How to subtract two angularjs date variables

I am fairly new to angularjs, but here it goes. I am able two dates through angularjs in the form dd/mm/yyyy, but what I need to do is somehow subtract the two dates to get the difference in days between the two. I created a jquery function to do this, but I don't know how to pass in the two dates to the function. So I was wondering if there was a different way to go about this?

I am trying to set up a trigger system depending on the number of days in between the two dates for certain things to be stylized. For example if it's within 10 days I want it to use style 1 and if its within 20 days use style 2 and so on.

Basic javascript way:

var d1 = new Date('01/16/2013');
var d2 = new Date('02/26/2013');
var milliseconds = d2-d1;
var seconds = milliseconds / 1000;
var minutes = seconds / 60;
var hours = minutes / 60;
var days = hours / 24;

Using one of the Date libraries (such as moment.js):

var d1 = moment("01/16/2013");
var d2 = moment("02/26/2013");
var days = moment.duration(d2.diff(d1)).asDays();

you simply convert date into timestamp and then subtract.

var Date1 = 08/16/2004;
var Date2= 10/24/2005;

var timestamp1 = new Date(Date1).getTime();
var timestamp2 = new Date(Date2).getTime();

var diff = timestamp1 - timestamp2


var newDate = new Date (diff);

You can use angular-moment to calculate the difference, using the amDifference filter:

Get the difference between two dates in milliseconds. Parameters are date, units and usePrecision. Date defaults to current date. Example:

<span>Difference: {{ dateFrom | amDifference : dateTo : 'days' }} days</span>

I'm also an angularjs novice but wouldn't you handle this by making properties available through your javascript view model?

For example have a style field that changes based on the date fields (ie style returns style 1 when if the difference is 10 days) and hopefully through the angularjs binding the updates will propagate to the screen.

I think the right term for this is a computed property or calculated property

EDIT

Not sure if this is what you're looking for but see fiddle for example of calculating date diff and changing a style all based off properties of the view model (scope)

scope.diff and scope.col are the 2 properties to bind to

http://jsfiddle.net/chrismoutray/wfjv6/

HTML

<script src="http://code.angularjs.org/0.10.4/angular-0.10.4.min.js" ng:autobind></script>
<div ng:controller="ComputedPropertiesCtrl">
    first date <input ng:model="firstdate"> second date <input ng:model="seconddate"> difference {{diff}}
    <div>when the difference is greater than 10 color changes to green</div>
    <div>eg set the second date to 15/01/2013</div>
    <div style="background-color:{{col}};"> State </div>
</div>

JS

function ComputedPropertiesCtrl() {
    var scope = this;
    scope.firstdate = '01/01/2013';
    scope.seconddate = '10/01/2013';
    scope.data_before = [];
    scope.differenceInDays = function() {

        var dt1 = scope.firstdate.split('/'),
            dt2 = scope.seconddate.split('/'),
            one = new Date(dt1[2], dt1[1]-1, dt1[0]),
            two = new Date(dt2[2], dt2[1]-1, dt2[0]);

        var millisecondsPerDay = 1000 * 60 * 60 * 24;
        var millisBetween = two.getTime() - one.getTime();
        var days = millisBetween / millisecondsPerDay;

        return Math.floor(days);      
    };
    scope.color = function() {
        return (scope.differenceInDays() > 10) ? 'green' : 'red';
    };

    scope.$watch('[firstdate, seconddate]', function(currScope,newVal,oldVal) {
        scope.data_before = oldVal;
        scope.diff = scope.differenceInDays();
    });

    scope.$watch('[firstdate, seconddate]', function(currScope,newVal,oldVal) {
        scope.data_before = oldVal;
        scope.col = scope.color();
    });
}

CSS

h2 { position: fixed; right: 10px; top: 10px; color: red; background:white;z-index:1000; }
input { width: 100px; }
div { margin: 10px; padding: 10px; }

This works, and here are 2 flawless javascript date functions you should never be without...

// Returns the days between a & b date objects...
function dateDiffInDays(a, b) {
    var _MS_PER_DAY = 1000 * 60 * 60 * 24;
    // Discard the time and time-zone information.
    var utc1 = Date.UTC(a.getFullYear(), a.getMonth(), a.getDate());
    var utc2 = Date.UTC(b.getFullYear(), b.getMonth(), b.getDate());
    return Math.floor((utc2 - utc1) / _MS_PER_DAY);
}

// Calculate how many days between now and an event...
function daysTill(e) {
    var eventE = new Date(e);
    var today =  new Date();
    return dateDiffInDays(today, eventE);
}