How to get the last day of the previous month in Javascript or JQuery

Question

I have the following code to get the current day:

var month=new Array(12);
month[0]="January";
month[1]="February";
month[2]="March";
month[3]="April";
month[4]="May";
month[5]="June";
month[6]="July";
month[7]="August";
month[8]="September";
month[9]="October";
month[10]="November";
month[11]="December";

var d = new Date();
var curr_date;
if (d.getDate() == 1)
{
    curr_date = d.getDate();
}
else
{
    curr_date = d.getDate() - 1;
}

var curr_month = d.getMonth() + 1; //months are zero based
var curr_year = d.getFullYear();
var message_day = curr_year + "_" + curr_month + "_" + curr_date;
var sql_day = month[curr_month - 1].substring(0,3) + curr_date.toString() + curr_year.toString();

if (curr_date == "1")
    {
         document.write(sql_day + " " + message_day);
    }

This is great for getting the current day, but now i need to get the last day of the last month if it is the beginning of a new month.

right now this will produce:

Feb12012 2012_2_1

but what i need output is:

Jan312012 2012_1_31

Thanks

Answer 1

var d=new Date(); // current date
d.setDate(1); // going to 1st of the month
d.setHours(-1); // going to last hour before this date even started.

now d contains the last date of the previous month. d.getMonth() and d.getDate() will reflect it.

This should work on any date api that wraps c time.h.