JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

JavaScript

var year = 2014;
var month_number = 3;
var firstOfMonth = new Date(year, month_number-1, 1);
var lastOfMonth = new Date(year, month_number, 0);
var firstDay = firstOfMonth.getDay();
if(firstDay == 7)
    firstDay = 1;
else
    firstDay += 1;
var used = firstOfMonth.getDay() % 7 + 1 + lastOfMonth.getDate();
$('div').html(Math.ceil( used / 7));