New JavaScript Proposals: Error.isError, RegExp.escape, Uint8Array Base64

When a proposal reaches Stage 3, browsers and Node.js begin implementing its features, and changes are rare unless major issues arise.

Error.isError

Proposal address: proposal-is-error This proposal introduces a global method Error.isError to accurately determine whether an object is an Error type.

The need arises because Symbol.toStringTag can make Object.prototype.toString() return unreliable values.

By creating a fake error class that returns 'Error' from its [Symbol.toStringTag], the Object.prototype.toString.call output becomes [object Error]:

class FakeError {
  get [Symbol.toStringTag]() {
    return 'Error';
  }
}
// Output: [object Error]
console.log(Object.prototype.toString.call(new FakeError()));
// Output: [object Error]
console.log(Object.prototype.toString.call(new Error()));
// Output: true
console.log(Object.prototype.toString.call(new Error()) === Object.prototype.toString.call(new FakeError()))

The widely used is-error package (30 w weekly downloads) implements this check with Object.prototype.toString() === '[object Error]'.

RegExp.escape

Proposal address: proposal-regex-escaping Developers often need to build regular expressions from strings without treating special characters as regex tokens, but JavaScript lacks a built‑in way to escape them safely.

let text = "Hello.";
// this would match . against any character rather than matching it against a dot
ourLongText.replace(new RegExp(text, "g"))

When user input is used to construct a regex, it must be escaped first to avoid security issues. Existing escape implementations may miss some special characters or mishandle multi‑code‑unit UTF‑8 characters (e.g., '😂'.length === 2), creating maintenance burdens.

const str = prompt("Please enter a string");
const escaped = RegExp.escape(str);
const re = new RegExp(escaped, 'g'); // handles regex special tokens with the replacement.
console.log(ourLongText.replace(re));

This proposal adds a RegExp.escape function that escapes all characters with special regex meaning.

RegExp.escape("The Quick Brown Fox"); // "The Quick Brown Fox"
RegExp.escape("Buy it. use it. break it. fix it."); // "Buy it\. use it\. break it\. fix it\."
RegExp.escape("(*.*)"); // "\(\*\.\*\)"
RegExp.escape("｡^･ｪ･^｡"); // "｡\^･ｪ･\^｡"
RegExp.escape("😊 *_* +_+ ... 👍"); // "😊 \*_* \+_+ \.\.\. 👍"
RegExp.escape("\d \D (?:)"); // "\\d \\D \(\?:\)"

Uint8Array to/from base64 and hex

Proposal address: proposal-arraybuffer-base64 The proposal aims to add support for converting binary data in Uint8Array to and from Base64 (and hex) directly.

JavaScript currently provides btoa and atob for string‑Base64 conversion, which can be used with binary data but are limited to the Latin‑1 range (0x00‑0xFF).

const binaryData = new Uint8Array([72,101,108,108,111,44,32,87,111,114,108,100,33]);
// binary data → Base64
const base64Data = btoa(String.fromCharCode.apply(null, binaryData));
console.log(base64Data); // "SGVsbG8sIFdvcmxkIQ=="
// Base64 → binary data
const decodedBinaryData = new Uint8Array(atob(base64Data).split('').map(function(c) {
  return c.charCodeAt(0);
}));
console.log(decodedBinaryData); // Uint8Array[ 72,101,108,108,111,44,32,87,111,114,108,100,33 ]

Because atob and btoa are limited to Latin‑1, a more general binary conversion capability is needed. The proposal introduces Uint8Array.prototype.toBase64 and Uint8Array.fromBase64 for direct conversion:

const raw = new Uint8Array([72,101,108,108,111,32,87,111,114,108,100]);
const str = raw.toBase64(); // 'SGVsbG8gV29ybGQ='
const arr = Uint8Array.fromBase64(str); // Uint8Array([72,101,108,108,111,32,87,111,114,108,100])

The proposal also adds Uint8Array.prototype.toHex and Uint8Array.fromHex for hex conversion.

Time Zone Canonicalization

Proposal address: proposal-canonical-tz ECMAScript time‑zone names come from the IANA Time Zone Database and are periodically updated, requiring developers to keep their zone identifiers current. This proposal standardizes handling of updated zones, simplifies identifiers, and introduces Temporal.TimeZone.prototype.equals to check if two zones refer to the same location.

Temporal.TimeZone.from('Asia/Calcutta').equals('Asia/Kolkata');
// => true