Get month if we know only Week number and year + include workdays

month.gs

var DAY_MILLIS = 24 * 60 * 60 * 1000;

function main(data_start, data_end) {



    //var ss = SpreadsheetApp.openById("Table_ID");
    //var name = ss.getName();  
    //var sheet = ss.getSheetByName('Sheet1'); // or whatever is the name of the sheet 

    //var start = sheet.getRange(2,4); 
    //var data_start = start.getValue();
    //var end = sheet.getRange(2,5); 
    //var data_end = end.getValue();

    var a = data_start;
    var b = data_end;
    var dates = createDateSpan(a, b);

    var d = new Date();

    var startDate = data_start;
    var endDate = data_end;
    var n = d.getDay();
    var tempDate;
    var arr1 = [];
    for (tempDate = startDate; tempDate < endDate; tempDate.setDate(tempDate.getDate() + 1)) {
        if (tempDate.getDay() == 1 || tempDate.getDay() == 2 || tempDate.getDay() == 3 || tempDate.getDay() == 4 || tempDate.getDay() == 5) {
            arr1.push(tempDate.getMonth() + 1);
            var massss = arr1
            //Logger.log(arr1);
        }
    }
    var final = searchMostCommonNumber(massss);
    Logger.log(final);
    //SpreadsheetApp.getActiveSheet().getRange('A2').setValue(final);
    return final;
}



function createDateSpan(startDate, endDate) {
    if (startDate.getTime() > endDate.getTime()) {
        throw Error('Start is later than end');
    }

    var dates = [];

    var curDate = new Date(startDate.getTime());
    while (!dateCompare(curDate, endDate)) {
        dates.push(curDate);
        curDate = new Date(curDate.getTime() + DAY_MILLIS);
    }
    dates.push(endDate);
    return dates;

}




function dateCompare(a, b) {
    return a.getFullYear() === b.getFullYear() &&
        a.getMonth() === b.getMonth() &&
        a.getDate() === b.getDate();
}


function searchMostCommonNumber(arr) {
    if (arr === void 0) {
        arr = [];
    }
    var current = 0;
    var max = 0;
    var mostCommonNumber = 0;
    var i;
    for (i = 0; i < arr.length - 1; i++) {
        var current_1 = 1;
        var j = void 0;
        for (j = i + 1; j < arr.length; j++) {
            if (arr[i] === arr[j]) {
                current_1++;
            }
        }
        if (current_1 > max) {
            max = current_1;
            mostCommonNumber = arr[i];
        }
    }
    return mostCommonNumber;
}