vellora

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Concurrency ​

vellora renders in-process through a native addon — there is no subprocess and no headless browser to pool. renderPdf returns a Promise<Uint8Array>, so rendering many documents is ordinary async JavaScript.

Render many documents ​

Render concurrently with Promise.all:

js
import { renderPdf } from "vellora";

const invoices = [/* ...data objects... */];

const pdfs = await Promise.all(
  invoices.map((data) => renderPdf(template, data)),
);

Each call is independent and produces its own Uint8Array.

Bounding concurrency ​

Unbounded Promise.all over a very large batch will start every render at once. For large batches, use renderPdfBatch to cap the number of active renders while preserving the input order:

js
import { renderPdfBatch } from "vellora";

const pdfs = await renderPdfBatch(
  invoices.map((data) => ({ html: template, data })),
  { concurrency: 8 },
);

If concurrency is omitted, vellora uses 4. The value must be a positive safe integer.

Determinism under concurrency ​

Rendering is deterministic: the same (html, data, opts) always yields byte-identical output regardless of how many renders run alongside it. Concurrent calls do not share mutable state that would change each other's results.