Justin Fagnani justinfagnani

This is a reproduction for https://bugs.chromium.org/p/chromium/issues/detail?id=1050221

To reproduce:

Download gist
run npm i
run npm start

Chrome will start, cycle through some async tasks, and print the duration to the document and the terminal running node. On my laptop it takes ~500ms.

Next, run npm start again, bug switch back to the terminal as soon as Chrome launches. There should be enough time to put Chrome in the background before the task completes. The tasks should either never start or never complete. If you put Chrome in the foreground, the tasks will finish quickly.

Preemptible JavaScript Functions

Can we allow JS functions to opt-in to be prempted?

Synchronous

An expensive synchronous function will jank the UI:

function expensive() {}

	import type {ReactiveController, ReactiveControllerHost} from 'lit';

	/**
	* A reactive controller that updates a host when slotted content changes and
	* provides helper methods for checking and getting assigned slot content.
	*/
	export class SlotController implements ReactiveController {
	private _host: ReactiveControllerHost & Element;
	private _slotNames?: ReadonlyArray<string>;

	import {ApolloClient, NormalizedCacheObject} from '@apollo/client/core';

	/**
	* Fired when an Apollo controller is connected to the document tree via its
	* host. Listeners should supply an Apollo client by setting the `client`
	* property on the event.
	*/
	export class ApolloControllerConnectedEvent extends Event {
	static readonly eventName = 'apollo-controller-connected';

	class ExampleElement extends ObservableLitElement {

	@property()
	src: string;

	@observe('src')
	protected async _onSrcChange() {
	// fetch the new URL...
	}
	}

	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8"/>
	<title>Creating an TreeWalker, DOM element, and setting a walker's currentNode #jsbench #jsperf</title>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/benchmark/1.0.0/benchmark.min.js"></script>
	<script src="./suite.js"></script>
	</head>
	<body>
	<h1>Open the console to view the results</h1>

	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8"/>
	<title>Directive Implementations</title>
	<script src="https://cdnjs.cloudflare.com/ajax/libs/benchmark/1.0.0/benchmark.min.js"></script>
	<script src="./suite.js"></script>
	</head>
	<body>
	<h1>Open the console to view the results</h1>

	import lottie from './lib/lottie-import.js';

	export class LottiePlayerElement extends HTMLElement {

	get src(): string \| null {
	return this.getAttribute('src');
	}

	set src(v: string \| null) {
	if (v == null) {

	import {LitElement, html} from 'lit-element';
	import {UseWindowSize} from './useWindowSize.js';

	class extends UseWindowSize()(LitElement) {
	render() {
	return html`
	<p>
	width: ${window.innerWidth}
	height: ${window.innerHeight}
	</p>