HN comments timeline

hn_comments_timeline.user.js

// ==UserScript==
// @name           HN comments timeline
// @namespace      sendos
// @description    Moves through HN comments chronologically, using the right and left arrow keys
// @include        http://news.ycombinator.com/item?id=*
// ==/UserScript==

function selectPost(new_idx)
{
    prev_post_idx    = current_post_idx;
    current_post_idx = new_idx % sortedPostInfo.length;
    if (current_post_idx < 0) { current_post_idx += sortedPostInfo.length; }

    window.scroll(0,sortedPostInfo[current_post_idx].value);
    var post  = document.getElementById(sortedPostInfo[current_post_idx].key);
    var idx   = current_post_idx+1;
    var descr = (idx==1) ? '' : (idx==2) ? '2nd ' : (idx==3) ? '3rd ' : idx+'th ';
    post.innerHTML += '<span style="border: 2px solid rgb(255, 0, 0);margin-left:5px;padding-right:5px;"> ' + descr + 'most recent post </span>';

    var prev_post = document.getElementById(sortedPostInfo[prev_post_idx].key);
    prev_post.innerHTML = prev_post.innerHTML.replace(/<span style=\"border: 2px solid rgb\(255, 0, 0\); *margin-left: *5px; *padding-right: *5px;\"> .*most recent post <\/span>/,"");
}

function detectArrows(evt) {
    evt = (evt) ? evt : ((window.event) ? window.event : null);

    if (evt) 
    {
        switch (evt.keyCode) 
	{
	   case 37: // Left arrow key
	        selectPost(current_post_idx-1);
                break;    
  	   case 39: // Right arrow key
	        selectPost(current_post_idx+1);
                break;    
         }
    }
};

var sortedPostInfo;
var current_post_idx  = -1;
var prev_post_idx     = -1;

(function() 
 {

     //Finds y value of given object
     function findPos(obj) 
     {
	 var curtop = 0;
	 if (obj.offsetParent) 
	 {
	     do { curtop += obj.offsetTop; }
	     while (obj = obj.offsetParent);
	     return [curtop];
	 }
     }

     function sortObj(object, sortFunc) 
     {
	 var rv = [];
	 for (var k in object) 
	 {
	     if (object.hasOwnProperty(k)) rv.push({key: k, value:  object[k]});
	 }
	 rv.sort(function(o1, o2) { return sortFunc(o1.key, o2.key); });
	 return rv;
     }

     var allPosts    = document.getElementsByClassName('comhead');
     var postInfo    = new Array();

     for (var i = 0; i < allPosts.length; i++)
     {
	 var post = allPosts[i];

	 if (post.innerHTML.match(/a href=\"item\?id=(\d+)\"/))
	 {
	     // Store post y-location and item id
	     var itemid = RegExp.$1; 
	     var ypos   = findPos(post);
	     post.id    = itemid;
	     
	     postInfo[itemid] = ypos;	     
	 }
	 else
	 {
	     //alert('problem with post ' + i + ': ' + post.innerHTML);
	 }
     }

     sortedPostInfo = sortObj(postInfo, function(a,b) {return b - a;});

     window.addEventListener('keyup', detectArrows, true);
     //document.onkeyup = detectArrows;
 })();