Node.js 19.x: What's New, Release History & Support Lifecycle

What Is New in Node.js 19?

HTTP Keep-Alive On by Default -- What This Means for You

All HTTP and HTTPS clients now set keep-alive: true in their default agent. Prior to v19, each request spun up a new TCP connection unless you explicitly configured an agent with keepAlive: true.

This noticeably improves throughput for microservices that make many rapid HTTP calls to the same upstream. In practice, you'll see lower latency and fewer TIME_WAIT sockets in high-frequency call patterns -- no code changes required.

Built-in Watch Mode

Run Node.js with --watch and the process restarts automatically when the entry file or any of its dependencies change on disk. No nodemon required for development loops.

node --watch server.js
# or watch a specific file
node --watch-path=./src server.js

The implementation uses fs.watch internally. It's experimental in v19, but functional enough for most dev workflows. Production use is not recommended -- use a process manager there instead.

ESM Loader Hooks in a Separate Thread

Custom ESM loader hooks (--loader or --experimental-loader) now run off the main thread. This prevents hook code from blocking the main event loop and resolves a class of deadlock issues when hooks perform async operations during module loading.

This is a breaking behavior change for loaders that rely on shared mutable state between the hook thread and the main thread. Most well-behaved loaders are unaffected.

Intl.NumberFormat v3 via V8 10.7

The new Intl.NumberFormat v3 adds formatRange() and formatRangeToParts(), trailing zero display options, and rounding modes conforming to the ECMA-402 spec update.

const fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' });
console.log(fmt.formatRange(3, 5)); // $3.00 -- $5.00