How do I create an array of incrementally higher dates?

Question

I'm trying to generate an array of times by adding 30 min repeatedly. When I do this:

let t = new Date();
    t.setHours(0, 0, 0, 0);
    t.setHours(7);
    t.setMinutes(t.getMinutes() + 30);

I get a time representing 7:30AM. However when I do this:

let t = new Date();
    t.setHours(0, 0, 0, 0);
    t.setHours(7);
    let x = [];
    while (t.getHours() <= 22) {
      t.setMinutes(t.getMinutes() + 30);
      x.push(t);
    }
    return x;

I get 30 or so items that are all 11:00PM. I'm guessing its because they are all referring to the same object instead of copying the object. Using for loop does the same thing.

How would I go about getting my desired result of an array of different times?

selbie · Accepted Answer · 2021-07-19 06:43:48Z

2

Because you are pushing the same instance of a "Date" object, t onto your array on each iteration of the loop. Each time you modify t, you are effectively modifying all the instances in your array.

You want to push a new instance of Date on each iteration of the loop. The Date class in Javascript appears to happily accept another Date instance as a constructor param, so the fix is quite easy:

Simply change this line:

x.push(t);

To this:

x.push(new Date(t));

Full solution:

let t = new Date();
t.setHours(0, 0, 0, 0);
t.setHours(7);
let x = [];
while (t.getHours() <= 22) {
  t.setMinutes(t.getMinutes() + 30);
  x.push(new Date(t));
}
return x;

answered Jul 19, 2021 at 6:43

selbie

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Janó Gáll · Accepted Answer · 2021-07-19 06:40:33Z

0

Array.from({length: 500}, (_, i) => new Date(Date.now() + i*1000*60*30))

answered Jul 19, 2021 at 6:40

Janó Gáll

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2 Comments

AsthaUndefined Over a year ago

Please add details to your answer.

Al Foиce ѫ Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

Qiimiia · Accepted Answer · 2021-07-20 09:45:01Z

0

It's beacause you are pushing the same t in your array, each time. Instead of

t.setMinutes(t.getMinutes() + 30);

use

let addedTimeInMilliSeonds = t.setMinutes(t.getMinutes() + 30);

x.push(new Date(addedTimeInMilliSeonds ));`

and you should be fine. (If you do not need t's previous values anymore)

edited Jul 20, 2021 at 9:45

answered Jul 19, 2021 at 6:50

Qiimiia

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