Node.js 15.x: What's New, Release History & Support Lifecycle

What Is New in Node.js 15?

Unhandled Promise Rejections Now Crash the Process

In Node.js 15, an unhandled promise rejection terminates the process with a non-zero exit code by default. Previously this was a warning. This is the most impactful breaking change in v15 and affects any code where rejected promises are not caught.

// This will now CRASH the process in Node.js 15+
async function fail() {
  throw new Error('oops');
}
fail(); // no await, no .catch() -- EXIT 1

// Fix: always handle rejections
fail().catch(console.error);
// or:
process.on('unhandledRejection', (err) => { /* log + exit */ });

This forces better error handling discipline but will expose existing bugs in codebases that silently ignored rejected promises.

String.replaceAll() and Promise.any()

String.prototype.replaceAll() replaces all occurrences of a substring without a regex. Promise.any() resolves as soon as the first promise in the iterable fulfills -- the inverse of Promise.race() for success cases.

// No more regex for global replace
'foo-bar-baz'.replaceAll('-', '_'); // 'foo_bar_baz'

// First successful result
const result = await Promise.any([fetchA(), fetchB(), fetchC()]);

Logical Assignment Operators

Three new operators landed: &&=, ||=, and ??=. They combine logical evaluation with assignment, reducing boilerplate for common patterns like setting defaults.

let config = { retries: null };
config.retries ??= 3;       // sets to 3 because null
config.timeout ||= 5000;    // sets to 5000 because falsy
config.debug &&= verbose;   // assigns verbose only if config.debug is truthy

Experimental Web Crypto API

The Web Cryptography API (globalThis.crypto) lands experimentally in Node.js 15. You can use it to generate keys, sign data, hash values, and derive secrets using the same API as browsers -- without importing node:crypto.