javascript – Calculate which days of the week the days of the month fall on

Question:

I created a javascript function that assembles a schedule. I need this schedule to assemble according to the amount and the days of the week of the given month. Ex ( August 1st fell on a Tuesday ). I also need that when I change the month my schedule mounts according to the selected month. Follow the code.

Function that assembles my schedule

$(document).ready(function () {
    var str = '';
    var aux = 1;
    var tr = '';
    var tbl = $('#calendar');

    for (var i = 1; i < 32; i++) {

        if (aux == 1) {
            tr = '<tr>';
        }
        str += tr + '<td class="calendario btnExibirDetalhes" data-toggle="modal" data-target="#Modal" position="static">' + i + '</td>';
        if (aux == 7) {

            str = str + tr;
            aux = 0;
        }
        aux++;
        tr = '';
    }
    if (tr == '') {
        tr = '</tr>';
        str = str + tr
    }
    tbl.append(str);
});

Function that sets the current month

 $(document).ready(function () {
    monName = new Array("Janeiro",
                        "Fevereiro",
                        "Março",
                        "Abril",
                        "Maio",
                        "Junho",
                        "Julho",
                        "Agosto",
                        "Setembro",
                        "Outubro",
                        "Novembro",
                        "Dezembro")
    hoje = new Date();
    var preenchemes = $('#mes');
    preenchemes.append(monName[hoje.getMonth()]);

});

Answer:

I don't know if I understand, but if you're having difficulties getting the day of the week that your Dates are, you can use the Date.prototype.getDay() method that returns the day of the week value for the date, being:

Valor | Dia da semana
------|---------------
  0   |    Domingo
  1   |    Segunda
  2   |    Terça
  3   |    Quarta
  4   |    Quinta
  5   |    Sexta
  6   |    Sábado

For example:

var d = new Date();
var n = d.getDay();
document.getElementById("result").innerHTML = n;

<p id="result"></p>

Edit

As per comment you need:

• Knowing how many days there are in a given month – which you can do according to this post on SOen , like this:

function daysInMonth(month, year) {
  return new Date(year, month + 1 /* para ir a proximo */ , 0 /* para voltar ao ultimo dia do mês anterior*/ ).getDate();
}

var d = new Date();
var result = daysInMonth(d.getMonth(), d.getFullYear());
document.getElementById("result").innerHTML = result;

<p id="result"></p>

• And what day falls on the 1st of a given month, almost in the same idea, something like this:

function firstDayWeekInMonth(month,year) {
   return new Date(year, month, 1).getDay();
}

var d = new Date();
var result = firstDayWeekInMonth(d.getMonth(), d.getFullYear());
document.getElementById("result").innerHTML = result;

<p id="result"></p>

Note: Whenever you are manipulating Dates, remember that months are not base 0 ( 0-based ) .