jquery ui datepicker if no active mondays left at the end of the month

Question

I made that only mondays are active in each month like this

function onlyMondays(date){
        var day = date.getDay();                    
        return [(day == 1), ''];                                                        
    }

But at last week of the month there wont be any active mondays left so i want to show next month in that case based on the code above.

Any idea would be appreaciated. Thanks.