in assets/js/slick.js [1782:1806]
            imageToLoad.onload = function() {
                if (imageSrcSet) {
                    image
                        .attr('srcset', imageSrcSet );
                    if (imageSizes) {
                        image
                            .attr('sizes', imageSizes );
                    }
                }
                image
                    .attr( 'src', imageSource )
                    .removeAttr('data-lazy data-srcset data-sizes')
                    .removeClass('slick-loading');
                if ( _.options.adaptiveHeight === true ) {
                    _.setPosition();
                }
                _.$slider.trigger('lazyLoaded', [ _, image, imageSource ]);
                _.progressiveLazyLoad();
            };