Result<T, E>
T parameter | &T parameter | &mut T parameter | T return value | Option<T> parameter | Option<T> return value | JavaScript representation |
|---|---|---|---|---|---|---|
| No | No | No | Yes | No | No | Same as T, or an exception |
The Result type can be returned from functions exported to JS as well as
closures in Rust. The Ok type must be able to be converted to JS, and the
Err type must implement Into<JsValue>. Whenever Ok(val) is encountered
it's converted to JS and handed off, and whenever Err(error) is encountered
an exception is thrown in JS with error.
You can use Result to enable handling of JS exceptions with ? in Rust,
naturally propagating it upwards to the wasm boundary. Furthermore you can also
return custom types in Rust so long as they're all convertible to JsValue.
Note that if you import a JS function with Result you need
#[wasm_bindgen(catch)] to be annotated on the import (unlike exported
functions, which require no extra annotation). This may not be necessary in the
future though and it may work "as is"!.