Get -30 days from a date

gistfile1.js

var actualDate = new Date(2009,02,31);

var date = actualDate.getDate().toString();
var month = actualDate.getMonth().toString();
var year = actualDate.getFullYear().toString();

var testDate = new Date(year, month, date);

console.log("Antes");
console.log(actualDate);
console.log(testDate);

testDate.setDate(actualDate.getDate()+1);

if(testDate.getMonth() !== actualDate.getMonth()){
    console.log("Ultimo dia");
    var lastMonth = new Date(year, month, 1);
    lastMonth.setMonth(lastMonth.getMonth());
    lastMonth.setDate(0);
}
else{
    console.log("Nem é");
    var lastMonth = new Date(year, month, date);
    lastMonth.setMonth(lastMonth.getMonth()-1);
}

console.log("Depois");
console.log(actualDate);