItems = useMemo(() => {
    console.log('Filtering items...')
    return items.filter(item =>
      item.name.toLowerCase().includes(filter.toLowerCase())
    )
  }, [items, filter])

  // Memoize callback
  const handleFilter = useCallback((e) => {
    setFilter(e.target.value)
  }, [])

  return (
    <div>
      <input value={filter} onInput={handleFilter} />
      <ul>
        {filteredItems.map(item => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
    </div>
  )
}

useRef

import { useRef, useEffect } from 'preact/hooks'

function AutoFocusInput() {
  const inputRef = useRef(null)

  useEffect(() => {
    // Focus input on mount
    inputRef.current?.focus()
  }, [])

  return <input ref={inputRef} placeholder="Auto-focused" />
}

Custom Hooks

// hooks/useUsers.js
import { useState, useEffect } from 'preact/hooks'

export function useUsers() {
  const [users, setUsers] = useState([])
  const [loading, setLoading] = useState(true)
  const [error, setError] = useState(null)

  useEffect(() => {
    fetch('/api/users')
      .then(res => {
        if (!res.ok) throw new Error('Failed to fetch')
        return res.json()
      })
      .then(setUsers)
      .catch(setError)
      .finally(() => setLoading(false))
  }, [])

  const addUser = async (user) => {
    const res = await fetch('/api/users', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(user)
    })
    const newUser = await res.json()
    setUsers([...users, newUser])
  }

  const deleteUser = async (id) => {
    await fetch(`/api/users/${id}`, { method: 'DELETE' })
    setUsers(users.filter(u => u.id !== id))
  }

  return { users, loading, error, addUser, deleteUser }
}

Usage:

import { useUsers } from './hooks/useUsers'

function UserList() {
  const { users, loading, error, deleteUser } = useUsers()

  if (loading) return <div>Loading...</div>
  if (error) return <div>Error: {error.message}</div>

  return (
    <ul>
      {users.map(user => (
        <li key={user.id}>
          {user.name}
          <button onClick={() => deleteUser(user.id)}>Delete</button>
        </li>
      ))}
    </ul>
  )
}

Preact Signals

Signals are Preact’s unique fine-grained reactivity system. They’re faster and simpler than hooks for state management.

What are Signals?

Signals are reactive primitives that automatically update components when their value changes:

import { signal } from '@preact/signals'

// Create a signal
const count = signal(0)

// Read value
console.log(count.value)  // 0

// Update value
count.value++  // Components using count will auto-update!

Why Signals?

Performance:

No re-renders! Components only update the specific DOM nodes that changed
Skip Virtual DOM diffing
Faster than useState for frequently updating state

Simplicity:

No dependency arrays
No useMemo/useCallback needed
Share state without Context API

Size:

Signals add only ~1.6kB to your bundle

Basic Signals

import { signal } from '@preact/signals'

// Global signal (outside component)
const count = signal(0)

function Counter() {
  // Signal value is accessed with .value
  // But in JSX, you can use the signal directly!
  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => count.value++}>+</button>
      <button onClick={() => count.value--}>-</button>
    </div>
  )
}

Key points:

Access/update with .value in JavaScript
Use signal directly in JSX (no .value needed)
Changes trigger automatic, fine-grained updates

Computed Signals

Derived values that automatically update:

import { signal, computed } from '@preact/signals'

const count = signal(0)
const doubled = computed(() => count.value * 2)

function App() {
  return (
    <div>
      <p>Count: {count}</p>
      <p>Doubled: {doubled}</p>
      <button onClick={() => count.value++}>Increment</button>
    </div>
  )
}

Computed signals:

Only recalculate when dependencies change
Cached automatically
Can depend on other computed signals

Effect Signal

Run side effects when signals change:

import { signal, effect } from '@preact/signals'

const count = signal(0)

effect(() => {
  console.log('Count changed to:', count.value)
})

// Now whenever count changes, the effect runs
count.value = 5  // Logs: "Count changed to: 5"

Signals for State Management

Create a global store with signals:

