This article is based on the 2021 based on the ES2021 Release Candidate.

Numeric Separators

This feature enables developers to make their numeric literals more readable by creating a visual separation between groups of digits.

1000000000   // Is this a billion? a hundred millions? Ten millions?
101475938.38 // what scale is this? what power of 10?

1_000_000_000           // Ah, so a billion
101_475_938.38          // And this is hundreds of millions

let fee = 123_00;       // $123 (12300 cents, apparently)
let fee = 12_300;       // $12,300 (woah, that fee!)
let amount = 12345_00;  // 12,345 (1234500 cents, apparently)
let amount = 123_4500;  // 123.45 (4-fixed financial)
let amount = 1_234_500; // 1,234,500

String.prototype.replaceAll

A simplified API for this common use-case that does not require RegExp knowledge. A way to global-replace strings without having to escape RegExp syntax characters.

'x'.replace('', '_');
// → '_x'
'xxx'.replace(/(?:)/g, '_');
// → '_x_x_x_'
'xxx'.replaceAll('', '_');
// → '_x_x_x_'

Logical Assignment Operators

A proposal to combine Logical Operators and Assignment Expressions.

// "Or Or Equals" (or, the Mallet operator :wink:)
a ||= b;
a || (a = b);

// "And And Equals"
a &&= b;
a && (a = b);

// "QQ Equals"
a ??= b;
a ?? (a = b);

Promise.any and AggregateError

This snippet checks which endpoint responds the fastest, and then logs it.

Promise.any([
  fetch('https://v8.dev/').then(() => 'home'),
  fetch('https://v8.dev/blog').then(() => 'blog'),
  fetch('https://v8.dev/docs').then(() => 'docs')
]).then((first) => {
  // Any of the promises was fulfilled.
  console.log(first);
  // → 'home'
}).catch((error) => {
  // All of the promises were rejected.
  console.log(error);
});

error is an AggregateError.