Как вернуть переменную из функции?

function Slider(obj) {
    this.images = obj.images;
    this.autoplayInterval = obj.autoplayInterval;
    this.defaultSlide = obj.defaultSlide;
    this.autoplaySpeed = obj.autoplaySpeed;

    this.init();
}

Slider.prototype.init = function () {
  var currentSlide = this.defaultSlide || 1;
  var sliderContainer = $(".slider-container");

  for (var i = 0; i < this.images.length; i++) {
    var slideNumber = i + 1;
    var divElem = document.createElement("div");

    divElem.classList.add("slider-item");
    divElem.classList.add("slide-" + slideNumber);

    if (slideNumber == this.defaultSlide) {
      divElem.classList.add("slide-active");
    }

    divElem.style.backgroundImage = 'url(' + this.images[i] + ')';
    sliderContainer.append(divElem);
  }

  if (obj.autoplay) {
    setInterval(this.changeSlide.bind(this), this.autoplayInterval);
  }
}

Slider.prototype.changeSlide = function () {
    if (this.currentSlide === this.images.length) {
        currentSlide = 1;
    } else {
        this.currentSlide++;
    }
}