Values in cells actually not formatted as well

Hello. I set values for row and set format like this:

    const row = worksheet.getRow(...);
    row.numFmt = 'hh:mm';
    row.values = userRec;

userRec is array of strings that represents time: [“10:51”,“10:56”,“10:46”] When I open created document, I see my data, formatted as I want, but: I want see sum of times, I type formula in cell =SUM(C7:D7) and see 00:00 In LibreOffice when I look in cell with tiimes I see there is symbol ’ infront of value, and when I remove it and hit enter - formula start to work. I have to do it with every cell. In MS Office I have no symbol ’ infront of value, but formula still don’t work, I have to click cell and hit enter - then formula works. That is how it looks after:

In both cases cell has right format “hh:mm” and time type. How can I fix this ?

[tvoloshyn]

The only way I managed to get durations working properly is by constructing the following date object as a value:

cell.value = new Date(
    Date.UTC(1899, 11, 30, hours, minutes, seconds, 0)
)

I believe it is something to do with how Excel stores dates (1900 / 1904 mode).

[frenzymind]

Little summary:

1. Using new Date(Date.UTC(1899, 11, 30, hours, minutes, seconds, 0)) construction really solve the issue. Thanks @tvoloshyn , but may I ask why 1899-11-30 ? I can’t found any tie to this date. Here is example:

test() {
    this.sheet.addRow([
      new Date(Date.UTC(1899, 11, 30, 16, 32, 0, 0)),
      new Date(Date.UTC(1899, 11, 30, 16, 32, 0, 0)),
    ]);

    const cellA = this.sheet.getCell('A1');
    cellA.numFmt = 'HH:MM';

    const cellB = this.sheet.getCell('B1');
    cellB.numFmt = 'HH:MM';

    const resCell = this.sheet.getCell('C1');
    resCell.value = {
      formula: 'SUM(A1:B1)',
      date1904: false,
    };
    resCell.numFmt = '[HH]:MM';

    this.book.xlsx.writeFile(`/node/app/test001.xlsx`);
  }

It gives perfect result:

• no weird single quote in front of value (libre office)
• value at once in right condition (previously I have to remove the single quote sign or clicking every cell in MS Excel)
• formula works correctly with ‘sum’ function

1. It is also possible to use strings as before, but then:

• you have strange single quote in front of value (libre office)
• ‘sum’ function is not work in cell formula
• to make cell value become natural, you have to delete single quote (in libre office) or clicking every of them in ms excel
• to calculate duration you have to use summary of all cells in formula: ‘A1+B1+C1’ and so on, as @ladaniavadh shows before

Thanks!