slick's slider images load only after clicking a slick-arrow

I'm trying to implement Slider Syncing using slick library. I have an array of images called pictures coming from the backend. I loop over these images to populate them under my slider-for and slider-nav divs.

HTML code:

<head>
<style>

.slick-arrow {
    color: #666666;
    background: red;
}    
.slider-for {
    max-width: 960px;
    margin-left: auto;
    margin-right: auto;
    margin-top: 5%;
}  
.slider-nav h1 {
    display: inline-block;
}
.slider-nav .slick-slide {
    text-align: center;
    width: 337px;
}
.container {
  margin-bottom: 5%;
  margin-top: 5%;
}    

</style>   
<link rel="stylesheet" type="text/css" href="//cdn.jsdelivr.net/jquery.slick/1.5.7/slick.css"/>
<link rel="stylesheet" type="text/css" href="//cdn.jsdelivr.net/jquery.slick/1.5.7/slick-theme.css"/>
</head>
    <div class="container-fluid padding25">
      <h2>Pictures</h2>
          <div class="slider-for">
            <% var index = 0;%>
            <%_.each(pictures, function(picture) { %>

                <div>
                    <img src="<%=picture.pictureUrl%>" class="img-rounded" width="460" height="345"/>
                </div>
            <%
              index++;
              });
            %>
          </div>

            <div class="slider-nav">
                <%_.each(pictures, function(picture) { %>

                    <div>
                        <img src="<%=picture.pictureUrl%>" class="img-rounded" width="150" height="300"/>
                    </div>
                <%
                index++;
                });
                %>   
        </div> 

    <div class="row">
        <h2>Videos</h2>
     ...
    </div>
    </div>

javaScript:

<script type="text/javascript" src="/slick-1.5.7/slick/slick.min.js"></script>

<script type="text/javascript">
    $(document).ready(function(){
        console.log("inside docready");
          $('.slider-for').slick({
              slidesToShow: 1,
              slidesToScroll: 1,
              fade: true,
              asNavFor: '.slider-nav',     
          });


        $('.slider-nav').slick({
          slidesToShow: 3,
          slidesToScroll: 1,
          dots: true,    
          asNavFor: '.slider-for',
          dots: true,
          centerMode: true,
          centerPadding: '3%',    
          focusOnSelect: true,
        });

        $('.single-item').slick({
            dots: false,
            arrows: true,
        });
    });
</script>

Only one image is visible in the slider-nav on page load. On clicking left/right slick-arrow, the images appear properly. I tried to write the same code in jsFiddle. But I think it works well there (Not sure if its because I have refrained from using for loop there.)

Solution

Let me mention that this code of mine goes into a tab which is not active by default. I figured that the width calculation of the image divs is not happening when the tab becomes active. If this was the active tab by default when the page loads, it works fine and not otherwise. This is because bootstrap uses display:none to handle hidden tabs and its not possible to get the width of tabs with display:none. I found the solution here.

In my main page where all these tabs are being set up, I inserted this code:

.tab-content > .tab-pane,
.pill-content > .pill-pane {
    display: block;     /* undo display:none          */
    height: 0;          /* height:0 is also invisible */ 
    overflow-y: hidden; /* no-overflow                */
}
.tab-content > .active,
.pill-content > .active {
    height: auto;       /* let the content decide it  */
}

I followed the CSS solution to change the way hidden tabs are handled in bootstrap.