Hinrich hnrchrdl

1. Create new app

npx create-react-app myapp

2. Edit workspace settings in vscode for flow typechecking

{
  "flow.useNPMPackagedFlow": true,
 "javascript.validate.enable": false

Install enzyme and enzyme react adapter

yarn add -D enzyme enzyme-react-adapter-react-16

Create a file for test setup

Create a file src/setupTests.js. It will automatically get picked up by create-react-app. In this file, put code to run before Tests. for example, to configure enzyme, put this in:

	<FeatureTypeStyle>
	<Rule>
	<PointSymbolizer>
	<Graphic>
	<Mark>
	<WellKnownName>circle</WellKnownName>
	<Fill>
	<CssParameter name="fill">#FF0000</CssParameter>
	</Fill>
	</Mark>

	<?xml version="1.0" encoding="utf-8"?>
	<configuration>
	<system.web>
	<httpRuntime maxQueryStringLength="32768" maxUrlLength="65536"/>
	</system.web>
	<system.webServer>
	<security>
	<requestFiltering>
	<requestLimits maxQueryString="32768"/>
	</requestFiltering>

	=== install deps ===
	sudo apt update
	sudo apt install zsh fonts-powerline wget git

	=== change default shell ===
	chsh -s /bin/zsh

	=== (optional) verify installation ===
	which zsh -> 'usr/bin/zsh'
	echo $SHELL -> 'usr/bin/zsh'

	const App = () => {
	const [counter, setCounter] = useState(0);
	const [aboveFive, setAboveFive] = useState(false);

	const increment = () => {
	setCounter(n => n + 1);
	};

	useEffect(() => {
	if (counter > 5) {

	const Child = React.memo(({ isAboveFive, children }) => {
	console.log("child renders");
	return (
	<>
	<h2>Child: {!isAboveFive ? "<= 5" : "> 5"}</h2>
	{children}
	</>
	);
	});

	shouldComponentUpdate(prevProps) {
	return prevProps.isAboveFive !== this.props.isAboveFive;
	}