jQuery wordpress j/k next/prev navigation

jk-nav.js

// Simple J/k navigation for Wordpress
// by Alex Buznik (@beshur)
//
// Change t value for the correct selectors of the items that need to be traversed
(function($) {
	$(function() {
		var is_blog = true;
		if (!$("body").hasClass("blog")) {
			is_blog = false;
		}

		$(window).on("keyup", function(e) {
			if (e.which == 74 || e.which == 75) {

				// forward
				var dir = true;
				// backward
				if (e.which == 75) dir = false;

				var t = $("article > h2, article img, article iframe");
				if (is_blog) {
					t = $("article.post, article + .pagination");
				}

				var scrollTop = $(window).scrollTop();

				t.each(function(i) {
					var o = $(this).offset().top;

					if (o > scrollTop || o == scrollTop || i+1 == t.length) {
						var to = o;
						if (o == scrollTop && dir) {
							to = $(t[i+1]).offset().top;
						} else if (o == scrollTop && !dir) {
							if (i == 0) return false;
							to = $(t[i-1]).offset().top;
						}

						
						if (!dir) {
							to = $(t[i-1]).offset().top;
							if (o < scrollTop && i != 0) {
								to = $(this).offset().top;
							}
						} else {
							// if forward, post is last and position on last
							if (i+1 == t.length) return false;
						}
						

						$("html,body").stop(true, true).animate({
							scrollTop: to
						}, "fast");
						return false;
					}

				});

			}
		});
	});
});