JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://momentjs.com/downloads/moment-with-langs.js"></script>

JavaScript

var startdate = moment('2014-01-03');
var enddate = moment('2014-01-05');

var obj = {};
obj['2014-01-02'] = '2';
obj['2014-01-03'] = '3';
obj['2014-01-04'] = '4';
obj['2014-01-05'] = '5';
obj['2014-01-06'] = '6';

var strDate;
var total = 0;
for (strDate in obj) {
    if (obj.hasOwnProperty(strDate)) {
        var date = moment(strDate)
        if (date.diff(startdate, 'days')>=0 && date.diff(enddate, 'days')<=0) {
            total += parseInt(obj[strDate], 10);
        }
    }
}

console.log(total);