Domenic Denicola domenic

The following are currently exposed to windows and workers. They are not exposed to worklets, but in Domenic's opinion, should be:

AbortController
AbortSignal (except AbortSignal.timeout)
addEventListener
atob
btoa
crypto.getRandomValues
CompressionStream
CustomEvent

Generic zero-copy ArrayBuffer usage

Most APIs which accept binary data need to ensure that the data is not modified while they read from it. (Without loss of generality, let's only analyze ArrayBuffer instances for now.) Modifications can come about due to the API processing the data asynchronously, or due to the API processing the data on some other thread which runs in parallel to the main thread. (E.g., an OS API which reads from the provided ArrayBuffer and writes it to a file.)

On the web platform, APIs generally solve this by immediately making a copy of the incoming data. The code is essentially:

function someAPI(arrayBuffer) {
  arrayBuffer = arrayBuffer.slice(); // make a copy

Two origins, A and B, are said to be same site if the following returns true:

Let siteA be the result of obtaining a site from A.
Let siteB be the result of obtaining a site from B.
Return true if siteA equals siteB.

Two origins, A and B, are said to be schemelessly-same site if the following returns true:

Let siteA be the result of obtaining a site from A.
Let siteB be the result of obtaining a site from B.

ToString() in JavaScript

I am posting this as a gist because I am too lazy to figure out my blog. TODO: move it to https://domenic.me/ one day.

A lot of specifications use the ToString() abstract operation. (What's an abstract operation?) For example, any web specification which uses Web IDL's DOMString type (i.e., its basic string type) will convert incoming values using ToString(). Similarly, various parts of the JS specification itself perform ToString(). One example is the Error constructor, which we will refer to going forward.

If you are trying to implement or polyfill such a specification in JavaScript, how do you do it? For example, given

function ErrorConstructorPolyfill(message) {

Context: tc39/proposal-set-methods#50

Proposed spec texts

Set.prototype.difference(arg), minimalist

If Type(this) is not Object, or this does not have a [[SetData]] internal slot, throw a new TypeError exception.
If Type(arg) is not Object, or arg does not have a [[SetData]] internal slot, throw a new TypeError exception.
Let diffList be a List containing all elements that are in this.[[SetData]] but are not in arg.[[SetData]], using SameValueZero to determine identity. (Optional: formalize this with a loop that operates on the Lists.)
Let newSet be ? OrdinaryCreateFromConstructor(%Set%, "%SetPrototype%", « [[SetData]] »).

Obtaining a resource from a link element

All [external resource links] have an algorithm to fetch and process the linked resource.

Individual link types may define their own [fetch and process the linked resource] algorithm, which takes the link element el. But if not otherwise stated, they use the following default fetch and process the linked resource algorithm, given el:

If el's href attribute's value...
... stuff ...
Fetch request. To process response given the response response:
Let success be true.

	"use strict";
	const { URL } = require(".");

	const inputs = [
	"https://\u0000y",
	"https://x/\u0000y",
	"https://x/?\u0000y",
	"https://x/?#\u0000y"
	];

	import { languagesSet } from "./some-library.mjs";

	// Allowed
	languagesSet.keys();
	languagesSet.entries();
	languagesSet.forEach(l => console.log);
	languagesSet.size;
	languagesSet.values();

	// Will throw TypeError

	// This is a minimal UA sniffer, that only cares about the rendering/JS engine
	// name and version, which should be enough to do feature discrimination and
	// differential code loading.
	//
	// This is distinct from things like https://www.npmjs.com/package/ua-parser-js
	// which distinguish between different branded browsers that use the same rendering
	// engine. That sort of distinction is maybe useful for analytics purposes, but
	// for differential code loading it is overcomplicated.
	//
	// This is meant to demonstrate that UA sniffing is not really that hard if you're

	<!DOCTYPE HTML>
	<html lang="en">
	<meta charset="utf-8">
	<title>Working Mode — WHATWG</title>
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta name="theme-color" content="#3A7908">
	<link rel="icon" href="https://resources.whatwg.org/logo.svg">
	<link rel="stylesheet" href="/style/shared.css">
	<link rel="stylesheet" href="/style/subpages.css">