// store/users.js
import { signal, computed } from '@preact/signals'

export const users = signal([])
export const filter = signal('')

export const filteredUsers = computed(() => {
  const f = filter.value.toLowerCase()
  return users.value.filter(u =>
    u.name.toLowerCase().includes(f)
  )
})

export const userCount = computed(() => users.value.length)

export async function fetchUsers() {
  const res = await fetch('/api/users')
  users.value = await res.json()
}

export function addUser(user) {
  users.value = [...users.value, user]
}

export function deleteUser(id) {
  users.value = users.value.filter(u => u.id !== id)
}

Use in components:

import { users, filteredUsers, filter, fetchUsers, deleteUser } from './store/users'
import { useEffect } from 'preact/hooks'

function UserList() {
  useEffect(() => {
    fetchUsers()
  }, [])

  return (
    <div>
      <input
        value={filter}
        onInput={(e) => filter.value = e.target.value}
        placeholder="Filter users..."
      />

      <p>Total: {users.value.length}</p>

      <ul>
        {filteredUsers.value.map(user => (
          <li key={user.id}>
            {user.name}
            <button onClick={() => deleteUser(user.id)}>×</button>
          </li>
        ))}
      </ul>
    </div>
  )
}

Signals vs Hooks

Feature	Signals	Hooks (useState)
Bundle Size	+1.6kB	Included
Performance	⚡ Fastest	⚡ Fast
Re-renders	❌ No	✅ Yes
Global State	✅ Easy	⚠️ Needs Context
Computed Values	✅ Built-in	⚠️ useMemo
Learning Curve	✅ Simple	✅ Familiar
Best for	Shared state, counters, filters	Local component state

Rule of thumb:

Use Signals for: Global state, frequently updated values, shared state
Use Hooks for: Local component state, one-time effects, familiar patterns

Routing

Preact doesn’t include routing, but you have options:

Option 1: preact-router (Recommended)

Lightweight routing made for Preact:

npm install preact-router

import { Router, Route } from 'preact-router'
import Home from './pages/Home'
import About from './pages/About'
import Users from './pages/Users'
import User from './pages/User'

function App() {
  return (
    <div>
      <nav>
        <a href="/">Home</a>
        <a href="/about">About</a>
        <a href="/users">Users</a>
      </nav>

      <Router>
        <Route path="/" component={Home} />
        <Route path="/about" component={About} />
        <Route path="/users" component={Users} />
        <Route path="/users/:id" component={User} />
      </Router>
    </div>
  )
}

Access route params:

function User({ id }) {
  return <h1>User {id}</h1>
}

Programmatic navigation:

import { route } from 'preact-router'

function handleClick() {
  route('/users')
}

Option 2: React Router (with compat)

Use React Router with preact/compat:

npm install react-router-dom

import { BrowserRouter, Routes, Route, Link } from 'react-router-dom'
import Home from './pages/Home'
import About from './pages/About'

function App() {
  return (
    <BrowserRouter>
      <nav>
        <Link to="/">Home</Link>
        <Link to="/about">About</Link>
      </nav>

      <Routes>
        <Route path="/" element={<Home />} />
        <Route path="/about" element={<About />} />
      </Routes>
    </BrowserRouter>
  )
}

Option 3: wouter (Minimalist)

Tiny routing library:

npm install wouter wouter-preact

import { Route, Link } from 'wouter-preact'

function App() {
  return (
    <div>
      <Link href="/">Home</Link>
      <Link href="/about">About</Link>

      <Route path="/" component={Home} />
      <Route path="/about" component={About} />
    </div>
  )
}

React Compatibility (preact/compat)

Run most React libraries unchanged with preact/compat.

