addTheAbilityToSortByRankOrCommentsOrPointsToTheHackerNewsMainPage.user.js

// ==UserScript==
// @name        Hacker News Post Sorter
// @namespace   .
// @include     https://news.ycombinator.com/
// @version     1
// @grant       none
// ==/UserScript==

HTMLCollection.prototype.forEach = Array.prototype.forEach;


function keySort(seq, key){
  function compare(a,b){
    if(a<b){return -1;}
    if(a>b){return 1;}
    return 0;
  }
  seq.sort((a,b)=>compare(key(a),key(b)));
}

function Story(titleNode, infoNode, spacerNode){
  this.titleNode = titleNode;
  this.infoNode = infoNode;
  this.spacerNode = spacerNode;
}

Story.prototype.getCommentCount = function(){
  var links = this.infoNode.getElementsByTagName("A");
  
  //not sure which link, if any, is the comments link.
  //iterate through them all looking for a reasonable match.
  for(var i = 0; i < links.length; i+=1){
    link = links[i];
    var groups = /(\d*) comments?/.exec(link.innerHTML);
    if (groups != null){
      return parseInt(groups[1]);
    }
  }

  //some posts don't have comments at all.
  return 0;
}

Story.prototype.getPoints = function(){
  var node = this.infoNode.getElementsByClassName("score")[0];
  if (node == undefined){return 0;}
  var groups = /(\d*) points?/.exec(node.innerHTML);
  if (groups == null){return 0;}
  return parseInt(groups[1]);
  
}

Story.prototype.getRank = function(){
  var rankNode = this.titleNode.getElementsByClassName("Rank")[0];
  return parseInt(rankNode.innerHTML.replace(/\D/g, ""));  
}

function rearrange(func){
  var table = document.getElementsByClassName("itemList")[0];
  var body = table.getElementsByTagName("tbody")[0];
  var rows = body.getElementsByTagName("tr");
  var stories = [];
  for(var i = 0; i < rows.length-2; i+=3){
    stories.push(new Story(rows[i], rows[i+1], rows[i+2]));
  }
  
  keySort(stories, func);
  
  
  while (body.firstChild) {
    body.removeChild(body.firstChild);
  }
  
  stories.forEach(function(story){
    body.appendChild(story.titleNode);
    body.appendChild(story.infoNode);
    body.appendChild(story.spacerNode);
  }); 
}

function makeRotaryButton(config){
  var button = document.createElement("A");
  var idx = 0;
  button.innerHTML = config[idx]["text"];
  
  button.onclick = function(){
    config[idx]["func"]();
    idx = (idx + 1) % config.length;
    button.innerHTML = config[idx]["text"];
  };
  
  return button
}

//this is kind of dumb... We want the label to indicate the effect that the last button press had.
//it's a little awkward that the functions don't match up with their descriptions.
//This makes it harder to rearrange the rotation order.
var button = makeRotaryButton([
  {text: "sorting by rank",     func: ()=>rearrange(s=>-s.getCommentCount())},
  {text: "sorting by comments", func: ()=>rearrange(s=>-s.getPoints())},
  {text: "sorting by points",   func: ()=>rearrange(s=>s.getRank())}
]);
  
var x = document.getElementsByClassName("pagetop")[0];
x.innerHTML += "| ";
x.appendChild(button);