jquery fade out

                                    if (!Element.prototype.fadeIn) {
    Element.prototype.fadeIn = function(){
        let ms = !isNaN(arguments[0]) ? arguments[0] : 400,
            func = typeof arguments[0] === 'function' ? arguments[0] : (
                typeof arguments[1] === 'function' ? arguments[1] : null
            );

        this.style.opacity = 0;
        this.style.filter = "alpha(opacity=0)";
        this.style.display = "inline-block";
        this.style.visibility = "visible";

        let $this = this,
            opacity = 0,
            timer = setInterval(function() {
            opacity += 50 / ms;
            if( opacity >= 1 ) {
                clearInterval(timer);
                opacity = 1;

                if (func) func('done!');
            }
            $this.style.opacity = opacity;
            $this.style.filter = "alpha(opacity=" + opacity * 100 + ")";
        }, 50 );
    }
}

if (!Element.prototype.fadeOut) {
    Element.prototype.fadeOut = function(){
        let ms = !isNaN(arguments[0]) ? arguments[0] : 400,
            func = typeof arguments[0] === 'function' ? arguments[0] : (
                typeof arguments[1] === 'function' ? arguments[1] : null
            );

        let $this = this,
            opacity = 1,
            timer = setInterval( function() {
            opacity -= 50 / ms;
            if( opacity <= 0 ) {
                clearInterval(timer);
                opacity = 0;
                $this.style.display = "none";
                $this.style.visibility = "hidden";

                if (func) func('done!');
            }
            $this.style.opacity = opacity;
            $this.style.filter = "alpha(opacity=" + opacity * 100 + ")";
        }, 50 );
    }
}

// fadeIn with default: 400ms
document.getElementById(evt.target.id).fadeIn();

// Calls the "alert" function with the message "done!" after 400ms - alert('done!');
document.getElementById(evt.target.id).fadeIn(alert);

// Calls the "alert" function with the message "done!" after 1500ms - alert('done!');
document.getElementById(evt.target.id).fadeIn(1500, alert);

                                    	$('.btn-cart').click(function(e) {
		e.preventDefault();
		$('.cartlist').fadeIn().addClass('active');
	});

	$('.btn-cartlist-close').click(function() {
		$('.cartlist').removeClass('active').fadeOut();
	});

                                    $(selector).fadeOut(duration)
$(selector).fadeIn(duration)

                                    $(".example").fadeIn(500);

                                    $(document).ready(function(){
  $("button").click(function(){
    $("p").fadeOut();
  });
});