Cannot create blob from result.pdf

[slashinfty]

I am attempted to compile as stated in the readme (using typescript and svelte):

import { SiglumCompiler } from '@siglum/engine';
const compiler = new SiglumCompiler({
    bundlesUrl: '/bundles',
    wasmUrl: '/busytex.wasm',
    workerUrl: '/worker.js',  // Explicit path to copied worker
});
await compiler.init();

/* inside an async function in the same file */
const result = await compiler.compile(input);
if (result.success) {
    return new Blob([result.pdf], { type: 'application/pdf' });
}

However, I receive this error:

Type 'Uint8Array | undefined' is not assignable to type 'BlobPart'.
Type 'undefined' is not assignable to type 'BlobPart'.

If I do result.pdf! to remove the possibility of undefined, I get the following error:

Type 'Uint8Array' is not assignable to type 'BlobPart'.
Type 'Uint8Array' is not assignable to type 'ArrayBufferView'.
Types of property 'buffer' are incompatible.
Type 'ArrayBufferLike' is not assignable to type 'ArrayBuffer'.
Type 'SharedArrayBuffer' is missing the following properties from type 'ArrayBuffer': resizable, resize, detached, transfer, transferToFixedLength

[adam-weber]

Hi @slashinfty thanks for the report. Two issues here:

1. pdf is undefined
result.pdf is typed as optional because it's only present when compilation succeeds. On failure, you get result.error instead. TypeScript doesn't narrow the type from just checking result.success, so you need to check pdf directly:

if (result.success && result.pdf) {

2. Uint8Array vs BlobPart

This affects any library returning Uint8Array. The problem is that TypeScript 5.x types Uint8Array.buffer as ArrayBufferLike (which includes SharedArrayBuffer), but BlobPart expects a plain ArrayBuffer. Since these types are structurally incompatible in TS's view, it rejects the assignment - even though it works perfectly fine at runtime. This isn't specific to Siglum. It affects any Uint8Array to Blob conversion in strict TS 5.x. The workaround is a type assertion:

new Blob([result.pdf as BlobPart], { type: 'application/pdf' });

Full working example:

const result = await compiler.compile(input);
if (result.success && result.pdf) {
     return new Blob([result.pdf as BlobPart], { type: 'application/pdf' });
}

If you're using SvelteKit (or any SSR framework), two additional things:

The engine requires browser APIs (indexedDB, Worker, etc.) that don't exist in Node.js, so a top-level import will crash during server-side rendering. Use a dynamic import instead so the module only loads in the browser:

// Don't do this — breaks SSR
// import { SiglumCompiler } from '@siglum/engine';

// Do this instead
const { SiglumCompiler } = await import('@siglum/engine');

If you're using Vite (which SvelteKit uses internally), add this to your vite.config.ts to prevent Vite from trying to pre-bundle the engine's WASM dependencies (which fails because esbuild can't resolve .wasm imports):

export default defineConfig({
    optimizeDeps: {
        exclude: ['@siglum/engine']
    }
});

I'll update the type definition in a future release to use Uint8Array (TS 5.7+) so the cast won't be needed.