Cypress task with xlsx leads to f.slice when using - cypress

Question

I am getting this error when trying to access a cypress task masking the "xlsx": "^0.18.5"
for reading excel files.
From Node.js Internals:
TypeError: f.slice is not a function
at firstbyte (/local0/biologics/gitcheckouts/new-ui-e2e/node_modules/xlsx/xlsx.js:23626:38)
at readSync (/local0/biologics/gitcheckouts/new-ui-e2e/node_modules/xlsx/xlsx.js:23706:14)...
My task looks like this cypress.config.ts
on('task', {
readXlsx: readXlsx.read,
});
If I add brackets after the read:-> readXlsx: readXlsx.read() it already fails when starting cypress with the same error message:
Does anybody know what to do? (Cypress version 12.5.0)
Add on:
import * as fs from 'fs';
private validateExcelFile(countedItems: number, correction: number) {
cy.get('#LASTDOWNLOADEDFILE').then((name) => {
const fileName = name as unknown as string;
cy.log(`Validating excel file: ${fileName}`);
const buffer = fs.readFileSync(fileName);
cy.task('readXlsx', { buffer }).then((rows) => {
const rdw = (rows as string).length;
expect(rdw).to.be.equal(countedItems - correction);
});
});
}

Answer 1

I cannot tell what code, if any, precedes the task. The message seems to indicate a buffer issue, here is my working code you can compare to your own.
Otherwise, suspect the file itself.
import { readFileSync } from "fs";
import { read } from "xlsx/xlsx.mjs";
function read(name) {
const buffer = readFileSync(name);
const workbook = read(buffer);
return workbook
}
...
on('task', {
readXlsx: (name) => read(name)
...