How to make Fade during slideUp and slideDown?

Question

JavaScript

How to make Fade in this situation, I tried it through animate, it did not work, what are the options ??

$(".items .item").click(function() {
  $(".items .item").removeClass("active").eq($(this).index()).addClass('active');
  $(".hidden-block .item-content").slideUp().eq($(this).index()).slideDown();
});

Answer 1

$.fn.slideFadeToggle = function(speed, easing, callback) {
    return this.animate({
            opacity: 'toggle',
            height: 'toggle'
        },
        speed, easing, callback);
};

$("button").click(function() {
    $('.content').slideFadeToggle(800);
});

https://jsfiddle.net/y0u/59fso3ct/