Setup

Already configured in the Vite config above. Just install React libraries:

npm install react-router-dom
npm install react-query
npm install react-hook-form

Import as normal:

import { useForm } from 'react-hook-form'
import { useQuery } from 'react-query'

function MyForm() {
  const { register, handleSubmit } = useForm()

  const { data } = useQuery('users', () =>
    fetch('/api/users').then(r => r.json())
  )

  return <form onSubmit={handleSubmit}>...</form>
}

What Works

Most React libraries work out of the box: ✅ Routing: react-router-dom, wouter ✅ Forms: react-hook-form, formik ✅ State: zustand, jotai ✅ Data Fetching: react-query, swr ✅ UI Libraries: Many work (test first) ✅ Styling: styled-components, emotion

What Doesn’t Work

❌ React-specific internals: Libraries using React internals ❌ React Native: Web only ❌ Some UI libraries: Material-UI, Chakra (use Preact alternatives)

Testing Compatibility

To test if a library works:

import { useState } from 'react'  // Uses preact/compat
import SomeLibrary from 'some-library'

function Test() {
  return <SomeLibrary />
}

If it renders without errors, it works!

Styling

CSS Modules

import styles from './Button.module.css'

function Button({ children }) {
  return (
    <button class={styles.button}>
      {children}
    </button>
  )
}

/* Button.module.css */
.button {
  background: #007bff;
  color: white;
  padding: 0.5rem 1rem;
  border: none;
  border-radius: 4px;
}

Tailwind CSS

Install Tailwind:

npm install -D tailwindcss postcss autoprefixer
npx tailwindcss init -p

Configure tailwind.config.js:

export default {
  content: [
    "./index.html",
    "./src/**/*.{js,jsx,ts,tsx}",
  ],
  theme: {
    extend: {},
  },
  plugins: [],
}

Use in components:

function Button() {
  return (
    <button class="bg-blue-500 text-white px-4 py-2 rounded hover:bg-blue-600">
      Click me
    </button>
  )
}

Styled Components

npm install styled-components

import styled from 'styled-components'

const Button = styled.button`
  background: #007bff;
  color: white;
  padding: 0.5rem 1rem;
  border: none;
  border-radius: 4px;

  &:hover {
    background: #0056b3;
  }
`

function App() {
  return <Button>Click me</Button>
}

Development Workflow

Starting Development

# Option 1: Makefile (recommended)
make dev

# Option 2: Manual (two terminals)
# Terminal 1: Preact dev server
cd frontend
npm run dev

# Terminal 2: Mizu server
go run cmd/server/main.go

Visit http://localhost:3000

Hot Module Replacement

Preact supports Fast Refresh:

Edit components → instant updates
State preserved during updates
No full page reload

DevTools

Install Preact DevTools extension:

Features:

Inspect component tree
View props and state
Track re-renders
Performance profiling

Building for Production

make build

This:

Builds Preact app (npm run build)
Builds Go binary with embedded frontend

Build Optimizations

The Preact template includes optimizations: Code splitting:

// Lazy load routes
import { lazy } from 'preact/compat'

const About = lazy(() => import('./pages/About'))

<Route path="/about" component={About} />

Tree shaking:

// Import only what you need
import { signal } from '@preact/signals'  // ✅
import * as signals from '@preact/signals'  // ❌

Bundle analysis:

npm run build -- --mode analyze

Production Checklist

TypeScript

Preact has excellent TypeScript support:

// Component with props
interface ButtonProps {
  onClick: () => void
  children: preact.ComponentChildren
  variant?: 'primary' | 'secondary'
}

function Button({ onClick, children, variant = 'primary' }: ButtonProps) {
  return (
    <button class={`btn-${variant}`} onClick={onClick}>
      {children}
    </button>
  )
}

// With generic types
interface ListProps<T> {
  items: T[]
  renderItem: (item: T) => preact.VNode
}

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

Typed Hooks

import { useState } from 'preact/hooks'

// Type inference
const [count, setCount] = useState(0)  // number

// Explicit types
const [user, setUser] = useState<User | null>(null)

// Typed ref
const inputRef = useRef<HTMLInputElement>(null)

Typed Signals

import { signal, Signal } from '@preact/signals'

// Type inference
const count = signal(0)  // Signal<number>

// Explicit type
const user: Signal<User | null> = signal(null)

Real-World Example: Todo App with Signals

Complete todo app using Signals:

