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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

A better GeoJSON

GeoJSON is a widely-used format for encoding geographic data. It's flexible and human-readable, and because it's just JSON it's easy to integrate into web applications.

But it has some real warts, and if we wanted to we could certainly come up with a better format. After tweeting about my frustrations, I was asked to elaborate. Here goes:

Redundancy

GeoJSON geometries can be one of seven types: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon and GeometryCollection.

	import SimpleHTTPServer
	class CORSHTTPRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
	def send_head(self):
	"""Common code for GET and HEAD commands.

	This sends the response code and MIME headers.

	Return value is either a file object (which has to be copied
	to the outputfile by the caller unless the command was HEAD,
	and must be closed by the caller under all circumstances), or

	import { h, Component } from 'preact';
	import Markup from 'preact-markup';
	import register from './preact-custom-element';

	// just a proxy component: WC -> Preact -> WC
	const A = () => <x-b foo="initial foo from <x-a>" />;

	// stateful component that can re-render
	class B extends Component {
	render(props, state) {

	type HTMLElementPrototype = HTMLElement extends { prototype: infer Prototype }
	? Prototype
	: never;

	declare namespace h {
	namespace JSX {
	interface Element {}
	type LibraryManagedAttributes<E, _> = E extends {
	prototype: infer Prototype;
	}

	import fetch from 'node-fetch';

	export async function requestSnapshot(url, data) {

	const response = await fetch('https://little-paper-d118.bkardell.workers.dev', {
	method: 'POST',
	mode: 'no-cors',
	headers: {url: url}
	});

	/* JSON XPath search */ (await import('https://unpkg.com/espath')).default(window.dataLayer, '//string')

	/* cookie to object */ Object.fromEntries(document.cookie.split('; ').map(entry => entry.split('=')))

	/* cookie to object */ (await import('https://v2.crocdn.com/_plugins/cookie-to-object.js')).default()

	/* css elements search / document.querySelectorAll ('')

	/* xpath element search / (await import('https://unpkg.com/queryxpath/queryxpath.es.js')).queryXPathAll ('//')

	$URI = "/catalog-service/api/consumer/resourceViews/?withExtendedData=$($WithExtendedData)&withOperations=$($WithOperations)&managedOnly=$($ManagedOnly)&`$orderby=name asc&limit=$($Limit)&page=$($page)&`$filter=resourceType/id eq 'Infrastructure.Machine' or resourceType/id eq 'Infrastructure.Virtual' or resourceType/id eq 'Infrastructure.Cloud' or resourceType/id eq 'Infrastructure.Physical'"

	$EscapedURI = [uri]::EscapeUriString($URI)

	$Response = Invoke-vRARestMethod -Method GET -URI $EscapedURI -Verbose:$VerbosePreference

	function camelToKebab(string) {
	const tag = document.createElement('span')
	tag.dataset[string] = true
	return tag.attributes[0].name.split(/^data-/)[1]
	}

	let _str = (function(){
	const tag = document.createElement('span')
	return {
	propToAttr: (string) {
	tag.dataset[string] = true
	return tag.attributes[0].name.split(/^data-/)[1]
	},
	attrToProp(string) {
	tag.setAttribute(`data-${string}`, true)
	return Object.entries(tag.dataset)[0][0]