Lihour lihourchhin

Advanced memoization and effects in React

Memoization is a somewhat fraught topic in the React world, meaning that it's easy to go wrong with it, for example, by [making memo() do nothing][memo-pitfall] by passing in children to a component. The general advice is to avoid memoization until the profiler tells you to optimize, but not all use cases are general, and even in the general use case you can find tricky nuances.

Discussing this topic requires some groundwork about the technical terms, and I'm placing these in once place so that it's easy to skim and skip over:

Memoization means caching the output based on the input; in the case of functions, it means caching the return value based on the arguments.
Values and references are unfortunately overloaded terms that can refer to the low-level implementation details of assignments in a language like C++, for example, or to memory

Introduction

Docker.app will complain about incompatible processor, so we will use Docker Machine.

Instalation

Download Docker for Mac (Docker.app). It contains some binaries that are necessary.

brew install virtualbox docker-machine

Installing Postgres via Brew

Pre-Reqs

Brew Package Manager

In your command-line run the following commands:

brew doctor
brew update

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Generally, all APIs that synchronously provide layout metrics will trigger forced reflow / layout. Read on for additional cases and details.

Element APIs

Getting box metrics

elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent

	package com.cubetiqs.factory

	import org.junit.jupiter.api.Assertions
	import org.junit.jupiter.api.Test

	class FactoryTests {

	@Test
	fun factoryTest() {
	val carA = CarFactory(CarType.CAR_A).getCar()

	package com.cubetiqs.factory

	import org.junit.jupiter.api.Assertions
	import org.junit.jupiter.api.Test

	class FactoryTests {

	@Test
	fun factoryTest() {
	val carA = CarFactory(CarType.CAR_A).getCar()

	class FetchDataFromRSSFeed extends Component {
	constructor() {
	super();
	this.state = {
	recentBlogPost: {
	name: '',
	url: ''
	}
	}
	}

	/*
	* Handling Errors using async/await
	* Has to be used inside an async function
	*/
	try {
	const response = await axios.get('https://your.site/api/v1/bla/ble/bli');
	// Success 🎉
	console.log(response);
	} catch (error) {
	// Error 😨

	# The initial version
	if [ ! -f .env ]
	then
	export $(cat .env \| xargs)
	fi

	# My favorite from the comments. Thanks @richarddewit & others!
	set -a && source .env && set +a

	## Pre-requisite: You have to know your last commit message from your deleted branch.
	git reflog
	# Search for message in the list
	# a901eda HEAD@{18}: commit: <last commit message>

	# Now you have two options, either checkout revision or HEAD
	git checkout a901eda
	# Or
	git checkout HEAD@{18}