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.

jlengstorf

Create Custom git.io Short Links

Add this helper function to your ~/.bash_profile (or ~/.bashrc, or whatever you use) to create custom short links for your GitHub projects without having to remember the whole cURL command!

Installation

If you use a file other than ~/.bash_profile to configure your terminal, substitute that value in the installation instructions below.

1. Open your ~/.bash_profile
2. Copy-paste the gitlink function into it

bvaughn

// This is an example of how to fetch external data in response to updated props,
// If you are using an async mechanism that does not support cancellation (e.g. a Promise).

class ExampleComponent extends React.Component {
  _currentId = null;

  state = {
    externalData: null
  };

bvaughn

// This is an advanced example! It is not intended for use in application code.
// Libraries like Relay may make use of this technique to save some time on low-end mobile devices.
// Most components should just initiate async requests in componentDidMount.

class ExampleComponent extends React.Component {
  _hasUnmounted = false;

  state = {
    externalData: null,
  };

ljharb

Array Iteration

https://gist.github.com/ljharb/58faf1cfcb4e6808f74aae4ef7944cff

While attempting to explain JavaScript's reduce method on arrays, conceptually, I came up with the following - hopefully it's helpful; happy to tweak it if anyone has suggestions.

Intro

JavaScript Arrays have lots of built in methods on their prototype. Some of them mutate - ie, they change the underlying array in-place. Luckily, most of them do not - they instead return an entirely distinct array. Since arrays are conceptually a contiguous list of items, it helps code clarity and maintainability a lot to be able to operate on them in a "functional" way. (I'll also insist on referring to an array as a "list" - although in some languages, List is a native data type, in JS and this post, I'm referring to the concept. Everywhere I use the word "list" you can assume I'm talking about a JS Array) This means, to perform a single operation on the list as a whole ("atomically"), and to return a new list - thus making it mu

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

BenMorel

/**
 * Fix for vw, vh, vmin, vmax on iOS 7.
 * http://caniuse.com/#feat=viewport-units
 *
 * This fix works by replacing viewport units with px values on known screen sizes.
 *
 * iPhone 6 and 6 Plus cannot run iOS 7, so are not targeted by this fix.
 * Target devices running iOS 8+ will incidentally execute the media query,
 * but this will still produce the expected result; so this is not a problem.

JamesMessinger

// This works on all devices/browsers, and uses IndexedDBShim as a final fallback 
var indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB || window.shimIndexedDB;

// Open (or create) the database
var open = indexedDB.open("MyDatabase", 1);

// Create the schema
open.onupgradeneeded = function() {
    var db = open.result;
    var store = db.createObjectStore("MyObjectStore", {keyPath: "id"});

paulirish

/* bling.js */

window.$ = document.querySelectorAll.bind(document);

Node.prototype.on = window.on = function (name, fn) {
  this.addEventListener(name, fn);
};

NodeList.prototype.__proto__ = Array.prototype;

addyosmani

CSS Layout Debugger

A tweet-sized debugger for visualizing your CSS layouts. Outlines every DOM element on your page a random (valid) CSS hex color.

One-line version to paste in your DevTools

Use $$ if your browser aliases it:

~ 108 byte version