Notices

• Threading support now requires -Clink-arg=--export=__heap_base to be set
  in RUSTFLAGS for nightly toolchains from 2026-05-06 onward, after
  rust-lang/rust#156174
  removed the implicit __heap_base/__data_end exports on wasm*
  targets. Atomics CI, CLI reference tests, and the nodejs-threads,
  raytrace-parallel, and wasm-audio-worklet examples have been
  updated to pass --export=__heap_base explicitly. The flag is
  backward-compatible with older nightlies.

• -Cpanic=unwind on wasm targets now emits modern (exnref) exception
  handling by default after
  rust-lang/rust#156061,
  and requires Node.js 22.22.3+ (for WebAssembly.JSTag). Building
  legacy EH wasm currently requires pinning to nightly-2026-05-06 or
  earlier, since user -Cllvm-args cannot override the new target spec.
  See #5151
  for tracking Node.js 20 support.

Added

• Implemented TryFromJsValue for Vec<T> where T: TryFromJsValue.
  A JS value converts when it is a real Array (per Array.isArray)
  and every element converts via T::try_from_js_value. This composes
  recursively (Vec<Vec<String>>, Vec<Option<T>>) and works for any
  T with a TryFromJsValue impl, including primitives, String,
  JsValue, and JsCast types. Array-likes (objects with length and
  numeric indices) are intentionally rejected to mirror the static ABI
  representation used by js_value_vector_from_abi.

• New extends_js_class and extends_js_namespace attributes on
  exported structs to allow defining the parent js_class name when
  it has been customized by js_name and the parent's own js_namespace
  as well in turn. New validation is added at code generation time that
  will now catch these cases instead of emitting invalid code. Example:

  #[wasm_bindgen(js_name = "Animal", js_namespace = zoo)]
  pub struct AnimalImpl { /* ... */ }
  
  #[wasm_bindgen(
      extends = AnimalImpl,
      extends_js_class = "Animal",
      extends_js_namespace = zoo,
  )]
  pub struct DogImpl { /* ... */ }

  #5154

Changed

• When an exported struct uses js_namespace, the corresponding value
  must now be repeated on every impl block. Previously the impl-side
  defaults silently worked resulting in inconsistent emission. Example:

  // Before:
  #[wasm_bindgen(js_namespace = "default")]
  pub struct Counter { /* ... */ }
  
  #[wasm_bindgen]              // worked, but fragile
  impl Counter { /* ... */ }
  
  // After:
  #[wasm_bindgen(js_namespace = "default")]
  pub struct Counter { /* ... */ }
  
  #[wasm_bindgen(js_namespace = "default")]   // now required
  impl Counter { /* ... */ }

  To ease this transition for js_namespace usage, diagnostic
  messages now include hints for missing namespaces for easier
  fixing.

  #5154

Fixed

• Fixed the descriptor interpreter panicking on Br and BrIf
  instructions emitted by recent nightly compilers when building with
  panic=unwind.
  #5158

• Emscripten output now works against vanilla upstream emscripten without
  requiring a fork. Dependency tracking, HEAP_DATA_VIEW setup,
  function-decl intrinsic inlining, catch-wrapper gating, and imported
  global handling have all been corrected; ESM imports
  (#[wasm_bindgen(module = "...")] and snippets) are emitted to a
  sidecar library_bindgen.extern-pre.js consumers pass to emcc via
  --extern-pre-js; namespaced exports (js_namespace = [...] on a
  struct/impl) now attach to Module.<segments> instead of emitting
  top-level export const (which emcc's library evaluator rejects);
  the generated .d.ts for namespaced exports is now valid TypeScript
  (mangled identifiers stay module-internal via declare class /
  declare enum / declare function plus export { BindgenModule };
  to mark the file as a module; no spurious unqualified Calc:
  property on BindgenModule for namespaced items; namespace shapes
  land as plain interface members (app: { math: { Calc: typeof app__math__Calc } };) instead of the previously-emitted export let app: { ... }; which was invalid TS1131 syntax inside an
  interface body).
  #5156

• Fixed a duplicate phantom class being emitted for an exported struct
  renamed via js_name (Rust ident != JS class name) and/or placed in a
  js_namespace, when the struct crosses the boundary as a JsValue
  (e.g. via .into()). The WrapInExportedClass / UnwrapExportedClass
  imports were keyed by the Rust ident rather than the qualified JS name
  that exported_classes is keyed by (a regression from fix: route methods to the right class when js_name + js_namespace + js_class are combined #5154), so a
  fresh empty class entry was minted and emitted alongside the real one,
  with a free() referencing a nonexistent wasm export. Riding the
  same release's fix: route methods to the right class when js_name + js_namespace + js_class are combined #5154 wire-format bump, the now-vestigial rust_name
  field is dropped from the schema and the namespace-qualified name is
  no longer cached on AuxStruct, AuxEnum, or ExportedClass
  (derived on demand from (name, js_namespace)), collapsing three
  fallback chains that only papered over the pre-fix: route methods to the right class when js_name + js_namespace + js_class are combined #5154 keying.

  #5160