Scrolls Facebook wall posts with j/k key

fb_jk_scroll.user.js

// ==UserScript==
// @name           fb_jk_scroll
// @version        0.1
// @description    Scrolls wall posts with j/k key
// @include        http://www.facebook.com/*
// @require 	   http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js
// ==/UserScript==

$(document).ready(function(){

    var posts=document.getElementById("home_stream").childNodes;
    var barHeight=document.getElementById("blueBar").clientHeight;
    
    $(window).keydown(function(e){
	if(posts[posts.length-1]<$(window).scrollTop()){
	    posts=document.getElementById("home_stream").childNodes;
	}

	if(e.keyCode==74){//j key
	    scrollDown();
	}
	else if(e.keyCode==75){//k key
	    scrollUp();
	}
    });
    
    function scrollDown(){ 
	scrollTo(nearestIndex()+1); 
    }
    function scrollUp(){ 
	scrollTo(nearestIndex()-1); 
    }

    function scrollTo(index){
	if(index<0) index=0;
	else if(posts.length<=index) index=posts.length-1;
	$('html,body').animate({scrollTop: $("#"+posts[index].id).offset().top-barHeight+2},'fast');
    }

    function nearestIndex(){
	var coord=$(window).scrollTop();
	if(coord<$("#"+posts[0].id).offset().top-barHeight){
	    return -1;
	}
	
	for(var i=0;i<posts.length;i++){
	    var top=$("#"+posts[i].id).offset().top-barHeight;
	    var bottom=top+$("#"+posts[i].id).height();

	    if(top<=coord && coord<bottom) return i;
	}
	return posts.length-1;
    }
});