Copy your current chat input to clipboard as rot13-encoded text in Twitch

rot13button.user.js

// ==UserScript==
// @name         Rot13 Encode Chatbox to Clipboard
// @namespace    https://gist.github.com/awsr
// @version      0.3.0
// @description  Encode message in chatbox and copy to clipboard
// @author       Tenosis
// @downloadURL  https://gist.github.com/awsr/eb3c6c16f3aaf62e87e345acf1bbff3a/raw/rot13button.user.js
// @match        https://www.twitch.tv/*
// @grant        none
// ==/UserScript==

(function () {
  'use strict';

  let startupLoops = 0;

  const scriptCSS = document.createElement("style");
  scriptCSS.textContent = `
  .userscript-button13 {
    position: relative;
    display: flex;
    flex-flow: column nowrap;
    flex-grow: 1;
    height: 100%;
    color: var(--color-text-base);
  }
  .userscript-button13 button {
    position: relative;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    user-select: none;
    height: var(--button-size-default);
    width: var(--button-size-default);
    border-radius: var(--border-radius-medium);
    background-color: var(--color-background-button-text-default);
    color: var(--color-fill-button-icon);
    font-size: var(--button-text-default);
    font-weight: var(--font-weight-semibold);
    text-decoration: none;
    vertical-align: middle;
    overflow: hidden;
  }
  .userscript-button13 button:active {
    background-color: var(--color-background-button-text-active);
    color: var(--color-fill-button-icon-active);
  }
  .userscript-button13 button:hover {
    background-color: var(--color-background-button-text-hover);
    color: var(--color-fill-button-icon-hover);
  }
  `;
  document.head.append(scriptCSS);

  function rot13(message) {
    return message.replace(/[a-z]/gi, letter => String.fromCharCode(letter.charCodeAt(0) + (letter.toLowerCase() <= 'm' ? 13 : -13)));
  }

  function buttonHandler() {
    let chatText = document.querySelector("[data-a-target=chat-input-text]")?.innerText;
    if (chatText && !(/\n/.test(chatText) && chatText.length === 2)) {
      chatText = rot13(chatText);
      navigator.clipboard.writeText(chatText);
    }
  }

  const rot13div = document.createElement("div");
  rot13div.classList.add("userscript-button13");
  const rot13button = document.createElement("button");
  rot13button.innerText = "13";
  rot13div.appendChild(rot13button);
  rot13button.addEventListener("click", buttonHandler);

  function startup() {
    let chatButtons = document.querySelector(".chat-input__buttons-container > div:last-child");
    if (chatButtons) {
      clearInterval(startupChecker);
      chatButtons.insertAdjacentElement("afterbegin", rot13div);
    } else {
      startupLoops++;
      if (startupLoops > 10) {
        clearInterval(startupChecker);
      }
    }
  }

  const startupChecker = setInterval(startup, 2000);
})();