Edit in JSFiddle

$("#toggle-button").click(function(){
	$("#toggle-content").fadeToggle(1000, function(){
		if($(this).css("display") === "none"){
			$("#toggle-button").html("Muuda kast nähtavaks");
		}else{
			$("#toggle-button").html("Muuda kast nähtamatuks");
		}
	});
});
#toggle-content{
	color: white;
	background-color: black;
	width: 100px;
	height: 100px;
}
<button type="button" id="toggle-button">Muuda kast nähtamatuks</button>
<div id="toggle-content">Sisu siin</div>