Modal Form Submit Button Not Working When Clicked

I created a modal dropdown form with four dropdown lists, with the fourth dropdown containing a link to a document to display once user clicks the submit button. All four dropdowns work fine, however when clicking the submit button the document does not display. The form simply continues to display, log indicates 'Cannot read property '0' of undefined'.. Any help is appreciated.

var selectedOptions = {};

        $('#link1').on('change', function () {
            var a = $(this).val();
            selectedOptions['1'] = a;
            selectedOptions['2'] = a;
            selectedOptions['3'] = a;
            if (a !== '') {
                for (var i = 0; i < dataSecondSelect[a].length; i++) {
                    $('#link2').append($("<option></option>")
                            .attr("value", dataSecondSelect[a][i])
                            .text(dataSecondSelect[a][i]));
                }
            }
        });

        $('#link2').on('change', function () {
            var a = $(this).val();
            selectedOptions['1'] = a;
            selectedOptions['2'] = a;
            selectedOptions['3'] = a;
            if (a !== '') {
                for (var i = 0; i < dataThirdSelect[a].length; i++) {
                    $('#link3').append($("<option></option>")
                            .attr("value", dataThirdSelect[a][i])
                            .text(dataThirdSelect[a][i]));
                }
            }
        });
        $('#link3').on('change', function () {
            var a = $(this).val();
            selectedOptions['1'] = a;
            selectedOptions['2'] = a;
            selectedOptions['3'] = a;
            if (a !== '') {
                for (var i = 0; i < dataFourthSelect[a].length; i++) {
                    $('#link4').append($("<option></option>")
                            .attr("value", dataFourthSelect[a][i].link)
                            .text(dataFourthSelect[a][i].form));
                }
            }
        });

    $('#clickButton').on('click', function () {
        var error = false;
        $(".error").remove();
        $(".validation-error").removeClass('validation-error');
        $('#myModal select').each(function () {
            // validate first
            if ($(this).val() === "") {
                var _message = "Please select an option";
                $(this).addClass('validation-error');
                $(this).after($('<div class="error"></div>').text(_message));
                error=true;
            }
        });

        if (error) { return; }
        // form is now validated so get the link
        var _index = $("#link4").val();
        var _form = dataFourthSelect[_index][0].link;
        resetForm($(this)[0]);
        $('#myModal').modal('hide');
        openDoc(_form);

    });

    function resetForm(e) {
        $(".error").remove();
        $(".validation-error").removeClass('validation-error');
        e.form.reset();
    }

</script>

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