I want to display the days of the week based on the days in a month. Now it is the case that Sunday is always counted twice. However, when I open the debugger and set a breakpoint in the for loop, the "0" for Sunday is only counted once. How so ?

function getDayName(dateStr, locale) {
var date = new Date(dateStr);
return date.toLocaleDateString(locale, { weekday: "long" });
}

const Items = () => {
let array = [];
const d = new Date();
let tageImMonat = daysInMonth(d.getMonth() + 1, d.getFullYear());

for (var i = 1; i <= tageImMonat; i++) {
var newDate = new Date(d.getFullYear(), d.getMonth(), i);
var day = getDayName(newDate, "de-DE");
if (newDate.getDay() === 0) {
  //if Sunday
  array.push(
    <Item sx={{ backgroundColor: "red", textAlign: "left" }}>
      {i} {day}
    </Item>
  );
}
if (newDate.getDay() === 6) {
  //if Saturday
  array.push(
    <Item sx={{ backgroundColor: "lightgrey", textAlign: "left" }}>
      {i} {day}
    </Item>
  );
} else if (newDate.getDay() !== 0 || newDate.getDay() !== 6) {
  array.push(
    <Item sx={{ textAlign: "left" }}>
      {i} {day}
    </Item>
   );
  }
}

  return array;
};