Animate to an unknown height with jquery

unknow-height-animate.js

$(document).ready(function(){
	$('.js-show').click(function(){

		var id = $(this).attr('id');
		var el = $('.' + id);

		if ($(this).hasClass('open')){
			el.animate({height: '46px'}, 600);
		}
		else{
			curHeight = el.height();
    		autoHeight = el.css('height', 'auto').height();
			el.height(curHeight).animate({height: autoHeight}, 600, function(){
				el.height('auto'); // set height to auto for responsive sites
			});
		}
		$(this).toggleClass('open');
	});
});

DEMO: http://codepen.io/joanclaret/pen/KwyKzN

... or simply use Max-height instead of height : )

http://jsfiddle.net/thechrisjordan/3Fc7D/23/