JQUERY - Trail navigator

gistfile1.js

// HTML

<div id="mattress_slider">
    <div class="mattress_container">
        <div class="mattress_slider">
            <div class="product-list-item"></div>
            <div class="product-list-item"></div>
            <div class="product-list-item"></div>
            ...
        </div>
    </div>
		
</div>

// LESS

#mattress_slider{
    position:relative;
    .mattress_container{
        overflow:hidden;
        position:relative;
        height: 292px;
    }
    .mattress_slider{
        position: absolute;
        top:0;
        left:0;
        height: 252px;
    }
    .previous{
        position: absolute;
        text-decoration: none;
        background-image: url('/media/img/arrow-left.png');
        background-repeat: no-repeat;
        display: block;
        width:20px;
        height:54px;
        opacity:0.7;
        &:hover{
            opacity:1;
        }
    }
    .next{
        position: absolute;
        text-decoration: none;
        background-image: url('/media/img/arrow-right.png');
        background-repeat: no-repeat;
        display: block;
        width:20px;
        height:54px;
        opacity:0.7;
        &:hover{
            opacity:1;
        }
    }
}

//JS

//Mattress slider
//Mattress slider
$('#mattress_slider').append('<a href="#" class="previous"></a>');
$('#mattress_slider').append('<a href="#" class="next"></a>');

// How manay mattresses
var mattress_count = $('#mattress_slider .product-list-item').length;
var mattress_width = $('#mattress_slider .product-list-item').width();
var slider_width = $('#mattress_slider').width();
// How manay fit in slider
var fits = slider_width / mattress_width;
// How manay are missing
var hidden = mattress_count - fits;

// Adjust slider
$('.mattress_slider').css({'width':mattress_count * mattress_width});


 // Position arrows
$('#mattress_slider .previous').hide().css({'top':100, 'left':-34}).click(function(e){
    e.preventDefault()
    if(hidden < (mattress_count - fits)){
        var passed = mattress_count - fits - hidden;
        // Shift slider by one
        $('.mattress_slider').stop().animate({'left': ((1-passed) * mattress_width)}, 500);
        // Decrement hidden
        hidden += 1;
    }
    // Show or hide controls accordingly
    show_hide_controls();
})
$('#mattress_slider .next').css({'top':100, 'right':-34}).click(function(e){
    e.preventDefault()
    if(hidden > 0){
        var passed = mattress_count - fits - hidden;
        // Shift slider by one
        $('.mattress_slider').stop().animate({'left': -((1+passed) * mattress_width)}, 500);
        // Decrement hidden
        hidden -= 1;
    }
    // Show or hide controls accordingly
    show_hide_controls();
})

function show_hide_controls(){
    if(hidden == 0) $('#mattress_slider .next').hide();
    else $('#mattress_slider .next').show();

    if(hidden == mattress_count - fits) $('#mattress_slider .previous').hide();
    else $('#mattress_slider .previous').show();
}