Angular reactive controls value is not updated correctly

Question

i am returning date from this function , why this function also update the StartDate controls value, for ex: if StartDate is 15Dec2019 and i want to return 17Dec2019 , and this method returning correct value but it also update the StartDate control value with returning date from the function.

this value should not be updated inside this function , here i am getting control value not updaing.this.createRecord.controls['StartDate'].value

addDays(date: Date, days: number): Date {
date.setDate(date.getDate() + days);
return date;}



GetDueDate(): Date {
#region Recurring End Type -> No Of Occurences
debugger;
const dtStart: Date = this.createRecord.controls['StartDate'].value;
let returnDate: Date;
let dtEnd: Date = dtStart;
let FrequencyId: number = +this.createRecord.controls['FrequencyId'].value;
for (let i = 1; i < +this.createRecord.controls['Occurances'].value; i++)
{
  //#region Next Date Calculation

  if (FrequencyId == 1) {
    dtEnd = this.addDays(dtStart, 1);//dtStart.(1);
  }
  else if (FrequencyId == 2) {
    dtEnd = this.addDays(dtStart, 2);
  }
  else if (FrequencyId == 3) {
    dtEnd = this.addDays(dtStart, 15);
  }
  else if (FrequencyId == 4) {
    dtEnd = this.addMonths(dtStart,4);
  }
  else if (FrequencyId == 5) {
    dtEnd = this.addMonths(dtStart, 3);
  }
  else if (FrequencyId == 6) {
    dtEnd = this.addMonths(dtStart, 6);
  }
  else if (FrequencyId == 7) {
    dtEnd = this.addYears(dtStart, 1);
  }
 //#endregion

  returnDate = dtEnd;
}

//#endregion
return returnDate;

Because you have a single Date object used for both, and muted using setDate(). Never, ever, ever call setDate(). Treat Date as an immutable class. Create a copy when you need another value. — JB Nizet
– JB Nizet, Commented Nov 30, 2019 at 14:57

Mehmet Aydoğdu · Accepted Answer · 2019-11-30 21:54:53Z

1

Date is mutable. You should create new Date.

const addDays = (date: Date, days: number): Date => {
    const newDate = new Date(date.getTime())
    newDate.setDate(newDate.getDate() + days);
    return newDate;
}
const date = new Date();
const after2Days = addDays(date, 2);
console.log('date:',date);
console.log('after2Days:',after2Days);

answered Nov 30, 2019 at 21:54

Mehmet Aydoğdu

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