epoch.js

var Utils = {
    //...

    /**
     * Convert a date/timestamp to an epoch timestamp
     *
     * @param   {Date|string}   date        Either a date in string format, or a Date object
     * @param   {string}        round       Since the date inputs are day specific (no hour/minute/second), 
     *                                      this dictates if it will be rounded up or down. Allowed values are "start", "stop", "up" and "down"
     * @param   {string}        dateFormat  Dates input format (default is "mm/dd/yy")
     * @returns {string}        Returns the timestamp in epoch format
     * @examples
     *      Utils.convertToEpoch( '08/03/2016' )                     // 1470207600
     *      Utils.convertToEpoch( '08/03/2016', 'up' )               // 1470294000
     *      Utils.convertToEpoch( '08/03/2016', 'down' )             // 1470121200
     *      Utils.convertToEpoch( '08/2016/03', 'down', "mm/yy/dd" ) // 1470121200
     */
    convertToEpoch: function( date, round, dateFormat ){
        var dFormat = ( typeof dateFormat === 'string' ? dateFormat : "mm/dd/yy" ),
            GMT = true, 
            date_day,
            dDate

        // If the date provided isn't a string or already a date, then throw an error
        if( $.inArray( date.constructor.name, [ 'Date', 'String' ] ) === -1 ){
            throw "convertToEpoch expected the date parameter to be a String or Date - received: " + date.constructor.name
        }

        // If its a string, then try to convert it to a date using the datepickers parseDate
        else if( date.constructor.name === 'String' ){
            dDate = $.datepicker.parseDate( dFormat, date )
        }

        // Only other scenario is that date is already a Date object, so just use it
        else {
            dDate = date
        }

        if( round === 'start' || round === 'down' )
            date_day = dDate.getUTCDate()-1
        else if( round === 'stop' || round === 'up' )
            date_day = dDate.getUTCDate()+1
        else
            date_day = dDate.getUTCDate()

        //date_day = dDate.getUTCDate()
        if(GMT){ 
            var x = parseInt(Date.UTC(dDate.getUTCFullYear(),dDate.getUTCMonth(),date_day,dDate.getUTCHours(),dDate.getUTCMinutes(),dDate.getUTCSeconds(),dDate.getUTCMilliseconds())/1000)
            return x
        } else {
            var x = ( dDate.getTime()-dDate.getMilliseconds() )/1000
            //    x += dDate.getTimezoneOffset();
            return x
        }
    }

    //...
}