Scroll to the next diff in a PR summary window!

diff-scroller.js

(function($, w, undefined) {
	var $diffs = $('.diff-view .js-details-container');
	var $comments = $('.diff-view .js-comment');
	var $w = $(w);
	var $a = $('<a/>', {
		'class': 'js-next-diff',
		'href': '#'
	}).css({
		'position': 'fixed',
		'font-size': 'large',
		'display': 'block',
		'padding': '1rem',
		'text-transform': 'uppercase',
		'top': 0,
		'right': 0
	}).text('Next').on('click', function(ev) {
		ev.preventDefault();
		goToNext($diffs);
	});
	$(document.body).append($a).on('keydown', function(ev) {
		//if the event came from an input box, we don't want to scroll
		if ($(ev.target).is(':input')) {
			return true;
		}
		if (ev.which == 74) {
			goToNext($diffs);
		}
		else if (ev.which == 75) {
			goToPrev($diffs);
		}
		else if (ev.which == 78) {
			goToNext($comments);
		}
		else if (ev.which == 77) {
			goToPrev($comments);
		}
	});
	function goToNext($els) {
		var scrollTop = $w.scrollTop() + 5;
		$els.each(function() {
			var offsetTop = $(this).offset().top;
			if (offsetTop > scrollTop) {
				$('html,body').animate({scrollTop: offsetTop});
				return false;
			}
		});
	}
	function goToPrev($els) {
		var scrollTop = $w.scrollTop() - 5;
		var prev;
		$els.each(function() {
			var offsetTop = $(this).offset().top;
			if (offsetTop >= scrollTop) {
				//don't animate here, because if we loop through all of them
				// we want the last item to be animated to
				return false;
			}
			prev = offsetTop;
		});
		//animate to the last "prev"
		$('html,body').animate({scrollTop: prev});
	}
})(jQuery, window);

This bookmarklet appears to work:

javascript:(function(e,t,n){var r=e(".js-diff-view .js-details-container");var i=e(t);var s=e("<a/>",{"class":"js-next-diff",href:"#"}).css({position:"fixed","font-size":"large",display:"block",padding:"1rem","text-transform":"uppercase",top:0,right:0}).text("Next").on("click",function(t){t.preventDefault();var n=i.scrollTop();r.each(function(){var t=e(this).offset().top;if(t>n){e("html,body").animate({scrollTop:t});return false}})});e(document.body).append(s).on("keydown",function(t){if(e(t.target).is(":input")){return true}if(t.which==74){s.click()}else if(t.which==75){var n=i.scrollTop();var o;r.each(function(){var t=e(this).offset().top;if(t>=n){return false}o=t});e("html,body").animate({scrollTop:o})}})})(jQuery,window)