JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.3/moment.min.js"></script>

JavaScript

var date = "07/09/15 13:56:57";
var offset = "-04:00";

var newDate = moment(date+offset);
var newDateString = newDate.utc().format();

alert(newDateString);