Backend

// app/server/routes.go
type Todo struct {
    ID        int    `json:"id"`
    Title     string `json:"title"`
    Completed bool   `json:"completed"`
}

var todos = []Todo{
    {ID: 1, Title: "Learn Preact", Completed: true},
    {ID: 2, Title: "Build app", Completed: false},
}

func setupRoutes(app *mizu.App) {
    app.Get("/api/todos", handleTodos)
    app.Post("/api/todos", createTodo)
    app.Put("/api/todos/{id}", updateTodo)
    app.Delete("/api/todos/{id}", deleteTodo)
}

func handleTodos(c *mizu.Ctx) error {
    return c.JSON(200, todos)
}

Store with Signals

// store/todos.js
import { signal, computed } from '@preact/signals'

export const todos = signal([])
export const filter = signal('all')  // 'all' | 'active' | 'completed'
export const newTodoText = signal('')

export const filteredTodos = computed(() => {
  switch (filter.value) {
    case 'active':
      return todos.value.filter(t => !t.completed)
    case 'completed':
      return todos.value.filter(t => t.completed)
    default:
      return todos.value
  }
})

export const activeCount = computed(() =>
  todos.value.filter(t => !t.completed).length
)

export async function fetchTodos() {
  const res = await fetch('/api/todos')
  todos.value = await res.json()
}

export async function addTodo() {
  if (!newTodoText.value.trim()) return

  const res = await fetch('/api/todos', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ title: newTodoText.value, completed: false })
  })

  const todo = await res.json()
  todos.value = [...todos.value, todo]
  newTodoText.value = ''
}

export async function toggleTodo(id) {
  const todo = todos.value.find(t => t.id === id)
  if (!todo) return

  await fetch(`/api/todos/${id}`, {
    method: 'PUT',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ ...todo, completed: !todo.completed })
  })

  todos.value = todos.value.map(t =>
    t.id === id ? { ...t, completed: !t.completed } : t
  )
}

export async function deleteTodo(id) {
  await fetch(`/api/todos/${id}`, { method: 'DELETE' })
  todos.value = todos.value.filter(t => t.id !== id)
}

Components

// App.jsx
import { useEffect } from 'preact/hooks'
import { fetchTodos } from './store/todos'
import TodoForm from './components/TodoForm'
import TodoFilters from './components/TodoFilters'
import TodoList from './components/TodoList'
import './App.css'

export function App() {
  useEffect(() => {
    fetchTodos()
  }, [])

  return (
    <div class="app">
      <h1>Todos</h1>
      <TodoForm />
      <TodoFilters />
      <TodoList />
    </div>
  )
}

// components/TodoForm.jsx
import { newTodoText, addTodo } from '../store/todos'

export default function TodoForm() {
  const handleSubmit = (e) => {
    e.preventDefault()
    addTodo()
  }

  return (
    <form onSubmit={handleSubmit} class="todo-form">
      <input
        value={newTodoText}
        onInput={(e) => newTodoText.value = e.target.value}
        placeholder="What needs to be done?"
        class="todo-input"
      />
      <button type="submit">Add</button>
    </form>
  )
}

// components/TodoFilters.jsx
import { filter, activeCount } from '../store/todos'

export default function TodoFilters() {
  return (
    <div class="filters">
      <button
        class={filter.value === 'all' ? 'active' : ''}
        onClick={() => filter.value = 'all'}
      >
        All
      </button>
      <button
        class={filter.value === 'active' ? 'active' : ''}
        onClick={() => filter.value = 'active'}
      >
        Active ({activeCount})
      </button>
      <button
        class={filter.value === 'completed' ? 'active' : ''}
        onClick={() => filter.value = 'completed'}
      >
        Completed
      </button>
    </div>
  )
}

