Javascript TypeError: startDate.getDate is not a function-CodePudding

I have the following date variable, which outputs like this:

2021-09-06T00:00:00.000Z

I am trying to check if this date is a monday, if it is, then get the friday date (of that week). if it isn't then get the following weeks monday and friday dates. This is the code i have so far:

      startDate = new Date(startDate);

      let dayNumber = startDate.getDay();

      //if start date is a monday
      if (dayNumber == 1) {
        //set the end date as the friday
        endDate = startDate.setDate(startDate.getDate()   5);
      }

      //if the start date isn't a monday
      else {
        let daysTilMonday = 7 - dayNumber;
        //find the next monday
        startDate = startDate.setDate(startDate.getDate()   daysTilMonday);
        //set the end date as the friday
        endDate = startDate.setDate(startDate.getDate()   5);
      }

However i'm getting this error:

TypeError: startDate.getDate is not a function

CodePudding user response：

Date#setDate set date for itself and return long value of that date

startDate = startDate.setDate(startDate.getDate()   daysTilMonday);
//set the end date as the friday
endDate = startDate.setDate(startDate.getDate()   5);

Just don't assign your startDate and endDate:

startDate = '2021-09-06T00:00:00.000Z'

startDate = new Date(startDate);

let dayNumber = startDate.getDay();
let endDate;

//if start date is a monday
if (dayNumber == 1) {
    //create and set the end date as the friday
    endDate = new Date(startDate);
    endDate.setDate(endDate.getDate()   5);
}
//if the start date isn't a monday
else {
    let daysTilMonday = 7 - dayNumber;
    //find the next monday
    startDate.setDate(startDate.getDate()   daysTilMonday);
    //create and set the end date as the friday
    endDate = new Date(startDate);
    endDate.setDate(endDate.getDate()   5);
}

console.log(startDate);
console.log(endDate);