how to get selected week days dates between Start date and end date with 14 day recurrence pattern using Pure JavaScript

Question

I need to return some date object which occurs between Start Date and End Date with recurrence pattern and given weekdays using pure javaScript(No postman or moment). I am able to get date object for 1 week. But I am not able to get the date object for more than a week(14 or 21 days). Here is my below code.

 function dates{
            var startDate = new Date("2020/06/22"); 
            var endDate = new Date("2020/08/16");
            var recurrencePattern = 14 ;// 2 weeks
            var daysSelected = [0,1]; //0 - sunday , 1 - monday
            var datesObj = [];
            while(startDate <= endDate){
            var i=0;
            while(i<daysSelected.length){
                if(startDate.getDay() ==  daysSelected[i]){
                   datesObj.push(startDate.getFullYear()+"-"+(startDate.getMonth()+01)+"-"+startDate.getDate());
                }
                i++;
            }
                startDate.setDate(startDate.getDate() +1);
            }
            return datesObj;
          }

the output I should get (every 2 weeks, selected Sunday and Monday fall between 22/06/2020 and 16/08/2020) is

datesObj["22-06-2020","5-07-2020","6-07-2020","19-07-2020","20-07-2020","2-08-2020","3-08-2020","16-08-2020"]

but I am getting all the Sunday and Monday dates to fall from the start and end date. Can anyone please fix this issue.

Answer 1

You can update your while(i<daysSelected.length){... } code with below code.

if (daysSelected.includes(startDate.getDay())) {
  datesObj.push(startDate.getFullYear() + "-" + (startDate.getMonth() + 01) + "-" + startDate.getDate());
}

Moreover to skip recurrencePattern = 14 days when you encounter last day of week which is startDate.getDay() == 6 then skip recurrencePattern-7+1 days. You need to subtract 7 from recurrencePattern because you are already processing for one week with loop . Also use datesObj.length > 0 so it will only skip weeks when dates are actually added for respective week.

Below is complete code. you can check it.

 function dates(startDate, endDate) { var recurrencePattern = 14; // 2 weeks var daysSelected = [0, 1]; //0 - sunday, 1 - monday var datesObj = []; while (startDate <= endDate) { if (daysSelected.includes(startDate.getDay())) { datesObj.push(startDate.getFullYear() + "-" + (startDate.getMonth() + 01) + "-" + startDate.getDate()); } if (datesObj.length > 0 && startDate.getDay() == 6) { startDate.setDate(startDate.getDate() + (recurrencePattern - 7 + 1)); } else { startDate.setDate(startDate.getDate() + 1); } } return datesObj; } console.log(dates(new Date("2020/06/22"), new Date("2020/08/16")));

Update For var daysSelected = [0, 4]; include all days between 0 to 4 .

 function dates(startDate, endDate) { var recurrencePattern = 14; // 2 weeks var daysSelected = [0, 4]; //0 - sunday to 4 - thursday var startDay = Math.min(...daysSelected); var endDay = Math.max(...daysSelected); var datesObj = []; while (startDate <= endDate) { if (startDay <= startDate.getDay() && endDay >= startDate.getDay()) { datesObj.push(startDate.getFullYear() + "-" + (startDate.getMonth() + 01) + "-" + startDate.getDate()); } if (datesObj.length > 0 && startDate.getDay() == 6) { startDate.setDate(startDate.getDate() + (recurrencePattern - 7 + 1)); } else { startDate.setDate(startDate.getDate() + 1); } } return datesObj; } console.log(dates(new Date("2020/06/22"), new Date("2020/08/16")));