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52 lines
2.3 KiB
Markdown
52 lines
2.3 KiB
Markdown
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# `js-sys`
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The [`js-sys` crate][js-sys] provides raw bindings to all the global APIs
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guaranteed to exist in every JavaScript environment by the ECMAScript standard,
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and its source lives at [`wasm-bindgen/crates/js-sys`][src]. With the `js-sys`
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crate, we can work with `Object`s, `Array`s, `Function`s, `Map`s, `Set`s,
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etc... without writing the `#[wasm_bindgen]` imports by hand.
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Documentation for this crate will eventually be available on [docs.rs][docsrs]
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but temporarily you can also check out the [master branch
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documentation][masterdoc] for the crate.
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[docsrs]: https://docs.rs/js-sys
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[masterdoc]: https://rustwasm.github.io/wasm-bindgen/api/js_sys/
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[src]: https://github.com/rustwasm/wasm-bindgen/tree/master/crates/js-sys
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For example, we can invoke JavaScript [`Function`][mdn-function] callbacks and
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time how long they take to execute with [`Date.now()`][mdn-date-now], and we
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don't need to write any JS imports ourselves:
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```rust
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extern crate js_sys;
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extern crate wasm_bindgen;
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use wasm_bindgen::prelude::*;
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#[wasm_bindgen]
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pub fn timed(callback: &js_sys::Function) -> f64 {
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let then = js_sys::Date::now();
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callback.apply(JsValue::null(), &js_sys::Array::new()).unwrap();
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let now = js_sys::Date::now();
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now - then
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}
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```
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The `js-sys` crate isn't quite 100% feature complete yet. There are still some
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JavaScript types and methods that we don't have bindings for. If you'd like to
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help out check out [the contribution documentation][contrib].
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Also, as mentioned above, the `js-sys` crate doesn't contain bindings to any Web
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APIs like [`document.querySelectorAll`][mdn-qsa]. These will be part of the
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[`web-sys`](./web-sys.html) crate.
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[MDN]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects
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[js-sys]: https://crates.io/crates/js-sys
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[issue]: https://github.com/rustwasm/wasm-bindgen/issues/275
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[mdn-function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
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[mdn-qsa]: https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelectorAll
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[web-sys-contributing]: https://rustwasm.github.io/wasm-bindgen/web-sys.html
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[web-sys-issues]: https://github.com/rustwasm/wasm-bindgen/issues?q=is%3Aissue+is%3Aopen+label%3Aweb-sys
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[mdn-date-now]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/now
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[contrib]: https://github.com/rustwasm/wasm-bindgen/issues/275
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