Hacker News Comment Hiding

hacker_hiding.user.js

// ==UserScript==
// @name           Hacker News Comment Hiding
// @namespace      http://drostie.org/
// @include        https://news.ycombinator.com/item?id=*
// @include        http://news.ycombinator.com/item?id=*
// ==/UserScript==

function repeat(element, selector, n) {
    return n <= 0 ? element : repeat(element[selector], selector, n - 1);
}
var comments_hidden = "\u25B9", // unicode: "white right-pointing small triangle"
    comments_shown = "\u25BF"; // unicode: "white down-pointing small triangle"

function indent_level(block) {
    return block === null ? -1 : repeat(block, 'firstChild', 6).width;
}
[].forEach.call(document.getElementsByClassName("comment"), function (comment) {
    var block = repeat(comment, 'parentNode', 6),
        indent_comment = indent_level(block),
        ratings = comment.parentNode.previousSibling.firstChild,
        showing = true,
        link = document.createElement("a"),
        child_blocks = [];
    block = block.nextSibling;
    while (indent_level(block) > indent_comment) {
        child_blocks.push(block);
        block = block.nextSibling;
    }
    // logic should work, but don't display the link if no children
    if (child_blocks.length === 0) {
        return;
    }
    link.setAttribute("href", "#");
    link.innerHTML = comments_shown;
    link.onclick = function () {
        if (showing) {
            child_blocks.forEach(function (c) {
                if (!c.hidden_by) {
                    c.hidden_by = comment;
                    c.style.display = "none";
                }
            });
            link.innerHTML = comments_hidden;
            showing = false;
        } else {
            child_blocks.forEach(function (c) {
                if (c.hidden_by === comment) {
                    c.hidden_by = undefined;
                    c.style.display = "block";
                }
            });
            link.innerHTML = comments_shown;
            showing = true;
        }
        return false;
    };
    ratings.appendChild(document.createElement("br"));
    ratings.appendChild(link);
});