Javascript 上個月、本月、下個月

參考了網路寫了一個可直接設定第一天跟最後一天

//上個月
$(document).on('click', '#LastMonth', function () {                        
	SetLastAndFirstDate($('#fromdate').val(), -1);
})
//本月
$(document).on('click', '#ThisMonth', function () {            
	SetLastAndFirstDate($('#fromdate').val(), 0);
})
//下個月
$(document).on('click', '#NextMonth', function () {            
	SetLastAndFirstDate($('#fromdate').val(), +1);
})

function SetLastAndFirstDate(nowday, tomonth) {
	var date = new Date(nowday);

	if (tomonth == 0)
		var date = new Date();
	
	var firstDay = new Date(date.getFullYear(), date.getMonth() + (0 + tomonth), 1);
   var lastDay = new Date(date.getFullYear(), date.getMonth() + (1+tomonth), 0);
   $('#fromdate').val(formatDate(firstDay));//設定第一天
   $('#todate').val(formatDate(lastDay));//設定最後一天
   
}       

function formatDate(date) {
	var d = new Date(date),
	month = '' + (d.getMonth() + 1),
	day = '' + d.getDate(),
	year = d.getFullYear();
 	if (month.length < 2)
		month = '0' + month;
	if (day.length < 2)
	day = '0' + day;
	return [year, month, day].join('-');
}

參考來源
Format JavaScript date as yyyy-mm-dd
取得當月第一天和最後一天