JSFiddle - React, Tailwind, and code Playground

HTML

<input class="btnSaveParameters" id="btn_SaveCriteria" type="button" value="Save Subscription"/>

JavaScript

// this will atach btn_SaveCriteria_onclick to btn_SaveCriteria button.

    $(function() {
        $('#btn_SaveCriteria').click(function(){ btn_SaveCriteria_onclick(); });
    });


    // this is your unchanged function
    function btn_SaveCriteria_onclick() {


    //Testing if function fires:
    window.alert(5 + 6);

    var availableSelects = [];
    $("Select").each(function () {
        availableSelects.push($(this).attr("id"));
    });
    if ($("#" + availableSelects[1]).find(":selected").text() + $("#" + availableSelects[2]).find(":selected").text()+$("#" + availableSelects[2]).find(":selected").text() ==='AllAllAll') {
        $(".PageTitle").append("<div id='dialog' title='Parameter Warning'>You cannot select all for all 3 filters</div>");
        $("#dialog").dialog();

    } else {
    var t = document.getElementById("modal-form").cloneNode(true);
    t.style.display = "inline";

    var options = { title: "Add a Description to your Subscription", width: 500, height: 100, dialogReturnValueCallback: MyDialogClosed, html: t };//$('<div id="pgDiv"><form id="pgForm" method="post"><input type="text" name="Description" id="pgDescription>Description: </form></div>').get(0) };


    SP.SOD.execute('sp.ui.dialog.js', 'SP.UI.ModalDialog.showModalDialog', options);

    }
    }