Including script doesn't work but appending script tag to end does

The src value is relative to the current URL, make it absolute:

<script src="/js/parse_json.js"></script>

This block of code is placed directly after the body:

    <script src="/js/parse_json.js"></script>
    
    {{-- AJAX CALLS --}}

    <script>
        
        //DISCARD CHANGES
        $('#discard').click(function(event) {
            event.preventDefault();
            $.ajaxSetup({
                headers: {
                    'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
                }
            });

            Swal.fire({
                title: 'Are you sure?',
                text: "All changes will be lost!",
                icon: 'warning',
                showCancelButton: true,
                confirmButtonColor: '#3085d6',
                cancelButtonColor: '#d33',
                confirmButtonText: 'Yes',
                returnFocus: false,
                onAfterClose: () => window.scrollTo(0, 0)
            }).then((result) => {
                if (result.isConfirmed) {
                    $.ajax({
                        type: 'GET',
                        url: "{{ route('ajax.retrieve') }}",
                        data: {
                            id: $('#list').val()
                        },
                        success: function(data) {
                            parseFactSheet(data);
                            Swal.fire({
                                title: 'Reverted',
                                text: 'Changes have been reverted',
                                icon: 'success',
                                returnFocus: false,
                                onAfterClose: () => window.scrollTo(0, 0)
                            })
                        },
                        error: function() {
                            Swal.fire({
                                title: 'Error!',
                                text: 'Something went wrong.',
                                icon: 'danger',
                                returnFocus: false,
                                onAfterClose: () => window.scrollTo(0, 0)
                            })
                        }

                    })
                }
            });
        });

        //DISPLAY INFO

        $('#list').on('change', function(e) {

            $.ajaxSetup({
                headers: {
                    'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
                }
            });

            $.ajax({
                type: 'GET',
                url: "{{ route('ajax.retrieve') }}",
                data: {
                    id: $('#list').val()
                },
                success: function(data) {
                    parseFactSheet(data);
                }
            });
        });

        //SAVE CHANGES

        $('#save').click(function(event) {
            event.preventDefault();
            $.ajaxSetup({
                headers: {
                    'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
                }
            });


            $.ajax({
                type: 'POST',
                url: "{{ route('ajax.store') }}",
                data: {
                    id: $('#countryList').val(),
                    official_title: $('#official_title').val(),
                },

                success: function(data) {
                    var url = "http://127.0.0.1:8000/view/" + data.success['id'];
                    var xmlHttp = new XMLHttpRequest();
                    xmlHttp.open("GET", url, false);
                    xmlHttp.send();

                    var html = xmlHttp.responseText;

                    let [pre, middle] = html.split('typeof="WebPageElement">');
                    let [content, post] = middle.split('</main>')

                    //Create a blob of the data
                    var fileToSave = new Blob([content], {
                        type: 'text/plain;charset=utf-16'
                    });

                    saveAs(fileToSave, data.success['name'] + '.txt');

                    Swal.fire({
                        title: 'Your changes have been saved!',
                        text: "Updated HTML has been downloaded",
                        icon: 'success',
                        showCancelButton: false,
                        confirmButtonColor: '#3085d6',
                        confirmButtonText: 'OK',
                        returnFocus: false,
                        onAfterClose: () => window.scrollTo(0, 0)
                    });

                }

            });

        });
    </script>

The function (parseFactSheet) is first called within the Display info block.

It is loading, the response code is 200 and it looks good. it is simply defined with

function parseFactSheet(country){

...

}