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πŸ‘» Tiny Concurrent UI library with Fiber.

Build Status Code Coverage npm-v npm-d brotli

  • Concurrent with Fiber β€” This is an amazing idea, which implements the coroutine scheduler in JavaScript, and the rendering is asynchronous, which supports Time slicing and suspense components.

  • Highly-optimized algorithm β€” Fre has a better reconciliation algorithm, which traverses from both ends with O (n) complexity, and supports keyed.

  • Do more with less β€” After tree shaking, project of hello world is only 2KB, but it has most features, virtual DOM, hooks API, Fragment and more.


yarn add fre
import { render, useState } from 'fre'

function App() {
  const [count, setCount] = useState(0)
  return <>
      <button onClick={() => setCount(count + 1)}>+</button>

render(<App />, document.body)

Hooks API


useState is a base API, It will receive initial state and return an Array

You can use it many times, new state is available when component is rerender

function App() {
  const [up, setUp] = useState(0)
  const [down, setDown] = useState(0)
  return (
      <button onClick={() => setUp(up + 1)}>+</button>
      <button onClick={() => setDown(down - 1)}>-</button>


useReducer and useState are almost the same,but useReducer needs a global reducer

function reducer(state, action) {
  switch (action.type) {
    case 'up':
      return { count: state.count + 1 }
    case 'down':
      return { count: state.count - 1 }

function App() {
  const [state, dispatch] = useReducer(reducer, { count: 1 })
  return (
      <button onClick={() => dispatch({ type: 'up' })}>+</button>
      <button onClick={() => dispatch({ type: 'down' })}>-</button>


It is the execution and cleanup of effects, which is represented by the second parameter

useEffect(f)       //  effect (and clean-up) every time
useEffect(f, [])   //  effect (and clean-up) only once in a component's life
useEffect(f, [x])  //  effect (and clean-up) when property x changes in a component's life
function App({ flag }) {
  const [count, setCount] = useState(0)
  useEffect(() => {
    document.title = 'count is ' + count
  }, [flag])
  return (
      <button onClick={() => setCount(count + 1)}>+</button>

If it returns a function, the function can do cleanups:

useEffect(() => {
  document.title = 'count is ' + count
  return () => {
}, [])


More like useEffect, but useLayout is sync and blocking UI.

useLayout(() => {
  document.title = 'count is ' + count
}, [flag])


useMemo has the same rules as useEffect, but useMemo will return a cached value.

const memo = (c) => (props) => useMemo(() => c, [Object.values(props)])


useCallback is based useMemo, it will return a cached function.

const cb = useCallback(() => {
  console.log('cb was cached')
}, [])


useRef will return a function or an object.

function App() {
  useEffect(() => {
    console.log(t) // { current:<div>t</div> }
  const t = useRef(null)
  return <div ref={t}>t</div>

If it uses a function, it can return a cleanup and executes when removed.

function App() {
  const t = useRef((dom) => {
    if (dom) {
    } else {
  return flag && <span ref={t}>I will removed</span>


plugins: [
      runtime: 'automatic',
      importSource: 'fre',

Compare with other frameworks

The comparison is difficult because the roadmap and trade-offs of each framework are different, but we have to do so.

  • react

React is the source of inspiration for fre. Their implementation and asynchronous rendering are similar. The most amazing thing is concurrent mode, which means that react and fre have the same roadmap -- Exploring concurrent use cases.

But at the same time, fre has obvious advantages in reconciliation algorithm and bundle size.

  • vue / preact

To some extent, vue and preact are similar. They have similar synchronous rendering, only the API is different.

The reconciliation algorithm of fre is similar to vue, but the biggest difference is that vue/preact do not support concurrent mode, this means that the roadmap is totally different.

framework concurrent reconcilation algorithm bundle size
fre2 √ β˜…β˜…β˜…β˜… 2kb
react17 √ β˜…β˜… 39kb
vue3 Γ— β˜…β˜…β˜…β˜…β˜… 30kb
preactX Γ— β˜…β˜…β˜…β˜… 4kb


MIT @yisar

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