JavaScript: get all months between two dates?

If loading an extra library isn't a problem, you could always try the awesome MomentJS.
Gives for very clean and powerful date manipulation.

var startDate = moment('2012-04-01');
var endDate = moment('2014-11-01');

var dates = [];
endDate.subtract(1, "month"); //Substract one month to exclude endDate itself

var month = moment(startDate); //clone the startDate
while( month < endDate ) {
    month.add(1, "month");
    dates.push(month.format('YYYY-MM-DD'));
}

console.log(dates);

JSFiddle here

const getMonths = (fromDate, toDate) => {
    const fromYear = fromDate.getFullYear();
    const fromMonth = fromDate.getMonth();
    const toYear = toDate.getFullYear();
    const toMonth = toDate.getMonth();
    const months = [];

    for(let year = fromYear; year <= toYear; year++) {
        let monthNum = year === fromYear ? fromMonth : 0;
        const monthLimit = year === toYear ? toMonth : 11;

        for(; monthNum <= monthLimit; monthNum++) {
            let month = monthNum + 1;
            months.push({ year, month });
        }
    }
    return months;
}

const sample = getMonths(new Date('2022-07-28'), new Date('2023-03-20'));
console.log(sample);
document.write('check the console output');

https://jsfiddle.net/xfayoqvs/

You can also use the excellent moment.js library:

var startDate = moment('2012-04-01');
var endDate = moment('2014-11-01');

var result = [];

if (endDate.isBefore(startDate)) {
    throw "End date must be greated than start date."
}      

while (startDate.isBefore(endDate)) {
    result.push(startDate.format("YYYY-MM-01"));
    startDate.add(1, 'month');
}

JSFiddle

This should produce the desired output:

function dateRange(startDate, endDate) {
  var start      = startDate.split('-');
  var end        = endDate.split('-');
  var startYear  = parseInt(start[0]);
  var endYear    = parseInt(end[0]);
  var dates      = [];

  for(var i = startYear; i <= endYear; i++) {
    var endMonth = i != endYear ? 11 : parseInt(end[1]) - 1;
    var startMon = i === startYear ? parseInt(start[1])-1 : 0;
    for(var j = startMon; j <= endMonth; j = j > 12 ? j % 12 || 11 : j+1) {
      var month = j+1;
      var displayMonth = month < 10 ? '0'+month : month;
      dates.push([i, displayMonth, '01'].join('-'));
    }
  }
  return dates;
}

Just call it with your existing date format:

dateRange('2013-11-01', '2014-06-01')
// ["2013-11-01", "2013-12-01", "2014-01-01", "2014-02-01", "2014-03-01", "2014-04-01", "2014-05-01", "2014-06-01", "2014-07-01", "2014-08-01", "2014-09-01", "2014-10-01", "2014-11-01", "2014-12-01"]