jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

staltz

The introduction to Reactive Programming you've been missing

(by @andrestaltz)

---

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

---

cvrebert

Test apparatus: http://jsfiddle.net/hRub4/

(Windows = Windows 8.1 desktop)

• Windows Chrome 39
  • Button focuses on click and via keyboard tabbing
  • Anchor focuses on click and via keyboard tabbing
• Windows Firefox 30.0
  • Button focuses on click and via keyboard tabbing
  • Anchor focuses on click and via keyboard tabbing
• Windows Internet Explorer 11

paulirish

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

markerikson

// See https://blog.isquaredsoftware.com/presentations/react-redux-ts-intro-2020-12/#/36 for slides
// My basic render function structure:
function RenderLogicExample({
  someBoolean, // 1) Destructure values from `props` object
  someList,
}) {
  // 2) Declare state values
  const [a, setA] = useState(0);
  const [b, setB] = useState(0);

VictorTaelin

async/await is just the do-notation of the Promise monad

CertSimple just wrote a blog post arguing ES2017's async/await was the best thing to happen with JavaScript. I wholeheartedly agree.

In short, one of the (few?) good things about JavaScript used to be how well it handled asynchronous requests. This was mostly thanks to its Scheme-inherited implementation of functions and closures. That, though, was also one of its worst faults, because it led to the "callback hell", an seemingly unavoidable pattern that made highly asynchronous JS code almost unreadable. Many solutions attempted to solve that, but most failed. Promises almost did it, but failed too. Finally, async/await is here and, combined with Promises, it solves the problem for good. On this post, I'll explain why that is the case and trace a link between promises, async/await, the do-notation and monads.

First, let's illustrate the 3 styles by implementing

ericls

// Use hacker news API as example
async function getData() {
  const ids = await (await fetch('https://hacker-news.firebaseio.com/v0/topstories.json')).json()
  const data = Promise.all(
    ids.map(async (i) => await (await fetch(`https://hacker-news.firebaseio.com/v0/item/${i}.json?print=pretty`)).json())
  )
  return data
}

getData()

sebmarkbage

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

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.

joshwcomeau

/**
`useChangeLog` - dev-mode helper hook to let you 
know why a memoized component re-rendered!


Usage example:

const YourComponent = React.memo((props) => {
  // Just drop this fella into your memo component's body.
  useChangeLog(props);