Differences And Restrictions

WebAssembly intentionally excludes Node/V8 facilities. Public APIs do not accept filesystem paths, Node streams, Node callbacks, InputFile, OutputFile, plugin loaders, or synchronous CommonJS loading. Emscripten filesystem support, where used internally, is not a public storage API.

OpenSSL is excluded, but bundled RC4 and AES-128 support byte-first recrypt and Recipe encrypt(). PDF 2.0/AES-256 encryption remains unavailable. Existing byte-backed PDFs can be read, modified, and copied, but persistent-file continuation, password-protected Recipe source editing, and the path-based Recipe constructor are unavailable. Wasm recryptAsync() returns a promise like native's. Native recrypts on a libuv pool thread; Wasm has no thread pool, so it recrypts in a worker it starts itself: worker_threads in Node, Deno, and Bun, and a module Worker in browsers. Inside a worker, where no worker can start, with module options a worker cannot receive, or with the Wasm-only module option recryptWorker: false, it recrypts on the calling thread, as fast and as blocking as recrypt(). It also rejects for an unsupported source or option, where native recryptAsync() throws synchronously for wrong arguments, as every Wasm *Async method rejects. See Change PDF Passwords.

Recipe.thirdPartyLicenses() is Wasm-only: it reads the third-party notices embedded in a .wasm (see License Notices). The native packages ship their notices as THIRD_PARTY_NOTICES.md and have no such function.

Recipe bundles Roboto Regular as its default rather than native Recipe's Helvetica family. Bold and italic fall back to regular unless their byte fonts are registered, and the different metrics can change wrapping. The low-level writer does not load the bundled font.

Table header styling follows native precedence and is independent of body text styles. See Create Multi-Page Tables for header overrides; font metrics remain the source of typography differences.

Wasm Recipe does not support native chroma("!load", path) color-file loading. Register named colors individually, including Separation colors.

The Recipe HTML subset is DOM-free and Worker-safe. It supports URL links through <a href> and visual nested lists through ul, ol, and li, but does not provide arbitrary DOM, general CSS inheritance, semantic tagged-PDF lists, or plugin HTML handlers. It is also more forgiving than the XML-strict native parser: an omitted </li> ends that item at its next sibling or at the end of its list rather than throwing. Wasm htmlToTextObjects() returns flat visual runs with list prefixes and indent values, while native returns its nested XML-derived layout tree.

In a flowed text(), highlight, underline, strikeOut, and squiggly annotate the run that sets them, as links do on both ends. Native Recipe currently takes them from the call that ends the flow and spans each over the whole line (#909). Its textBox.textAlign aligns the whole flow as the call that ends it sets it, merged over the earlier runs' options. Native Recipe places each run by that run's own alignment, so runs of one line that set different alignments overlap or leave a gap.

Appending or rebuilding an existing source page does not deep-copy that page's /Annots graph, although annotations created in the output are written normally. split() returns named byte arrays rather than writing an output directory, and structure("json") returns an in-memory summary rather than writing a diagnostic file.

Wasm-only Recipe.dispose() and Recipe.disposeAssets() release Emscripten allocations that JavaScript garbage collection cannot reclaim. Native objects use normal native lifetime management. See the Recipe topic guides for examples that follow these boundaries.