4ch code line numbers tampermonkey

// ==UserScript==
// @name         4chan /g/ code linenumbers
// @namespace    none
// @version      0.1
// @description  end the pain
// @author       You
// @match        https://boards.4chan.org/g/thread/*
// @grant        none
// ==/UserScript==
function GM_addStyle(css) {
    var head, style;
    head = document.getElementsByTagName('head')[0];
    if (!head) { return; }
    style = document.createElement('style');
    style.type = 'text/css';
    style.innerHTML = css;
    head.appendChild(style);
}

GM_addStyle ( `
span.lineNumber {
    color: #6E9B98;
}
` );
GM_addStyle ( `
button.toggle {
    font-size: 75%;
    font-family: inherit;
    padding: 0;
}
` );

function addLineNumbersForBlock(codeblock) {
    var breakRowFromOneBlock=codeblock.getElementsByTagName("br");
    var indent=breakRowFromOneBlock.length.toString().length
    var firstRowNum = document.createElement("SPAN");
    firstRowNum.className="lineNumber"
    firstRowNum.innerHTML="1"+" ".repeat(indent-1)+"|"
    codeblock.insertBefore(firstRowNum, codeblock.firstChild)
    for (var j=0; j < breakRowFromOneBlock.length; j++) {
        if(breakRowFromOneBlock.length===1){
            break;
        }

        var singleBR = breakRowFromOneBlock[j]
        var lineNumberElement = document.createElement("SPAN");
        lineNumberElement.className="lineNumber"
        var sub=(j+2).toString().length
        lineNumberElement.innerHTML=(j+2).toString()+" ".repeat(indent-sub)+"|"
        singleBR.parentNode.insertBefore(lineNumberElement, singleBR.nextSibling)

    }
}
function removeLineNumbersForBlock(codeblock) {
    while (codeblock.getElementsByClassName("lineNumber").length) { //seems excessive but better options removed every other element.
        codeblock.getElementsByClassName("lineNumber")[0].parentNode.removeChild(codeblock.getElementsByClassName("lineNumber")[0]);
    }
}
function buttonRemove(event){
    var btn=event.currentTarget;
    addLineNumbersForBlock(btn.previousSibling.previousSibling)
    btn.removeEventListener("click", buttonRemove);
    btn.addEventListener("click", buttonAdd);
}
function buttonAdd(event){
    var btn=event.currentTarget;
    removeLineNumbersForBlock(btn.previousSibling.previousSibling)
    btn.removeEventListener("click", buttonAdd);
    btn.addEventListener("click", buttonRemove);
}
(function() {
    'use strict';

    var codeblocks=document.getElementsByClassName("prettyprint prettyprinted")
    for (var i=0; i < codeblocks.length; i++) {
        addLineNumbersForBlock(codeblocks[i]);
        var button = document.createElement("BUTTON");
        button.type="button";
        button.className="toggle";
        button.innerHTML="Toggle Line numbers"
        button.addEventListener("click",buttonAdd);
        var space = document.createElement("BR");
        codeblocks[i].parentNode.insertBefore(button, codeblocks[i].nextSibling)
        codeblocks[i].parentNode.insertBefore(space, codeblocks[i].nextSibling)

    }
})();