How to get the 4 monday of a month with js?

Question

(first of all, excuse my english, i'm a beginner)

let me explain the situation :

I would like to create charts using Google Charts Tool (give it a try, it's very helpful). This part is not really difficult...

The problem comes when i have a specific chart requiring in the x-axis the four weeks of a month : i would like to display on the screen only the four mondays in the currentmonth.

I already have got the currentMonth and the currentYear variables and i know how to get the first day of the month. all i need is how to get the four mondays of a month, in an array. And all of this in the same JavaScript file.

I'm pretty lost within my programming logic, and i've seen plenty of solutions wich fit not my case.

so, what do i have is :

var date = new Date();
var currentYear = date.getFullYear();
var currentMonth = date.getMonth();
var firstDayofMonth = new Date(currentYear,currentMonth,1);
var firstWeekDay = firstDayofMonth.getDay();

and i would like to have something like this :

var myDates =
[new Date(firstMonday),new Date(secondMonday), new Date(thirdMonday),new Date(fourthMonday)]

Thank you for reading, and if you could help me... :)

Gaelle

Answer 1

The following function will return all Mondays for the current month:

function getMondays() {
    var d = new Date(),
        month = d.getMonth(),
        mondays = [];

    d.setDate(1);

    // Get the first Monday in the month
    while (d.getDay() !== 1) {
        d.setDate(d.getDate() + 1);
    }

    // Get all the other Mondays in the month
    while (d.getMonth() === month) {
        mondays.push(new Date(d.getTime()));
        d.setDate(d.getDate() + 7);
    }

    return mondays;
}

Answer 2

This would return the fourth last monday of month [m] in year [y]

function lastmonday(y,m) {
 var dat = new Date(y+'/'+m+'/1')
    ,currentmonth = m
    ,firstmonday = false;
  while (currentmonth === m){
    firstmonday = dat.getDay() === 1 || firstmonday;
    dat.setDate(dat.getDate()+(firstmonday ? 7 : 1));
    currentmonth = dat.getMonth()+1;
  }
  dat.setDate(dat.getDate()-7);
  return dat;
}
// usage 
lastmonday(2012,3); //=>Mon Mar 26 2012 00:00:00 GMT+0200
lastmonday(2012,2)  //=>Mon Feb 27 2012 00:00:00 GMT+0100
lastmonday(1997,1)  //=>Mon Jan 27 1997 00:00:00 GMT+0100
lastmonday(2012,4)  //=>Mon Apr 30 2012 00:00:00 GMT+0200

To be more generic, this will deliver the last any weekday of a month:

function lastDayOfMonth(y,m,dy) {
 var  days = {sun:0,mon:1,tue:2,wed:3,thu:4,fri:5,sat:6}
     ,dat = new Date(y+'/'+m+'/1')
     ,currentmonth = m
     ,firstday = false;
  while (currentmonth === m){
    firstday = dat.getDay() === days[dy] || firstday;
    dat.setDate(dat.getDate()+(firstday ? 7 : 1));
    currentmonth = dat.getMonth()+1 ;
  }
  dat.setDate(dat.getDate()-7);
  return dat;
 }
// usage 
lastDayOfMonth(2012,2,'tue'); //=>Tue Feb 28 2012 00:00:00 GMT+0100
lastDayOfMonth(1943,5,'fri'); //=>Fri May 28 1943 00:00:00 GMT+0200