date - Days are not added properly with momentJS in JavaScript - Stack Overflow

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I have this code where I want to get next 15 days from the start date

    var fortnightStart = moment("15 04 2015", "DD MM YYYY");

    for (var i = 1; i <= 15; i++) {

        dates.push(fortnightStart.add(i, "days").format("D MMM"));

    }

    console.log(dates);

This is the output

["16 Apr", "18 Apr", "21 Apr", "25 Apr", "30 Apr", "6 May", "13 May", "21 May", "30 May", "9 Jun", "20 Jun", "2 Jul", "15 Jul", "29 Jul", "13 Aug"]

I don't know why its missing a few days.

I have this code where I want to get next 15 days from the start date

    var fortnightStart = moment("15 04 2015", "DD MM YYYY");

    for (var i = 1; i <= 15; i++) {

        dates.push(fortnightStart.add(i, "days").format("D MMM"));

    }

    console.log(dates);

This is the output

["16 Apr", "18 Apr", "21 Apr", "25 Apr", "30 Apr", "6 May", "13 May", "21 May", "30 May", "9 Jun", "20 Jun", "2 Jul", "15 Jul", "29 Jul", "13 Aug"]

I don't know why its missing a few days.

• javascript
• date
• momentjs

Share Improve this question Follow edited Apr 23, 2015 at 3:29 Yauheni Leichanok 1,76911 gold badge2121 silver badges3030 bronze badges asked Apr 23, 2015 at 2:24 user3214546user3214546 6,8311515 gold badges5555 silver badges9898 bronze badges 1

• 2 The .add() function modifies the moment (date) object. – Pointy Commented Apr 23, 2015 at 2:36

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3 Answers 3

Sorted by: Reset to default 6

On every iteration you add i days to your initial date - so it keeps accumulating (+1, +2, +3 etc). You need to add not i but simply 1 to fortnightStart.

var fortnightStart = moment("15 04 2015", "DD MM YYYY");
for (var i = 1; i <= 15; i++) {
    // 1, not i
    dates.push(fortnightStart.add(1, "days").format("D MMM"));
}
console.log(dates);

The problem is that .add modifies the object passed in instead of creating a new date. To keep your code in its original style, you need to clone the date before adding to it.

dates.push(fortnightStart.clone().add(i, "days").format("D MMM"));

Or:

dates.push(moment(fortnightStart).add(i, "days").format("D MMM"));

The reason you're missing dates is because 'date.add' changes the current variable. E.g.

date = moment("15 04 2015", "DD MM YYYY");
date.add(1, "days");
console.log(date); // This will give you "16 04 2015"

For your code to work correctly, you need to make sure that either:

1) The 'add' method doesn't change your original value by adding to a clone. e.g.

dates.push(fortnightStart.clone().add(i, "days").format("D MMM"));

OR

2) You only add 1 day every loop instead if 'i' days. e.g.

dates.push(fortnightStart.clone().add(1, "days").format("D MMM"));

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