Cannot read property 'push' of undefined typescript

Question

I am trying to push a date object into an array and I get this error "cannot read property 'push' of undefined".

export class CalendarComponent { 
days: Date[]

showMonths() {

 const interval = new Interval();

    interval.fromMonth  = this.selectedFromMonth.number;
    interval.fromYear = this.selectedFromYear.number;
    interval.toMonth = this.selectedToMonth.number;
    interval.toYear = this.selectedToYear.number;

    for (let i = interval.fromMonth - 1; i < 11; i++) {
      const day = new Date(interval.fromYear, i, 1);
       this.days.push(day);
      // console.log(day);
      // days.push(day);
    }

    // console.log(day);
}

Why do I get this error if 'days' it is already an array and 'day' it is not undefined ?

You've given it a type but not a value.

jonrsharpe
– jonrsharpe

2018-07-21 08:39:10 +00:00
Commented Jul 21, 2018 at 8:39 — jonrsharpe
– jonrsharpe, Commented Jul 21, 2018 at 8:39

Suren Srapyan · Accepted Answer · 2018-07-21 08:33:57Z

8

You need to initialize your property. You have just set the type of it, but actually it is undefined.

days: Date[] = [];

answered Jul 21, 2018 at 8:33

Suren Srapyan

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Comments

Muhammed Albarmavi · Accepted Answer · 2018-07-21 08:47:42Z

1

static typing is typescript future and when you compile your code to javascript typing will gone this just a help to developer during the build time.

days: Date[] is the same you sa days and the initial value is undefined

var days;

console.log(days); // => undefined

that why you need assaign days to [] empty array before you use it

days: Date[] = [];

answered Jul 21, 2018 at 8:47

Muhammed Albarmavi

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