角度反应控制值未正确更新

Question

我从这个函数返回日期，为什么这个函数也更新 StartDate 控件值，例如：如果 StartDate 是 15Dec2019 并且我想返回 17Dec2019 ，并且这个方法返回正确的值，但它也更新了 StartDate 控件值与返回日期从功能。

这个值不应该在这个函数内更新，在这里我得到的控制值没有更新。 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;

Answer 1

日期是可变的。 您应该创建新的日期。

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);