Shorter version of Jeffrey Way's jQuery slider done in episode 15 of Learn jQuery in 30 days

Slider-shorter.js

(function($) {
	var sliderUL = $('div.slider').css('overflow', 'hidden').children('ul'),
		imgs = sliderUL.find('img'),
		imgWidth = imgs[0].width, // 600
		imgsLen = imgs.length, // 4
		current = 0, //0: first

	$('#slider-nav').show().find('button').on('click', function() {
		var direction = $(this).data('dir'),
			move = ( direction === 'next' ) ? 1 : -1; //1 forward, -1 backward
		
		current += move;
		current = (current >= 0) ? (current % imgsLen) : (imgsLen-1); 
		sliderUL.animate({
			'margin-left': -current*imgWidth
		});
	});
})(jQuery);