app.js

$(document).ready(function() {

	$(document.documentElement).keypress(function(event) {
		if (event.which == 37) {
			$('.slider ul a.current').removeClass('current').parent() // moves up to the li element
			.prev() // moves to the adjacent li element
			.find('a') // moves down to the link
			.addClass('current'); // triggers a click on the previous link
		} else if (event.which == 39) {
			// go right
			$('.slider ul a.current').removeClass('current').parent().next().find('a').addClass('current');
		}
	});

});

index.html

<div class="slider">
  <ul>
    <li><a class="current" href="#1">1</a></li>
    <li><a href="#2">2</a></li>
    <li><a href="#3">3</a></li>
    <li><a href="#4">4</a></li>
    <li><a href="#5">5</a></li>
  </ul>
</div>