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Maintaining WebAssembly

Support for WebAssembly has been identified as one of the top technical priorities for the future success of Node.js.

This document provides an overview of our high-level strategy for supporting WebAssembly and information about our current implementation as a starting point for contributors.

High-level approach​

The key elements of our WebAssembly strategy include:

  • Up-to-date core WebAssembly support
  • Support for high-level APIs
  • Making it easy to load WebAssembly
  • Making sure the core Node.js APIs are compatible with WebAssembly and can be called in an efficient manner from WebAssembly

Up-to-date core WebAssembly support​

Node.js gets its core WebAssembly support through V8. We don't need to do anything specific to support this, all we have to do is keep the version of V8 as up-to-date as possible.

Key API support​

As a runtime, Node.js must implement a number of APIs in addition to the core WebAssembly support in order to be a good choice to run WebAssembly. The project has currently identified these additional APIs as important:

  • WebAssembly System Interface (WASI). This provides the ability for WebAssembly to interact with the outside world. Node.js currently has an implementation (see below for more details).
  • WebAssembly Web API. Node.js currently has an implementation of streaming module compilation and instantiation. As this and other specifications evolve, keeping up with them will be important.
  • WebAssembly Component Model. This API is still in the definition stage but the project should keep track of its development as a way to simplify native code integration.

Making it as easy as possible to load WASM​

The most important thing we can do on this front is to either find and reference resources or provide resources on how to:

  • Compile your WebAssembly code (outside of Node.js) and integrate that into an npm workflow.
  • Load and run WebAssembly code in your Node.js application.

It is also important to support and track the ongoing work in ESM to enable loading of WebAssembly with ESM.

Making sure the core Node.js APIs are compatible with WebAssembly​

Use cases for which Node.js will be a good runtime will include code both in JavaScript and compiled into WebAssembly. It is important that Node.js APIs are able to be called from WebAssembly in an efficient manner without extra buffer copies. We need to:

  • Review APIs and identify those that can be called often from WebAssembly.
  • Where appropriate, make additions to identified APIs to allow a pre-existing buffer to be passed in order to avoid copies.

Current implementation and assets​

WebAssembly System Interface (WASI)​

The Node.js WASI implementation is maintained in the uvwasi repository in the Node.js GitHub organization. As needed, an updated copy is vendored into the Node.js deps in deps/uvwasi.

In addition to the code from uvwasi, Node.js includes bindings and APIs that allow WebAssembly to be run with WASI support from Node.js. The documentation for this API is in WebAssembly System Interface (WASI).

The implementation of the bindings and the public API is in: