Showing number of slides on the web page

I wrote a custom slider as shown in this codepen:
http://codepen.io/anon/pen/NqQpjG
I added extra feature which counts total number of slides that are moved. For example, if total slides are 8, then starting value would be like this:
Slides: 0/8. When one slide moves, it becomes Slides: 1/8 and so on. Here is my code:

<div>
            <span id="numberSlides">0/0 Offers</span>
        </div>

JS

var slide = new slide('.swiper-slide', {
        var totalSlides = 10;
        var newSlide = document.getElementsByClassName('swiper-slide');
        var newValue = newSlide + 1;
        document.getElementById('numberSlides').innerHTML = newValue + "/" + totalSlides + " Slides";
    });

But it isn't working. How can I display the number of slides that are moved?
EDIT:
My slides are in these divs:

<div class="swiper-container">
        <div class="swiper-wrapper">
            <div class="swiper-slide">Slide 1</div>
            <div class="swiper-slide">Slide 2</div>
            <div class="swiper-slide">Slide 3</div>
            <div class="swiper-slide">Slide 4</div>
            <div class="swiper-slide">Slide 5</div>
            <div class="swiper-slide">Slide 6</div>
            <div class="swiper-slide">Slide 7</div>
            <div class="swiper-slide">Slide 8</div>
            <div class="swiper-slide">Slide 9</div>
            <div class="swiper-slide">Slide 10</div>
        </div>
        <!-- Add Pagination -->
        <div class="swiper-pagination"></div>
    </div>

Solution

Use this properties

  runCallbacksOnInit: true, 
  onInit: function(sw){}, //runs callback in initialization
  onSlideChangeEnd: function(sw){} //runs callback in slide change end

Demo

var swiper = new Swiper('.swiper-container', {
  pagination: '.swiper-pagination',
  paginationClickable: true,
  nextButton: '.swiper-button-next',
  prevButton: '.swiper-button-prev',
  spaceBetween: 30,
  centeredSlides: true,
  autoplay: 3000,
  autoplayDisableOnInteraction: false,
  runCallbacksOnInit: true,
  onInit: function(sw){
    var offer = document.querySelector('#numberSlides');
    offer.innerHTML = (sw.activeIndex +  1) + '/' + sw.slides.length + 'Offers';
  },
  onSlideChangeEnd: function(sw){
    var offer = document.querySelector('#numberSlides');
    offer.innerHTML = (sw.activeIndex +  1) + '/' + sw.slides.length + 'Offers';
  }
});

#numberSlides{
  position: absolute; 
  bottom: 0;
  left: 0;
  z-index: 9999;
}

html,
body {
  position: relative;
  height: 100%;
}

body {
  background: #eee;
  font-family: Helvetica Neue, Helvetica, Arial, sans-serif;
  font-size: 14px;
  color: #000;
  margin: 0;
  padding: 0;
}

.swiper-container {
  width: 100%;
  height: 100%;
}

.swiper-slide {
  text-align: center;
  font-size: 18px;
  background: #fff;
  /* Center slide text vertically */
  
  display: -webkit-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  -webkit-justify-content: center;
  justify-content: center;
  -webkit-box-align: center;
  -ms-flex-align: center;
  -webkit-align-items: center;
  align-items: center;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/Swiper/3.1.2/js/swiper.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/Swiper/3.1.2/css/swiper.css">
<div class="swiper-container">
  <div class="swiper-wrapper">
    <div class="swiper-slide">Slide 1</div>
    <div class="swiper-slide">Slide 2</div>
    <div class="swiper-slide">Slide 3</div>
    <div class="swiper-slide">Slide 4</div>
    <div class="swiper-slide">Slide 5</div>
    <div class="swiper-slide">Slide 6</div>
    <div class="swiper-slide">Slide 7</div>
    <div class="swiper-slide">Slide 8</div>
    <div class="swiper-slide">Slide 9</div>
    <div class="swiper-slide">Slide 10</div>
  </div>
  <!-- Add Pagination -->
  <div class="swiper-pagination swiper-pagination-clickable"></div>
  <div id="numberSlides">
    0/0 Offers
  </div>
</div>