Fabio B. Fabio B. - 4 months ago 8
Javascript Question

Moment JS start and end of given month

I need to calculate a JS date given year=2014 and month=9 (September 2014).

I tried this:

var moment = require('moment');
var startDate = moment( year+'-'+month+'-'+01 + ' 00:00:00' );
var endDate = startDate.endOf('month');
console.log(startDate.toDate());
console.log(endDate.toDate());


Both of logs show:

Tue Sep 30 2014 23:59:59 GMT+0200 (CEST)
Tue Sep 30 2014 23:59:59 GMT+0200 (CEST)


End date is correct but... why the start date is not?

Answer

That's because endOf mutates the original value.

Relevant quote:

Mutates the original moment by setting it to the end of a unit of time.

Here's an example function that gives you the output you want:

function getMonthDateRange(year, month) {
    var moment = require('moment');

    // month in moment is 0 based, so 9 is actually october, subtract 1 to compensate
    // array is 'year', 'month', 'day', etc
    var startDate = moment([year, month]).add(-1,"month");

    // Clone the value before .endOf()
    var endDate = moment(startDate).endOf('month');

    // just for demonstration:
    console.log(startDate.toDate());
    console.log(endDate.toDate());

    // make sure to call toDate() for plain JavaScript date type
    return { start: startDate, end: endDate };
}

References: