Start using time slicing through fre.js
Tags: react, vue, preact, fre
Published: 2021-01-09 11:43:26

Do you know time slicing? 

This is an amazing thing in react concurrent mode, which shows that the browser will not be blocked by component rendering.

```js
import { h, render, useState, useEffect } from 'fre'

const UPDATE_EVERY = 500
const BLOCK_FOR = 5
const NUM_COMPONENTS = 100

const App = () => {
  const [count, setCount] = useState(0)

  useEffect(() => {
    setTimeout(() => setCount(count + 1), UPDATE_EVERY)
  })

  const values = []

  for (let i = count; i < count + NUM_COMPONENTS; i++) {
    values.push(i)
  }

  return (
    <div className="wraper">
      <h1>Count: {count}</h1>
      {values.map((value, index) => (
        <SlowComponent key={value} value={value} />
      ))}
    </div>
  )
}

const SlowComponent = ({ value }) => {
  const start = performance.now()
  while (performance.now() - start < BLOCK_FOR) {}

  return <li className="slow">{value}</li>
}

const root = document.getElementById('root')
let div = document.createElement('div')
div.innerHTML = `<style>
body {
  background: #010911;
  font-family: sans-serif;
}
h1 {
  color: rgb(0, 204, 10);
}
#animation {
  width: 380px;
  height: 380px;
  transform: translate(50%, 50%);
  margin: 20px auto;
}
.slow {
  background: #f60066;
  color: white;
  padding: 5px;
  display: inline-block;
  margin: 5px;
  font-size: 12px;
  border-radius: 50%;
}
.wraper{
  margin: 20px auto;
  width: 700px;
  text-align: center;
}
ul.solarsystem {
  position: relative;
  height: 400px;
  list-style: none;
  transition: all 0.09s ease-in;
  transform: translate(-480px, -336px);
}
ul.solarsystem li {
  text-indent: -9999px;
  display: block;
  position: absolute;
  border: 2px solid #394057;
}
ul.solarsystem li span {
  display: block;
  position: absolute;
  width: 10px;
  height: 10px;
  border-radius: 5px;
}
ul.solarsystem li.active.sun span,
ul.solarsystem li.active.earth .moon {
  border: none;
  box-shadow: none;
}
ul.solarsystem li.sun {
  width: 40px;
  height: 40px;
  border-radius: 20px;
  background: #fc3;
  background-image: gradient(linear,
      left bottom,
      left top,
      color-stop(0.22, rgb(204, 153, 0)),
      color-stop(1, rgb(255, 219, 112)));
  top: 302px;
  left: 462px;
  border: none;
  box-shadow: 0 0 50px #c90;
  z-index: 100;
  transition: all 0.2s ease-in;
}
ul.solarsystem li.sun span {
  width: 60px;
  height: 60px;
  border-radius: 50%;
}
ul.solarsystem li.mercury {
  width: 100px;
  height: 100px;
  border-radius: 52px;
  top: 270px;
  left: 430px;
  z-index: 99;
}
ul.solarsystem li.mercury span {
  background: #b6bac5;
  top: 10px;
  left: 10px;
}
ul.solarsystem li.venus {
  width: 160px;
  height: 160px;
  border-radius: 82px;
  top: 240px;
  left: 400px;
  z-index: 98;
}
ul.solarsystem li.venus span {
  background: #bf8639;
  top: 118px;
  left: 5px;
}
ul.solarsystem li.earth {
  width: 220px;
  height: 220px;
  border-radius: 112px;
  top: 210px;
  left: 370px;
  z-index: 97;
}
ul.solarsystem li.earth span {
  background: #06c;
  top: 56px;
  left: 5px;
}
ul.solarsystem li.earth span.moon {
  width: 4px;
  height: 4px;
  border-radius: 2px;
  background: #ccc;
  top: 12px;
  left: 12px;
}
ul.solarsystem li.mars {
  width: 280px;
  height: 280px;
  border-radius: 142px;
  top: 180px;
  left: 340px;
  z-index: 96;
}
ul.solarsystem li.mars span {
  background: #aa4200;
  top: 0px;
  left: 175px;
}
ul.solarsystem li.asteroids_meteorids {
  top: 155px;
  left: 315px;
  z-index: 1;
  width: 330px;
  height: 330px;
  border-radius: 165px;
  border: none;
}
ul.solarsystem li.jupiter {
  width: 340px;
  height: 340px;
  border-radius: 172px;
  top: 150px;
  left: 310px;
  z-index: 95;
}
ul.solarsystem li.jupiter span {
  background: #e0ae6f;
  top: 67px;
  left: 24px;
}
ul.solarsystem li,
ul.solarsystem li.earth span {
  animation-iteration-count: infinite;
  animation-timing-function: linear;
  animation-name: orbit;
}
ul.solarsystem li.mercury {
  animation-duration: 5s;
}
ul.solarsystem li.venus {
  animation-name: retrograde;
  animation-duration: 8s;
}
ul.solarsystem li.earth {
  animation-duration: 12s;
}
ul.solarsystem li.earth span {
  animation-duration: 2s;
}
ul.solarsystem li.mars {
  animation-duration: 20s;
}
ul.solarsystem li.asteroids_meteorids {
  animation-duration: 50s;
}
ul.solarsystem li.jupiter {
  animation-duration: 30s;
}
@keyframes orbit {
  from {
    transform: rotate(0deg);
    color: white;
    font-size: 200%;
  }
  to {
    transform: rotate(360deg);
    color: black;
    font-size: 50%;
  }
}
@keyframes retrograde {
  from {
    transform: rotate(0deg);
    color: white;
    font-size: 200%;
  }
  to {
    transform: rotate(-360deg);
    color: black;
    font-size: 50%;
  }
}
</style>
<div id="animation">
<ul class="solarsystem">
  <li class="sun"><span>Sun</span></li>
  <li class="mercury"><span>Mercury</span></li>
  <li class="venus"><span>Venus</span></li>
  <li class="earth"><span>Earth<span class="moon">Moon</span></span>
  </li>
  <li class="mars"><span>Mars</span></li>
  <li class="asteroids_meteorids"><span>Asteroids</span></li>
  <li class="jupiter"><span>Jupiter</span></li>
</ul>
</div>`

document.body.insertBefore(div, root)
render(<App />, root)
```

In this demo, CSS animation is running all the time. If you use the synchronous framework such as preact or vue, you will feel obvious stuck jank.

But if you use fre or react, you can keep a consistent response, which is very important.

### Why?

As we all know, microtask clears the queue before the browser's layout, while Vue and preact update their components in microtask.

```js
// vue
this.a = 0
this.b = 1
Promise.resolve().then(updateComponent) // atter a b updated
```
They use the fetures of microtask to achieve batch updates, but also block the browser because of the feature of microtask.

In fre (or react), rendering is asynchronous, which makes use of the feature that macro tasks don't block the browser to do time slicing.

Fre fiber implements a lightweight rendering engine, which uses vdom to generate linked list, interrupts and continues in the traversal of linked list, giving the browser the chance to repaint.

### Useful?

We heard a voice that the preact and vue teams don't like time slicing. They think there are very few scenes of time slicing.

But believe me, time slicing is very useful. In addition to animation, it can also do visualization related work.

In addition, do you know the situation of react native, a non web platform? It doesn't have as good performance and memory as web. Without time slicing, animation will be difficult.

### Others

In addition to the value of time slice, its research significance is greater. Fiber rendering engine is a new exploration, there are many things to do, I need partners.

https://github.com/yisar/fre

If you have a good idea, please let me know.