dateNF seems to be ignored

Hey there,

First of all, I’ve prepared a minimal demo of the issue I’m running into. You can find it here: https://github.com/pkaske/xlsx-date-issue

You should just need to clone, npm install and node ./index.js it to reproduce.

Input data
input.xlsx contains the following data:

The date format you see here is German (DD.MM.YYYY).
The cells are formated as dates in excel (2010).

What I want to accomplish
I want to convert that table to CSV and keep the date format as it is displayed in the screenshot (DD.MM.YYY).

This is what I tried

const stream = XLSX.stream.to_csv(worksheet, {
  FS: ';',
  RS: '\n',
  dateNF: 'dd.mm.yyyy',   // <--- Seems to be ignored.
  strip: false,
  blankrows: true
});

stream.pipe(Fs.createWriteStream(output))
  .on('finish', () => {
    console.log(output, 'written');
  });

The actual output is

Name;Date
Person 1;12/31/18
Person 2;2/13/18
Person 3;4/5/18

Expected output
The dates should read 31.12.2018, 13.02.2018 and 05.04.2018.

Hopefully I just did something silly and that’s all 😃

[kalinchernev]

@sonjadeissenboeck regarding https://github.com/SheetJS/js-xlsx/issues/718#issuecomment-430628199, having same situation.

For me, it helped to work with the formatting in the data reading:

const workbook = XLSX.read(data, {
  cellDates: true,
  dateNF: 'dd/mm/yyyy',
});

And you leave the XLSX.utils.sheet_to_json({ raw: false })

[SheetJSDev]

Both of us did something silly 😃

tl;dr:

const workbook = XLSX.readFile(input, {cellText:false, cellDates:true});
// ...
const stream = XLSX.stream.to_csv(worksheet, {
  FS: ';',
  RS: '\n',
  dateNF: 'dd"."mm"."yyyy', // <-- notice the double quotes
  strip: false,
  blankrows: true
});

How does Excel handle international dates?

Excel dates are somewhat hokey. In the file, if you unzip and take a peek at xl/worksheets/sheet1.xml you’ll see entries like

      <c r="B2" s="1">
        <v>43465</v>
      </c>

The reader has to figure out that the number corresponds to a date and convert it back. To do that it looks at the cell format from xl/styles.xml:

    <xf numFmtId="14" fontId="0" fillId="0" borderId="0" xfId="0" applyNumberFormat="1" applyFill="1"/>

All it stores is the number 14. Based in new york, your file looks like:

By fiddling with the regional settings, the same exact file will be displayed differently. https://github.com/SheetJS/js-xlsx/issues/326#issuecomment-286014758 is one comment showing a few different regional setting screenshots against Excel 95

What you should do

To override the date format, you must force the reader to ignore the original number format and force the writer to use a valid cell format.

On the read side, the line should be:

const workbook = XLSX.readFile(input, {cellText:false, cellDates:true});

the cellText:false option skips generation of the original strings (the w field is omitted) and cellDates:true forces generation of date objects for cells that are possibly dates (instead of the file’s number values). After doing this, the worksheet date cells look like:

{
// ...
  B2: { t: 'd', v: 2018-12-31T00:00:00.000Z },
//...
}

On the write side, you need to quote the periods:

const stream = XLSX.stream.to_csv(worksheet, {
  FS: ';',
  RS: '\n',
  dateNF: 'dd"."mm"."yyyy',
  strip: false,
  blankrows: true
});

Why are quotes required in the date format?

The format displayed in the UI is not necessarily the same as the format displayed in the file. I took your file and changed one of the cells to follow the dd.mm.yyyy format in the UI. When saving the file, the actual format entry looks like:

    <numFmt numFmtId="165" formatCode="dd\.mm\.yyyy"/>

Excel is automagically fixing the decimal points as literal. The double quotes achieve the same effect.

What we should be doing

1. The library should really take a locale option that sets everything up automatically. The ideal resolution is:

const workbook = XLSX.readFile(input, {locale:"en-US"});

1. Common format errors should be autocorrected in the same way that Excel corrects them.