IF definitely doesn’t wok,

no one help me with this: Writing text and DarkMode don’t work together. So... I found a bug. But I don’t know, how I solve it. Please, if I complete if (dmTheme === detect), TypeWriting text doesn’t work. If I left there if (dmTheme === ) so if doesn’t work, but TypeWriting text yes. What of this little bit of darkMode code attack on TypeWritter?

window.onload = function checkCookie() {
  var dmTheme = getCookie("darkmode");
  var detect = "active";
  if (dmTheme === detect) {
   console.log("Darkmode is " + dmTheme);
   $("#switching").prop("checked", true);
   darkMode();
   $("#switching").prop("checked", true);
  } else {
    console.log("Darkmode is " + dmTheme);
    $("#switching").prop("checked", false);
  }
}

    var TxtType = function(el, toRotate, period) {
        this.toRotate = toRotate;
        this.el = el;
        this.loopNum = 0;
        this.period = parseInt(period, 10) || 2000;
        this.txt = '';
        this.tick();
        this.isDeleting = false;
    };

    TxtType.prototype.tick = function() {
        var i = this.loopNum % this.toRotate.length;
        var fullTxt = this.toRotate[i];

        if (this.isDeleting) {
        this.txt = fullTxt.substring(0, this.txt.length - 1);
        } else {
        this.txt = fullTxt.substring(0, this.txt.length + 1);
        }

        this.el.innerHTML = '<span class="wrap">'+this.txt+'</span>';

        var that = this;
        var delta = 200 - Math.random() * 100;

        if (this.isDeleting) { delta /= 2; }

        if (!this.isDeleting && this.txt === fullTxt) {
        delta = this.period;
        this.isDeleting = true;
        } else if (this.isDeleting && this.txt === '') {
        this.isDeleting = false;
        this.loopNum++;
        delta = 500;
        }

        setTimeout(function() {
        that.tick();
        }, delta);
    };

    window.onload = function() {
        var elements = document.getElementsByClassName('typewrite');
        for (var i=0; i<elements.length; i++) {
            var toRotate = elements[i].getAttribute('data-type');
            var period = elements[i].getAttribute('data-period');
            if (toRotate) {
              new TxtType(elements[i], JSON.parse(toRotate), period);
            }
        }
        
        var css = document.createElement("style");
        css.type = "text/css";
        css.innerHTML = ".typewrite > .wrap { border-right: 0.08em solid #fff}";
        document.body.appendChild(css);
    };