Excel in Node.js

import { readFile, writeFile } from "node:fs/promises";
import { fromXlsxWorkbook, toXlsxWorkbook, type XlsxWorkbookOptions } from "@sheetwrite/core";
import "@sheetwrite/xlsx/register";

declare const source: string;
declare const destination: string;
declare const options: XlsxWorkbookOptions;

const snapshot = await fromXlsxWorkbook(await readFile(source), options);
await writeFile(destination, await toXlsxWorkbook(snapshot, options), { flag: "wx" });

For this input the command prints Saved 1 sheet(s) to output.xlsx. This is a workbook conversion, not an image or a browser download.

Try it live → Browser spreadsheet showcase

The live showcase is a browser counterpart. Run the command below for the Node file-system path.

$ npm install @sheetwrite/core @sheetwrite/xlsx
npm install --save-dev tsx @types/node

import { readFile, writeFile, stat } from "node:fs/promises";
import {
  fromXlsxWorkbook, toXlsxWorkbook, isSheetwriteError,
  type XlsxWorkbookOptions,
} from "@sheetwrite/core";
import "@sheetwrite/xlsx/register";

const [source, destination] = process.argv.slice(2);
if (!source || !destination) throw new Error("Usage: roundtrip.mts input.xlsx output.xlsx");
if (source === destination) throw new Error("Choose a separate output path");
const controller = new AbortController();
const cancel = () => controller.abort();
process.once("SIGINT", cancel);
const options: XlsxWorkbookOptions = {
  signal: controller.signal,
  maxCells: 100_000,
  resourceLimits: { maxInputBytes: 8 * 1024 * 1024 },
  onWarning: (warning) => console.warn(`${warning.code}: ${warning.message}`),
};
try {
  if ((await stat(source)).size > 8 * 1024 * 1024) throw new Error("Input exceeds 8 MiB");
  const snapshot = await fromXlsxWorkbook(await readFile(source), options);
  const output = await toXlsxWorkbook(snapshot, options);
  if (controller.signal.aborted) throw new Error("Cancelled");
  await writeFile(destination, output, { flag: "wx" });
  console.log(`Saved ${snapshot.sheets.length} sheet(s) to ${destination}`);
} catch (error) {
  console.error(isSheetwriteError(error) ? `${error.code}: ${error.message}` : error);
  process.exitCode = 1;
} finally {
  process.removeListener("SIGINT", cancel);
}

npx tsx roundtrip.mts input.xlsx output.xlsx

Server ownership and errors

These workbook codec functions operate on a WorkbookSnapshot. They do not create a Grid, initialize a formula engine, evaluate formulas, access the DOM or call downloadBytes. Formula source is preserved where supported, not recalculated by this script. Node's Buffer is a Uint8Array, so readFile bytes can go directly to fromXlsxWorkbook.

The script never substitutes a mock workbook. Missing or invalid files fail. flag: "wx" refuses to overwrite an existing output; use a separate output path. File helpers close their own file handles. The finally block removes the process listener, and SIGINT requests codec cancellation between bounded stages. It does not interrupt writeFile once that write has started.

Options and resource limits

The stat check is not a security boundary for a file another process can modify. The codec also checks the bytes it actually receives. ZIP expansion, entry count, compression ratio and XML depth retain their default limits. XlsxResourceError also satisfies isSheetwriteError; report its stable code and resource details rather than parsing a message.

Buffered import holds input bytes and the resulting snapshot; buffered export also holds output bytes. Streaming workbook export can bound output chunks, but it does not make the snapshot disappear. Do not promise constant-memory processing for large workbooks. See streaming and kept-part rules before using this as a fidelity-sensitive round trip. An unchanged chart or pivot graph can be kept; that is not a chart-authoring or pivot-calculation API.