2aac606d3f
Support was previously (re-)added in #1654 for importing direct JS values into a WebAssembly module by completely skipping JS shim generation. This commit takes that PR one step further by *also* embedding a direct import in the wasm file, where supported. The wasm file currently largely just imports from the JS shim file that we generate, but this allows it to directly improt from ES modules where supported and where possible. Note that like #1654 this only happens when the function signature doesn't actually require any conversions to happen in JS (such as handling closures). For imports from ES modules, local snippets, or inline JS they'll all have their import directives directly embedded into the final WebAssembly binary without any shims necessary to hook it all up. For imports from the global namespace or possibly vendor-prefixed items these still unconditionally require an import shim to be generated because there's no way to describe that import in an ES-friendly way (yet). There's a few consequences of this commit which are also worth noting: * The logic in `wasm-bindgen` where it gracefully handles (to some degree) not-defined items now only is guaranteed to be applied to the global namespace. If you import from a module, it'll be an instantiation time error rather than today's runtime error when the import is called. * Handling imports in the wasm module not registered with `#[wasm_bindgen]` has become more strict. Previously these imports were basically ignored, leaving them up for interpretation depending on the output format. The changes for each output target are: * `bundler` - not much has changed here. Previously these ignored imports would have been treated as ES module imports, and after this commit there might just be some more of these imports for bundlers to resolve. * `web` - previously the ignored imports would likely cause instantiation failures because the import object never actually included a binding for other imports. After this commit though the JS glue which instantiates the module now interprets all unrecognized wasm module imports as ES module imports, emitting an `import` directive. This matches what we want for the direct import functionality, and is also largely what we want for modules in general. * `nodejs` - previously ignored imports were handled in the translation shim for Node to generate `require` statements, so they were actually "correctly handled" sort of with module imports. The handling of this hasn't changed, and reflects what we want for direct imports of values where loading a wasm module in Node ends up translating the module field of each import to a `require`. * `no-modules` - this is very similar to the `web` target where previously this didn't really work one way or the other because we'd never fill in more fields of the import object when instantiating the module. After this PR though this is a hard-error to have unrecognized imports from `#[wasm_bindgen]` with the `no-modules` output type, because we don't know how to handle the imports. Note that this touches on #1584 and will likely break the current use case being mentioned there. I think though that this tightening up of how we handle imports is what we'll want in the long run where everything is interpreted as modules, and we'll need to figure out best how wasi fits into this. This commit is unlikely to have any real major immediate effects. The goal here is to continue to inch us towards a world where there's less and less JS glue necessary and `wasm-bindgen` is just a polyfill for web standards that otherwise all already exist. Also note that there's no explicitly added tests for this since this is largely just a refactoring of an internal implementation detail of `wasm-bindgen`, but the main `wasm` test suite has many instances of this path being taken, for example having imports like: (import "tests/wasm/duplicates_a.js" "foo" (func $__wbg_foo_969c253238f136f0 (type 1))) (import "tests/wasm/duplicates_b.js" "foo" (func $__wbg_foo_027958cb2e320a94 (type 0))) (import "./snippets/wasm-bindgen-3dff2bc911f0a20c/inline0.js" "trivial" (func $__wbg_trivial_75e27c84882af23b (type 1))) (import "./snippets/wasm-bindgen-3dff2bc911f0a20c/inline0.js" "incoming_bool" (func $__wbg_incomingbool_0f2d9f55f73a256f (type 0)))
wasm-bindgen
Facilitating high-level interactions between Wasm modules and JavaScript.
Guide | API Docs | Contributing | Chat
Built with 🦀🕸 by The Rust and WebAssembly Working Group
Example
Import JavaScript things into Rust and export Rust things to JavaScript.
use wasm_bindgen::prelude::*;
// Import the `window.alert` function from the Web.
#[wasm_bindgen]
extern "C" {
fn alert(s: &str);
}
// Export a `greet` function from Rust to JavaScript, that alerts a
// hello message.
#[wasm_bindgen]
pub fn greet(name: &str) {
alert(&format!("Hello, {}!", name));
}
Use exported Rust things from JavaScript with ECMAScript modules!
import { greet } from "./hello_world";
greet("World!");
Features
-
Lightweight. Only pay for what you use.
wasm-bindgenonly generates bindings and glue for the JavaScript imports you actually use and Rust functionality that you export. For example, importing and using thedocument.querySelectormethod doesn't causeNode.prototype.appendChildorwindow.alertto be included in the bindings as well. -
ECMAScript modules. Just import WebAssembly modules the same way you would import JavaScript modules. Future compatible with WebAssembly modules and ECMAScript modules integration.
-
Designed with the "Web IDL bindings" proposal in mind. Eventually, there won't be any JavaScript shims between Rust-generated wasm functions and native DOM methods. Because the wasm functions are statically type checked, some of those native methods' dynamic type checks should become unnecessary, promising to unlock even-faster-than-JavaScript DOM access.
Guide
📚 Read the wasm-bindgen guide here! 📚
You can find general documentation about using Rust and WebAssembly together here.
API Docs
License
This project is licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
See the "Contributing" section of the guide for information on
hacking on wasm-bindgen!
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this project by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.