Node.js startup snapshots

Node Congress

Node Congress 2023

Joyee Cheung

JS Nation

JSNation 2026

The JavaScript ecosystem is moving towards a standardized module system, and Node.js is evolving to aid its adoption. What actually happens when Node.js loads an ES module today? This talk walks the full pipeline - resolution, loading, parsing, compilation, linking, instantiation, and evaluation. We will cover how the work is split between V8 and Node.js, where Node.js differs from browsers and bundlers, and the recent changes in Node.js that unlocks new patterns for better interop, performance, and customization in ESM. You will leave with a clearer mental model of how ESM is loaded in Node.js, shed obsolete knowledge and misconceptions, understand where to look when your modules don't work, and learn about the new capabilities that will help you write, run, and share ESM code better on Node.js today.

Life of an ESM in Node.js – and How It's Changing for the Better

V8 provides the ability to capture a snapshot out of an initialized heap and rehydrate a heap from the snapshot instead of initializing it from scratch. One of the most important use cases of this feature is to improve the startup performance of an application built on top of V8. In this talk we are going to take a look at the integration of the V8 startup snapshots in Node.js, how the snapshots have been used to speed up the startup of Node.js core, and how user-land startup snapshots can be used to speed up the startup of user applications.