ES2021: The Features Worth Adopting Today

ES2021 is a small release, but three of its features immediately replaced utility code in my projects.

String.prototype.replaceAll

No more regex-with-global-flag for simple substring replacement:

"2021-01-14".replaceAll("-", "/");  // "2021/01/14"

// Before: "2021-01-14".replace(/-/g, "/") — and everyone forgot
// that .replace("-", "/") only hits the first occurrence

Logical assignment operators

||=, &&=, and ??= combine logic with assignment:

// Set a default only if the value is null/undefined
options.timeout ??= 5000;

// Before
options.timeout = options.timeout ?? 5000;

??= is the star: perfect for defaulting config objects without clobbering legitimate falsy values like 0 or false.

Promise.any

Resolves with the first fulfilled promise, ignoring rejections until all fail:

const fastest = await Promise.any([
  fetch("https://cdn-eu.example.com/data.json"),
  fetch("https://cdn-us.example.com/data.json"),
]);

This is the racing-mirrors pattern. Promise.race would reject if the first settled promise rejects; Promise.any keeps waiting for a success. If everything fails you get an AggregateError with all the reasons.

Numeric separators

Pure readability:

const budget = 1_000_000;
const bytes = 0xFF_FF_FF_FF;

Support status

Chrome 85+, Firefox 79+ (replaceAll 77+), Safari 14+ cover all of it. For older targets, @babel/preset-env with the right browserslist handles the transforms. These are the kind of features you can adopt in an afternoon — update your lint config (es2021: true in ESLint env) and start deleting utility functions.