Updates from the 105th TC39 meeting

There were several items on the agenda, this post focuses on feature proposals and their progress from the 105th TC39 meeting [2th-5th December 2024].

Stage 4

• Intl.DurationFormat Provides a way to format a duration (e.g., "1 hour, 30 minutes") in a locale-sensitive manner.

new Intl.DurationFormat("fr-FR", { style: "long" }).format({
    hours: 1,
    minutes: 46,
    seconds: 40,
});
// => "1 heure, 46 minutes et 40 secondes"

Stage 3

• Error.isError Adds a static isError method to check whether a given value is an instance of the Error object.

Error.isError(undefined); // false
Error.isError(isError(new Error()); // true

Stage 2.7

• ESM Phase Imports Enhances the ECMAScript Module (ESM) system with new import capabilities to streamline inter-module dependency declarations.

import source myModule from "./my-module.js";

// `{ type: 'module' }` can be inferred since myModule is a module object
const worker = new Worker(myModule);

P.S: Note this is a conditional approval.

Stage 2

• Immutable ArrayBuffer Introduces the concept of immutable ArrayBuffer to prevent mutation of binary data after creation.

Object.freeze(new Uint8Array(buf.transferToImmutable()));

• Intl Currency Display Choices Expands options for displaying currency values, such as adding control over currency symbols and code styles.

const formal = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
  currencyDisplay: "formalSymbol",
});
formal.format(42); // "US$42.00"

const never = new Intl.NumberFormat("en-US", {
  style: "currency",
  currency: "USD",
  currencyDisplay: "never",
});
never.format(42); // "42.00"

Stage 1

• Import Sync An explicit synchronous import function for ES modules, building on the synchronous execution behavior defined by the Defer Import Eval proposal.

let react;
try {
  react = import.sync('react');
} catch {}

if (react) {
  // Bind to the React framework, if available
}

• Stabilize New integrity "level" protecting against both override mistakes and proxy reentrancy