Unstable APIs - The wasm-bindgen Guide (original) (raw)

  1. Introduction
  2. 1. Examples
    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
    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
      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
      1. 2.18.1. On JavaScript Imports
        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
        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
    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
    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
    1. 5.1. Testing
  12. 5.2. Internal Design
    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
    1. 5.3.1. Testing
      1. 5.3.2. Adding More APIs
  16. 5.4. web-sys
    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

Unstable APIs

It's common for browsers to implement parts of a web API while the specification for that API is still being written. The API may require frequent changes as the specification continues to be developed, so the WebIDL is relatively unstable.

This causes some challenges for web-sys because it means web-sys would have to make breaking API changes whenever the WebIDL changes. It also means that previously published web-sys versions would be invalid, because the browser API may have been changed to match the updated WebIDL.

To avoid frequent breaking changes for unstable APIs, web-sys hides all unstable APIs through an attribute that looks like:


# #![allow(unused_variables)]
#fn main() {
#[cfg(web_sys_unstable_apis)]
pub struct Foo;
#}

By hiding unstable APIs through an attribute, it's necessary for crates to explicitly opt-in to these reduced stability guarantees in order to use these APIs. Specifically, these APIs do not follow semver and may break whenever the WebIDL changes.

Crates can opt-in to unstable APIs at compile-time by passing the cfg flagweb_sys_unstable_apis.

Typically the RUSTFLAGS environment variable is used to do this. For example:

RUSTFLAGS=--cfg=web_sys_unstable_apis cargo run

Alternatively, you can create a cargo config fileto set its rustflags:

Within ./.cargo/config.toml:

[build]
rustflags = ["--cfg=web_sys_unstable_apis"]