How to properly validate a file with jquery?

Question

JavaScript

I have bad code for sending.
When you select a file, it checks for the appropriate file type, if the type is suitable, you can send it, if not, it shows an error message and you cannot send the file.
If the correct file is selected, it is still impossible to send the file, how to solve this problem?

var filesExt = ['csv'];
    $('#addcontactsfile-contact_file').change(function () {
        var parts = $(this).val().split('.');
        if (filesExt.join().search(parts[parts.length - 1]) != -1) {
            $("#file-help").css('display', 'none');
            $("#file-submit").click(function () {
                $('#add-contacts-file').submit(true);
            });
        } else {
            $("#file-help").css('display', 'inline-block');
            $("#file-submit").click(function () {
                $('#add-contacts-file').submit(false);
            });
        }
    });