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Sebastian Markbåge sebmarkbage

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sebmarkbage / The Rules.md
Last active Oct 24, 2020
The Rules of React
View The Rules.md

The Rules of React

All libraries have subtle rules that you have to follow for them to work well. Often these are implied and undocumented rules that you have to learn as you go. This is an attempt to document the rules of React renders. Ideally a type system could enforce it.

What Functions Are "Pure"?

A number of methods in React are assumed to be "pure".

On classes that's the constructor, getDerivedStateFromProps, shouldComponentUpdate and render.

@sebmarkbage
sebmarkbage / Enhance.js
Last active Oct 16, 2020
Higher-order Components
View Enhance.js
import { Component } from "React";
export var Enhance = ComposedComponent => class extends Component {
constructor() {
this.state = { data: null };
}
componentDidMount() {
this.setState({ data: 'Hello' });
}
render() {
View Infrastructure.js
let cache = new Map();
let pending = new Map();
function fetchTextSync(url) {
if (cache.has(url)) {
return cache.get(url);
}
if (pending.has(url)) {
throw pending.get(url);
}
@sebmarkbage
sebmarkbage / SubscriptionIsHard.js
Last active Oct 11, 2020
Subscription Is Hard?
View SubscriptionIsHard.js
class SubscriptionDoneRight extends Component {
state = {
data: Store.read(props.id)
}
getDerivedStateFromProps(props, state) {
return {
data: Store.read(props.id),
};
}
@sebmarkbage
sebmarkbage / WhyReact.md
Created Sep 4, 2019
Why is React doing this?
View WhyReact.md

I heard some points of criticism to how React deals with reactivity and it's focus on "purity". It's interesting because there are really two approaches evolving. There's a mutable + change tracking approach and there's an immutability + referential equality testing approach. It's difficult to mix and match them when you build new features on top. So that's why React has been pushing a bit harder on immutability lately to be able to build on top of it. Both have various tradeoffs but others are doing good research in other areas, so we've decided to focus on this direction and see where it leads us.

I did want to address a few points that I didn't see get enough consideration around the tradeoffs. So here's a small brain dump.

"Compiled output results in smaller apps" - E.g. Svelte apps start smaller but the compiler output is 3-4x larger per component than the equivalent VDOM approach. This is mostly due to the code that is usually shared in the VDOM "VM" needs to be inlined into each component. The tr

@sebmarkbage
sebmarkbage / react-terminology.md
Last active Oct 2, 2020
React (Virtual) DOM Terminology
View react-terminology.md
View es6mixin.js
var Bar1 = base => class extends base {
componentWillMount(){
super.componentWillMount();
console.log('Bar1');
}
};
var Bar2 = base => class extends base {
componentWillMount(){
super.componentWillMount();
@sebmarkbage
sebmarkbage / JSXSpreadAttributes.md
Last active Aug 13, 2020
JSX Spread Attributes
View JSXSpreadAttributes.md

JSX Spread Attributes

If you know all the properties that you want to place on a component a head of time, it is easy to use JSX:

  var component = <Component foo={x} bar={y} />;

Mutating Props is Bad, mkay

@sebmarkbage
sebmarkbage / API.js
Last active Aug 11, 2020
Custom Stack Frames
View API.js
type FrameScope = {
[key:string]: mixed
};
type StackFrame = {
name?: string,
fileName?: string,
lineNumber?: number,
columnNumber?: number,
scope?: FrameScope
};
View ReactCanvasDrawing.js
/** @jsx React.DOM */
var Graphic = React.createClass({
componentDidMount: function() {
var context = this.getDOMNode().getContext('2d');
this.paint(context);
},
componentDidUpdate: function() {
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