chun shang springuper

any: magic, ill-behaved type that acts like a combination of never (the proper [bottom type]) and unknown (the proper [top type])
- Anything except never is assignable to any, and any is assignable to anything at all.
- Identities: any & AnyTypeExpression = any, any | AnyTypeExpression = any
- Key TypeScript feature that allows for [gradual typing].
unknown: proper, well-behaved [top type]
- Anything at all is assignable to unknown. unknown is only assignable to itself (unknown) and any.
- Identities: unknown & AnyTypeExpression = AnyTypeExpression, unknown | AnyTypeExpression = unknown

Prefer over any whenever possible. Anywhere in well-typed code you're tempted to use any, you probably want unknown.

Profiler

React 16.4 will introduce a new Profiler component (initially exported as React.unstable_Profiler) for collecting render timing information in order to measure the "cost" of rendering for both sync and async modes.

Profiler timing metrics are significantly faster than those built around the User Timing API, and as such we plan to provide a production+profiling bundle in the future. (The initial release will only log timing information in DEV mode, although the component will still render its children- without timings- in production mode.)

How is it used?

Profiler can be declared anywhere within a React tree to measure the cost of rendering that portion of the tree. For example, a Navigation component and its descendants:

Tech Lead Book

Introduction
What is a Tech Lead?
The Tech Lead Mindset
Becoming a Tech Lead
Working Cross-Functionally
The Art of Delegation
Technical Best Practices
Effective Decision Making

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

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.

Web Components Resources

Specs / standardization

W3C Introduction to Web Components - explainer/overview of the technologies

5 entertaining things you can find with the GitHub Search API

Let's have some command-line fun with curl, [jq][1], and the [new GitHub Search API][2].

Today we're looking for:

The hottest repositories created in the last week.
The oldest user accounts with zero followers. (So sad.)
Issue trends by language.
Clojure projects defying convention.

	import React from "react";

	const context = React.createContext();

	export function QueryClientProvider({ children, client }) {
	React.useEffect(() => {
	const onFocus = () => {
	client.queries.forEach((query) => {
	query.subscribers.forEach((subscriber) => {
	subscriber.fetch();

	const Cont = require('./lazy-continuation');

	// pointed version
	const c = Cont.of(5) // initial value
	.chain((x) => {
	return Cont.of(x + 5); // synchronous computation
	})
	.chain((x) => { // async computation
	return new Cont((resolve) => {
	setTimeout(() => resolve(x + 15), 500);

	Handlebars is a semantic web template system, started by Yehuda Katz in 2010.
	Handlebars.js is a superset of Mustache, and can render Mustache templates in addition to Handlebars templates.
	More: http://handlebarsjs.com/


	1. Expressions.

	1.1 Basic usage.