Switch casing

case.js

(() => {
  let activeMode = "default";
  const modes = {
    default: (_) => _,
    camel: (_, c) => c.toUpperCase(),
    snake: (_, c) => `_${c}`,
    kebab: (_, c) => `-${c}`,
    smoosh: (_, c) => c.toLowerCase(),
  };
  const root = document.createElement("div");
  root.setAttribute(
    "style",
    `position: fixed; top: 0; left: 0; z-index: 9999;`
  );
  for (const mode in modes) {
    const btn = document.createElement("button");
    btn.onclick = () => {
      activeMode = mode;
      replaceText();
    };
    btn.textContent = mode;
    root.appendChild(btn);
  }

  document.body.appendChild(root);
  const observer = new MutationObserver(replaceText);

  function replaceText() {
    observer.disconnect();
    const walker = document.createTreeWalker(
      document.body,
      NodeFilter.SHOW_TEXT
    );
    while (walker.nextNode()) {
      walker.currentNode.data = (walker.currentNode.__data__ ||=
        walker.currentNode.data).replace(
        /(?<=[a-z])[ ]+([a-z])/gi,
        modes[activeMode]
      );
    }
    observer.observe(document.body, {
      subtree: true,
      childList: true,
      characterData: true,
    });
  }
})();