Slick.js slider with thumbnails

gistfile1.js

$('.specs__slider').slick({
    dots: true,
    centerMode: true,
    focusOnSelect: true,
    arrows: false,
    customPaging: function(slider, i) {
        return '<div class="thumbnails">' +$(slider.$slides[i]).find('img').prop('outerHTML')+ '</div>';
    }
});