@marcusok/ppt-preview

Read-only .pptx preview in the browser — continuous scrolling with lazy per-slide Canvas rendering, a selectable/copyable text layer, 0-based slide navigation, and password decryption for encrypted files. Rendering is powered by a Rust/WASM parser (@silurus/ooxml 0.89.6, bundled into this package's dist — zero transitive dependencies for consumers), wrapped with format sniffing, defensive source copying and viewport-driven memory management.

Capabilities

Capability	Description
Formats	Standard OOXML .pptx. Password-protected files (OLE2/MS-OFFCRYPTO Agile encryption) decrypt when password is provided. Legacy binary .ppt is detected and reported as LEGACY_FORMAT (never silently mis-rendered)
Lazy rendering	Continuous scroll; every slide is a placeholder sized by the deck's aspect ratio (no scrollbar jumps). Slides render as they approach the viewport (1-screen preload band) and release their canvas memory when far away (beyond 3 screens)
Text layer	Text runs are collected in the same render pass (onTextRun — no double rendering); a transparent layer aligns with the canvas pixels — select and copy like real text. Off with enableTextSelection: false
Navigation	goToSlide(index) / nextSlide() / prevSlide(), 0-based, tracking the most visible slide (manual scrolling is respected). Hidden slides are all shown and counted, preserving the original deck order
Worker parsing	Parsing runs in a module Web Worker (WASM); slide layout and Canvas paint run on the main thread (mode: "main" upstream — the engine's fixed main-mode shape)
Decryption	MS-OFFCRYPTO Agile (SHA-512 key derivation + AES-CBC) via WebCrypto on the main thread — requires a secure context (HTTPS/localhost). Typically adds ~1s before parsing; ZIP-entry encryption is not covered
Hardened defaults	Sniffing runs before the engine (empty / non-ZIP / non-OLE2 inputs report early; OLE2 is passed through so the engine distinguishes legacy/encrypted/unknown CFB). Hyperlinks are inert (select/copy only); media renders as static posters (skipMediaControls)
Cancellation	destroy() disconnects observers, expires in-flight renders, zeroes canvases, removes injected DOM and destroys the engine (terminating the parser worker); all callbacks go silent. Cancellation is not an error (no onError)
Errors	Code-carrying errors: UNSUPPORTED, LEGACY_FORMAT, PASSWORD_PROTECTED, CORRUPT, UNKNOWN

Install

pnpm add @marcusok/ppt-preview

The engine (~2.5 MB JS) and its parser wasm (~2 MB, ~800 KB gzipped) ship inside this package's dist. Under Vite/webpack the wasm needs zero configuration — the bundler detects the asset next to the entry and emits it automatically. Two build-time warnings about worker assets (pptx-source-worker.mjs, assets/render-worker-*.js) are expected and safe to ignore: they belong to the engine's mode: "worker" rendering path and the legacy path, neither of which this package ever loads. See Limits.

Quick example

import { createPptPreview } from "@marcusok/ppt-preview";

const preview = createPptPreview(el, {
  source: file, // File | Blob | Uint8Array | ArrayBuffer
  slideWidth: 960, // CSS px (default); height follows the deck ratio
  password: "…", // optional; MS-OFFCRYPTO Agile files only
  onRendered: ({ slideCount, firstSlideMs, durationMs }) =>
    console.log(slideCount, firstSlideMs, durationMs),
  onError: (e) => console.error(e.code, e.message),
});

preview.nextSlide(); // 0-based navigation
preview.destroy(); // cancel in-flight work + terminate the engine

There is intentionally no low-level data-model API: the engine's slide models are tied to a live parser session and cannot be honestly detached into a plain-data parse() result. This differs from @marcusok/excel-preview, which exposes parseWorkbookBytes — see its docs for that pattern.

Not in scope (v1)

• Legacy .ppt — detected and reported as LEGACY_FORMAT; convert to .pptx upstream.
• Animations, transitions, audio/video playback — static preview only; media keeps its poster/graphics representation (no fake playback controls).
• Hyperlinks — rendered as text but inert (no click handling); opening the external-scheme allowlist and internal slide jumps is a follow-up.
• Container re-layout — slideWidth is resolved once at creation; container resizes do not re-fit (destroy + re-create instead).
• Optional engine renderers — MathJax (OMML equations), TIFF images, ChartEx, 3-D charts and Region Maps are not injected; affected content falls back to the engine's degradation (placeholder / 2-D family). See Limits.