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I heard some points of criticism to how React deals with reactivity and it's focus on "purity". It's interesting because there are really two approaches evolving. There's a mutable + change tracking approach and there's an immutability + referential equality testing approach. It's difficult to mix and match them when you build new features on top. So that's why React has been pushing a bit harder on immutability lately to be able to build on top of it. Both have various tradeoffs but others are doing good research in other areas, so we've decided to focus on this direction and see where it leads us.

I did want to address a few points that I didn't see get enough consideration around the tradeoffs. So here's a small brain dump.

"Compiled output results in smaller apps" - E.g. Svelte apps start smaller but the compiler output is 3-4x larger per component than the equivalent VDOM approach. This is mostly due to the code that is usually shared in the VDOM "VM" needs to be inlined into each component. The tr

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/**
 * Basic proof of concept.
 * - Hot reloadable
 * - Stateless stores
 * - Stores and action creators interoperable with Redux.
 */

import React, { Component } from 'react';

export default function dispatch(store, atom, action) {

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React recently introduced an experimental profiler API. This page gives instructions on how to use this API in a production release of your app.

Table of Contents

• Profiling in production
  • Create React App
  • Webpack 4
• Troubleshooting
  • Tracing broke after an NPM update

Profiling in production

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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.

This Gist provides some high-level docum

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Algebraic Effects in JavaScript part 2 - Capturing continuations with Generators

This is the second part of a series about Algebraic Effects and Handlers.

• Part 1 : continuations and control transfer
• Part 2 : Capturing continuations with Generators
• Part 3 : Delimited continuations
• Part 4 : Algebraic Effects and handlers

Note: initially I planned a 3-part series, but since the current post on undelimited continuations ended up taking

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// We model the call stack using a linked list of Generators
// Each Generator has a _return field pointing back to its parent

function stepGen(gen, arg) {
    const {done, value} = gen.next(arg)
    if(done) {        
        if(gen._return) {
            stepGen(gen._return, value)
        }

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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.

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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).

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javascript:(function(){if(window._activeElInterval){clearInterval(window._activeElInterval);delete window._activeElInterval;}else{var activeEl;window._activeElInterval=setInterval(function(){var currentActiveEl=document.activeElement;if(currentActiveEl!==activeEl){activeEl=currentActiveEl;console.log(activeEl);}},200);}})();

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script to kill apache 1.3 / 2.x prefork httpd processes serving preconnect connections, in an attempt to prevent chrome from causing a DoS against the httpd

This is version 2 of https://gist.github.com/eqhmcow/4774549

The major change is the use of two processes instead of one:

One process makes server-status requests, the other kills idle prefork processes.

This allows the kill script to continue killing idle processes even when Chrome has effectively DoS'd the apache server. When this happens, the check script can't get an updated status response back immediately, but the kill script can hopefully free up a slot by killing some processes. Having an uninterrupted request in the socket queue allows us to get an updated response after killing the Chrome preconnections are killed.