bvaughn

This API was removed in React 17

---

Interaction tracing with React

React recently introduced an experimental profiler API. After discussing this API with several teams at Facebook, one common piece of feedback was that the performance information would be more useful if it could be associated with the events that caused the application to render (e.g. button click, XHR response). Tracing these events (or "interactions") would enable more powerful tooling to be built around the timing information, capable of answering questions like "What caused this really slow commit?" or "How long does it typically take for this interaction to update the DOM?".

With version 16.4.3, React added experimental support for this tracing by way of a new NPM package, scheduler. However the public API for this package is not yet finalized and will likely change with upcoming minor releases, so it should be used with caution.

rauschma

Strings

String.prototype.*

None of the string methods modify this – they always return fresh strings.

• charAt(pos: number): string ^ES1

  Returns the character at index pos, as a string (JavaScript does not have a datatype for characters). str[i] is equivalent to str.charAt(i) and more concise (caveat: may not work on old engines).

elijahmanor

import React, { Component } from "react";
import { render } from "react-dom";
import "./index.css";

class Widget extends Component {
  state = { text: "" };
  handleChange = (e) => {
    this.setState({ text: e.target.value });
  };
  render() {

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

Rich-Harris

Stuff I wish I'd known sooner about service workers

I recently had several days of extremely frustrating experiences with service workers. Here are a few things I've since learned which would have made my life much easier but which isn't particularly obvious from most of the blog posts and videos I've seen.

I'll add to this list over time – suggested additions welcome in the comments or via twitter.com/rich_harris.

Use Canary for development instead of Chrome stable

Chrome 51 has some pretty wild behaviour related to console.log in service workers. Canary doesn't, and it has a load of really good service worker related stuff in devtools.

ryanflorence

function createDisabledUntilClientRendersComponent(component, displayName='ClientComponent') {
  return React.createClass({

    displayName,

    propTypes: {
      disabled: React.PropTypes.bool
    },

    getInitialState() {

iammerrick

Redux Chaos Monkey

This is a proof of concept which allows you to replay system events in a random order each time to make sure your UI can tolerate variable states.

I'm not sure if this is worthy of its on open source project with additional features like changing play back time, whitelisting/blacklisting actions etc but figured I'd put this out there to see if it piques anyones interest.

See a video of this in action here: [https://www.youtube.com/watch?v=wkoukONfwmA](Video on YouTube).

ohanhi

This is a proposal for a lightning talk at the Reactive 2015 conference.

NOTE: If you like this, star ⭐ the Gist - the amount of stars decides whether it makes the cut!

The Joy of Composition

Why stateless rendering is pure bliss

React just got stateless components, meaning that they are in essence pure functions for rendering. Pure functions make it dead simple - even fun - to refactor your views

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

ericelliott

ES6 Defaults / Overrides Pattern

Combine default parameters and destructuring for a compact version of the defaults / overrides pattern.

function foo ({
    bar = 'no',
    baz = 'works!'
  } = {}) {