fullcalendar: Uncaught TypeError: Cannot read property 'localeData' of undefined

Question

I'm trying to use fullcalendar and it keeps throwing this error. I have all the required files included which are:

fullcalendar.js
fullcalendar.css
moment.js

However I'm getting this following error:

Uncaught TypeError: Cannot read property 'localeData' of undefined
    at getMomentLocaleData (fullcalendar.js:2554)
    at locale (fullcalendar.js:2445)
    at Object.defineProperty.value (fullcalendar.js:2559)
    at __webpack_require__ (fullcalendar.js:30)
    at Object.defineProperty.value (fullcalendar.js:12499)
    at __webpack_require__ (fullcalendar.js:30)
    at Object.defineProperty.value (fullcalendar.js:7367)
    at __webpack_require__ (fullcalendar.js:30)
    at Object.defineProperty.value (fullcalendar.js:12109)
    at __webpack_require__ (fullcalendar.js:30)

Here is my initialization of fullcalendar:

window.onload = function () {

    $('#calendar').fullCalendar({
        handleWindowResize: true,
        defaultView: 'month',
        themeSystem: "bootstrap3",
        eventLimit: true,
        //navLinks: true, // enable clicking on different days
        week: true,
        day: true,
        agenda: true,
        basic: true,
        events: [
            {
                title: 'event1',
                start: '2017-11-01'
            },
            {
                title: 'Holiday',
                start: '2017-11-05',
                end: '2017-11-07'
            },
            {
                title: 'event3',
                start: '2017-11-09T12:30:00',
                allDay: false // will make the time show
            }
        ]
    })

    $(".fc-today-button").html('<i class="fa fa-calendar"></i>');
    $(".fc-prev-button").html('<i class="fa fa-arrow-left"></i>');
    $(".fc-next-button").html('<i class="fa fa-arrow-right"></i>');
}

The calendar displays fine but because of this error, any jQuery that needs to be ran after is not running because of this exception.

Any pointers?