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WASM container id cache

Verified against code 2026-08-29.

LoroMap, LoroList, LoroText, LoroTree, LoroMovableList, and LoroCounter expose id from Rust through wasm-bindgen. The generated getter crosses into WASM and creates a new JS string on every call.

Identity and lifetime

  • HandlerTrait::id in crates/loro-internal/src/handler.rs reads the immutable BasicHandler.id for an attached handler. Detached handlers return their type-specific ID::NONE_ID placeholder.
  • Attaching does not rebind the detached JS wrapper. insertContainer returns a new attached wrapper, while the original detached handler records an attached back-reference used by getAttached().
  • Calling getAttached() on an already attached wrapper clones the Rust handler into another JS wrapper. The two wrappers have the same container id but separate wasm-bindgen pointers and cache entries.
  • wasm-bindgen sets __wbg_ptr to zero in __destroy_into_raw(). An id read after free() must keep raising wasm-bindgen's null-pointer error.

scripts/container_id_cache_patch.js therefore stores the id in a non-enumerable, module-private Symbol property on the JS wrapper. It clears the property during __destroy_into_raw() and bypasses the cache for a zero pointer. The cache has exactly the wrapper's lifetime and does not retain the wrapper from another object.

Package targets and checks

scripts/build.ts appends the cache patch to the raw wasm-bindgen module for each of nodejs, web, browser, and bundler. Normal package entrypoints and exported raw-binding subpaths therefore use the same decorated classes; post-rollup.ts derives base64 from the patched bundler target. Do not patch generated loro_wasm*.js files by hand.

Run pnpm bench-wasm-container-id from the repository root after a dev or release WASM build. The benchmark separates repeated reads of one wrapper, first reads of many wrappers, a mirror-like reused-wrapper pass, and a fresh-wrapper boundary.