Javascript - Get Previous Months Date

Question

If i have a variable that returns a date, in the format of dd MMM yyyy, so 28 Aug 2014, how can i get the date of the previous month.

I can modify the month via:

$scope.DateMapping = function (months) {

    var myVariable = "28 Aug 2014"
    var makeDate = new Date(myVariable);
    prev = new Date(makeDate.getFullYear(), makeDate.getMonth()+1, 1);

});

Essentially, this is adding one to the Month.. But how can i account for years, so if the current date is 12 Dec 2014, the previous would be 12 Jan 2013?

My application is using AngularJS can make use of filters.

UPDATE:

    var myVariable = "28 Aug 2014"
    var makeDate = new Date(myVariable);
    var prev = new Date(makeDate.getFullYear(), makeDate.getMonth()+1, makeDate.getMonth());

    console.log(myVariable)
    console.log(makeDate)
    console.log(prev)

Output:

    28 Aug 2014
    Thu Aug 28 2014 00:00:00 GMT+0100 (GMT Standard Time)
    Mon Sep 01 2014 00:00:00 GMT+0100 (GMT Standard Time)

How comes although the month has incremented, the day is showing as 01 instead of 28?

Answer 1

var myVariable = "28 Aug 2014"
var makeDate = new Date(myVariable);
makeDate = new Date(makeDate.setMonth(makeDate.getMonth() - 1));

Update:

A shorter version:

var myVariable = "28 Aug 2014"
var makeDate = new Date(myVariable);

console.log('Original date: ', makeDate.toString());

makeDate.setMonth(makeDate.getMonth() - 1);

console.log('After subtracting a month: ', makeDate.toString());

Update 2:

If you don't want to deal with corner cases just use moment.js. Native JavaScript API for Date is bad.

Answer 2

Just subtract the number of months from the month parameter and don't worry if the value is going to be negative. It will be handled correctly.

new Date(2014, 0, 1) // 1st Jan 2014
new Date(2014, -1, 1) // 1st Dec 2013

Answer 3

For all date related activities I recommend using the moment.js library and as you are using AngularJS there is a library for this: https://github.com/urish/angular-moment.

Take a look at the moment.js documentation and you will see it makes it much easier to manipulate dates in JavaScript: http://momentjs.com/docs/#/get-set/month/

You will easily be able to solve the problem you are facing, for example:

var now = moment('01/01/2014').subtract(1, 'months').format('DD/MM/YYYY');

now would then equal 01/12/2013.