@ubjs/wasm

The WebAssembly player runtime for uniffi-bindgen-react-native generated bindings. Imported by generated TypeScript code; not intended for direct use.

What it does

The player reads a table of FFI signatures the bindgen emits alongside your bindings, and calls the .wasm through it. Nothing per-crate is generated in C++ or JavaScript — one runtime drives every module.

Compatibility

Runs anywhere WebAssembly does: modern browsers, Node ≥18, Bun, and web bundlers. The exports map picks the browser or node build through the browser and node conditions.

Hermes has no WebAssembly, so this does not run in a standard React Native app. Use the JSI flavor there. Metro is still supported as a web bundler (Expo Web, React Native Web).

Install

You should not install this directly. Generated bindings import it, and list @ubjs/core as a peer requirement.

npm install @ubjs/wasm @ubjs/core

Loading a module

Generated bindings export uniffiInitAsync, which takes the .wasm however your environment names it — a URL, a path, a Response, or bytes. Naming the asset is the one thing only the host knows, so there is no default.

import { uniffiInitAsync } from './generated';

import wasm from './generated/my_crate.wasm';                    // bundler
const wasm = new URL('./generated/my_crate.wasm', import.meta.url); // node

await uniffiInitAsync(wasm);

Under Metro, .wasm goes through the asset registry rather than becoming a URL; resolve it with Asset.fromModule(...).uri, or serve the file and pass its URL.

Rust side

Your crate builds a cdylib and depends on the uniffi-runtime-wasm crate, which supplies the allocator and panic hook the player calls into. ubrn build wasm2 checks both, and uniffi_core needs its wasm-unstable-single-threaded feature.