// components/TodoList.jsx
import { filteredTodos, toggleTodo, deleteTodo } from '../store/todos'

export default function TodoList() {
  if (filteredTodos.value.length === 0) {
    return <p class="empty">No todos found</p>
  }

  return (
    <ul class="todo-list">
      {filteredTodos.value.map(todo => (
        <li key={todo.id} class={todo.completed ? 'completed' : ''}>
          <input
            type="checkbox"
            checked={todo.completed}
            onChange={() => toggleTodo(todo.id)}
          />
          <span>{todo.title}</span>
          <button onClick={() => deleteTodo(todo.id)}>×</button>
        </li>
      ))}
    </ul>
  )
}

Migration from React

Step 1: Install Preact

npm install preact
npm install -D @preact/preset-vite

Step 2: Update Vite Config

import { defineConfig } from 'vite'
import preact from '@preact/preset-vite'

export default defineConfig({
  plugins: [preact()],
  resolve: {
    alias: {
      'react': 'preact/compat',
      'react-dom': 'preact/compat',
      'react/jsx-runtime': 'preact/jsx-runtime'
    }
  }
})

Step 3: Update Imports (Gradual)

// Before (React)
import React, { useState } from 'react'
import ReactDOM from 'react-dom'

// After (keep same - compat aliased)
import React, { useState } from 'react'
import ReactDOM from 'react-dom'

// Or switch to Preact native (optional, over time)
import { useState } from 'preact/hooks'
import { render } from 'preact'

Step 4: Test

Run your app. Most things should work immediately!

Step 5: Optimize (Optional)

Replace compat imports with Preact native:

// From
import { useState } from 'react'

// To
import { useState } from 'preact/hooks'

Replace React Router with preact-router:

// From
import { BrowserRouter, Route } from 'react-router-dom'

// To
import { Router, Route } from 'preact-router'

Consider using Signals for state management.

Performance Tips

1. Use Signals for Shared State

// ❌ Slower: Context + useState
const [users, setUsers] = useState([])

// ✅ Faster: Signals
const users = signal([])

2. Lazy Load Routes

import { lazy } from 'preact/compat'

const About = lazy(() => import('./pages/About'))

3. Avoid Inline Functions

// ❌ Creates new function on every render
<button onClick={() => handleClick(id)}>Click</button>

// ✅ Reuse function
const onClick = () => handleClick(id)
<button onClick={onClick}>Click</button>

4. Use Keys in Lists

// ✅ Proper keys
{items.map(item => <li key={item.id}>{item.name}</li>)}

// ❌ Index as key (avoid if list changes)
{items.map((item, i) => <li key={i}>{item.name}</li>)}

5. Measure Bundle Size

npm run build
ls -lh dist/assets/*.js

Aim for:

Total JS: <20kB (with routing)
Main bundle: <15kB

Troubleshooting

`h` is not defined

Error:

ReferenceError: h is not defined

Cause: Not using @preact/preset-vite Solution: Install preset:

npm install -D @preact/preset-vite

Update vite.config.js:

import preact from '@preact/preset-vite'

export default {
  plugins: [preact()]
}

React Library Doesn’t Work

Symptom: React library throws errors Solution: Check if compat is configured:

// vite.config.js
export default {
  resolve: {
    alias: {
      'react': 'preact/compat',
      'react-dom': 'preact/compat'
    }
  }
}

If still broken, the library may use React internals. Find a Preact alternative.

onChange Not Firing

Cause: Preact uses onInput for real-time updates Solution:

// React
<input onChange={handleChange} />

// Preact
<input onInput={handleChange} />

DevTools Not Working

Solution: Install Preact DevTools (not React DevTools):

Bundle Size Too Large

Check:

npm run build
ls -lh dist/assets/

Solutions:

Remove unused dependencies
Use dynamic imports for routes
Check for duplicate React/Preact
Use Signals instead of heavy state libraries

When to Choose Preact

Choose Preact When:

✅ Bundle size is critical (mobile, emerging markets) ✅ You want React DX with better performance ✅ Building performance-critical applications ✅ You need fine-grained reactivity (Signals) ✅ Migrating from React but want smaller bundle ✅ Every kilobyte counts ✅ You value simplicity and speed

Choose React When:

✅ You need the full React ecosystem ✅ Using React-specific libraries ✅ Team is deeply invested in React ✅ Bundle size doesn’t matter ✅ Need bleeding-edge React features first

Choose Something Else When:

Need SSR/SSG: Use Next.js, Nuxt, or SvelteKit
Want full framework: Use Nuxt, Next.js, or Angular
Hate JSX: Use Vue or Svelte
Want even smaller: Use vanilla JS or Alpine.js

Next Steps

React Guide

Compare with full React setup

Signals Documentation

Deep dive into Signals

Preact Router

Routing documentation

preact/compat

React compatibility guide

​Why Preact?

