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# `catch`
The `catch` attribute allows catching a JavaScript exception. This can be
attached to any imported function or method, and the function must return a
`Result` where the `Err` payload is a `JsValue`:
```rust
#[wasm_bindgen]
extern "C" {
// `catch` on a standalone function.
#[wasm_bindgen(catch)]
fn foo() -> Result<(), JsValue>;
// `catch` on a method.
type Zoidberg;
#[wasm_bindgen(catch, method)]
fn woop_woop_woop(this: &Zoidberg) -> Result<u32, JsValue>;
}
```
If calling the imported function throws an exception, then `Err` will be
returned with the exception that was raised. Otherwise, `Ok` is returned with
the result of the function.
> By default `wasm-bindgen` will take no action when wasm calls a JS function
> which ends up throwing an exception. The wasm spec right now doesn't support
> stack unwinding and as a result Rust code **will not execute destructors**.
> This can unfortunately cause memory leaks in Rust right now, but as soon as
> wasm implements catching exceptions we'll be sure to add support as well!
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30 entries across 30 versions & 1 rubygems