incrementmonth.js

// This modified snippet is from a function that accepts the current month(currentmonth) and period(period) and adds the period to the current month and lists every month within the new period. It can accept negative or positive periods.

function iterveningMonths(year, month, period) {
    var movement = period < 0 ? -1 : 1; //Which way are we going?
    var out = [];
    var result;
    
    for (var i = Math.abs(period); i !== 0; i--) {
        month += movement; //Increment or decrement month
        result = month % 12; //Check to see where that month is on a 12 month[0..11] period
        year = result === 0 ? year+movement : year; //Track the year while we're at it
        out.push(result < 0 ? year + "-" + (result + 12) : year + "-" + result); //Push result to end of array
    }
    return out;
}

console.log(iterveningMonths(2012, 3, -50));

function iterveningMonths(start, end){
var movement = start > end ? -1 : 1;
var out = [];
for (var current = start; current !== end; current += movement) {
out.push(current % 12);
}
return out;
}

console.log(iterveningMonths(1, 20))

Love it, thanks!

Actually, @Benvie, it didn't work very well as it didn't handle negative periods very well nor did it loop properly.
If you apply a negative period, say -3 to a starting month being 1. You should get [0,11,12[ and not [1,0,1]

I still used some of the principles in your code snippet though. Thanks.