​Preact vs React Comparison

​Bundle Size Comparison

​Quick Start

​Project Structure

​Configuration

​Vite Configuration

​frontend/vite.config.js

​Backend Configuration

​app/server/app.go

​Preact vs React: Key Differences

​1. Import Paths

​2. JSX Pragma

​3. Event Naming

​4. Class Names

​5. defaultValue vs value

​Components

​Function Components

​Class Components

​Hooks

​useState

​useEffect

​useReducer

​useContext

​useMemo and useCallback

​useRef

​Custom Hooks

​Preact Signals

​What are Signals?

​Why Signals?

​Basic Signals

​Computed Signals

​Effect Signal

​Signals for State Management

​Signals vs Hooks

​Routing

​Option 1: preact-router (Recommended)

​Option 2: React Router (with compat)

​Option 3: wouter (Minimalist)

​React Compatibility (preact/compat)

​Setup

​What Works

​What Doesn’t Work

​Testing Compatibility

​Styling

​CSS Modules

​Tailwind CSS

​Styled Components

​Development Workflow

​Starting Development

​Hot Module Replacement

​DevTools

​Building for Production

​Build Optimizations

​Production Checklist

​TypeScript

​Typed Hooks

​Typed Signals

​Real-World Example: Todo App with Signals

​Backend

​Store with Signals

​Components

​Migration from React

​Step 1: Install Preact

​Step 2: Update Vite Config

​Step 3: Update Imports (Gradual)

​Step 4: Test

​Step 5: Optimize (Optional)

​Performance Tips

​1. Use Signals for Shared State

​2. Lazy Load Routes

​3. Avoid Inline Functions

​4. Use Keys in Lists

​5. Measure Bundle Size

​Troubleshooting

​h is not defined

​React Library Doesn’t Work

​onChange Not Firing

​DevTools Not Working

​Bundle Size Too Large

Why Preact?

Preact vs React Comparison

Bundle Size Comparison

Quick Start

Project Structure

Configuration

Vite Configuration

`frontend/vite.config.js`

Backend Configuration

`app/server/app.go`

Preact vs React: Key Differences

1. Import Paths

2. JSX Pragma

3. Event Naming

4. Class Names

5. defaultValue vs value

Components

Function Components

Class Components

Hooks

useState

useEffect

useReducer

useContext

useMemo and useCallback

useRef

Custom Hooks

Preact Signals

What are Signals?

Why Signals?

Basic Signals

Computed Signals

Effect Signal

Signals for State Management

Signals vs Hooks

Routing

Option 1: preact-router (Recommended)

Option 2: React Router (with compat)

Option 3: wouter (Minimalist)

React Compatibility (preact/compat)

Setup

What Works

What Doesn’t Work

Testing Compatibility

Styling

CSS Modules

Tailwind CSS

Styled Components

Development Workflow

Starting Development

Hot Module Replacement

DevTools

Building for Production

Build Optimizations

Production Checklist

TypeScript

Typed Hooks

Typed Signals

Real-World Example: Todo App with Signals

Backend

Store with Signals

Components

Migration from React

Step 1: Install Preact

Step 2: Update Vite Config

Step 3: Update Imports (Gradual)

Step 4: Test

Step 5: Optimize (Optional)

Performance Tips

1. Use Signals for Shared State

2. Lazy Load Routes

3. Avoid Inline Functions

4. Use Keys in Lists

5. Measure Bundle Size

Troubleshooting

`h` is not defined

React Library Doesn’t Work

onChange Not Firing

DevTools Not Working

Bundle Size Too Large