catch - The wasm-bindgen Guide (original) (raw)

1. Introduction
2. 1. Examples
3. 1. 1.1. Hello, World!
   2. 1.2. Using console.log
   3. 1.3. Small Wasm files
   4. 1.4. Without a Bundler
   5. 1.5. Synchronous Instantiation
   6. 1.6. Importing functions from JS
   7. 1.7. Working with char
   8. 1.8. js-sys: WebAssembly in WebAssembly
   9. 1.9. web-sys: DOM hello world
   10. 1.10. web-sys: Closures
   11. 1.11. web-sys: performance.now
   12. 1.12. web-sys: using fetch
   13. 1.13. web-sys: Weather report
   14. 1.14. web-sys: canvas hello world
   15. 1.15. web-sys: canvas Julia set
   16. 1.16. web-sys: WebAudio
   17. 1.17. web-sys: WebGL
   18. 1.18. web-sys: WebSockets
   19. 1.19. web-sys: WebRTC DataChannel
   20. 1.20. web-sys: requestAnimationFrame
   21. 1.21. web-sys: A Simple Paint Program
   22. 1.22. web-sys: Wasm in Web Worker
   23. 1.23. Parallel Raytracing
   24. 1.24. Wasm Audio Worklet
   25. 1.25. web-sys: A TODO MVC App
4. 2. Reference
5. 1. 2.1. Deployment
   2. 2.2. JS snippets
   3. 2.3. Static JS Objects
   4. 2.4. Passing Rust Closures to JS
   5. 2.5. Receiving JS Closures in Rust
   6. 2.6. Promises and Futures
   7. 2.7. Iterating over JS Values
   8. 2.8. Arbitrary Data with Serde
   9. 2.9. Accessing Properties of Untyped JS Values
   10. 2.10. Working with Duck-Typed Interfaces
   11. 2.11. Command Line Interface
   12. 2.12. Optimizing for Size
   13. 2.13. Supported Rust Targets
   14. 2.14. Supported Browsers
   15. 2.15. Support for Weak References
   16. 2.16. Support for Reference Types
   17. 2.17. Supported Types
   18. 1. 2.17.1. Imported JavaScript Types
       2. 2.17.2. Exported Rust Types
       3. 2.17.3. JsValue
       4. 2.17.4. Box<[T]> and Vec
       5. 2.17.5. *const T and *mut T
       6. 2.17.6. NonNull
       7. 2.17.7. Numbers
       8. 2.17.8. bool
       9. 2.17.9. char
       10. 2.17.10. str
       11. 2.17.11. String
       12. 2.17.12. Number Slices
       13. 2.17.13. Boxed Number Slices
       14. 2.17.14. Result<T, E>
   19. 2.18. #[wasm_bindgen] Attributes
   20. 1. 2.18.1. On JavaScript Imports
       2. 1. 2.18.1.1. catch
             1. 2.18.1.2. constructor
             2. 2.18.1.3. extends
             3. 2.18.1.4. getter and setter
             4. 2.18.1.5. final
             5. 2.18.1.6. indexing_getter, indexing_setter, and indexing_deleter
             6. 2.18.1.7. js_class = "Blah"
             7. 2.18.1.8. js_name
             8. 2.18.1.9. js_namespace
             9. 2.18.1.10. method
             10. 2.18.1.11. module = "blah"
             11. 2.18.1.12. raw_module = "blah"
             12. 2.18.1.13. no_deref
             13. 2.18.1.14. static_method_of = Blah
             14. 2.18.1.15. structural
             15. 2.18.1.16. typescript_type
             16. 2.18.1.17. variadic
             17. 2.18.1.18. vendor_prefix
       3. 2.18.2. On Rust Exports
       4. 1. 2.18.2.1. constructor
             1. 2.18.2.2. js_name = Blah
             2. 2.18.2.3. js_class = Blah
             3. 2.18.2.4. readonly
             4. 2.18.2.5. skip
             5. 2.18.2.6. skip_jsdoc
             6. 2.18.2.7. start
             7. 2.18.2.8. main
             8. 2.18.2.9. typescript_custom_section
             9. 2.18.2.10. getter and setter
             10. 2.18.2.11. inspectable
             11. 2.18.2.12. skip_typescript
             12. 2.18.2.13. getter_with_clone
             13. 2.18.2.14. unchecked_return_type and unchecked_param_type
             14. 2.18.2.15. return_description and param_description
6. 3. web-sys
7. 1. 3.1. Using web-sys
   2. 3.2. Cargo Features
   3. 3.3. Function Overloads
   4. 3.4. Type Translations
   5. 3.5. Inheritance
   6. 3.6. Unstable APIs
8. 4. Testing with wasm-bindgen-test
9. 1. 4.1. Usage
   2. 4.2. Writing Asynchronous Tests
   3. 4.3. Testing in Headless Browsers
   4. 4.4. Continuous Integration
   5. 4.5. Coverage (Experimental)
10. 5. Contributing to wasm-bindgen
11. 1. 5.1. Testing
12. 5.2. Internal Design
13. 1. 5.2.1. JS Objects in Rust
       1. 5.2.2. Exporting a function to JS
       2. 5.2.3. Exporting a struct to JS
       3. 5.2.4. Importing a function from JS
       4. 5.2.5. Importing a class from JS
       5. 5.2.6. Rust Type conversions
       6. 5.2.7. Types in wasm-bindgen
14. 5.3. js-sys
15. 1. 5.3.1. Testing
       1. 5.3.2. Adding More APIs
16. 5.4. web-sys
17. 1. 5.4.1. Overview
       1. 5.4.2. Testing
       2. 5.4.3. Logging
       3. 5.4.4. Supporting More Web APIs
18. 5.5. Publishing
19. 5.6. Team

The `wasm-bindgen` Guide

catch

The catch attribute allows catching a JavaScript exception. This can be attached to any imported function or method, and the function must return aResult where the Err payload is a JsValue:

# #![allow(unused_variables)]
#fn main() {
#[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!