How to structure javascript for Drupal.md.txt

You need to start with:
```js
((Drupal) => {
  Drupal.behaviors.nameOfLibrary = {
    attach(context) {
```

Then it ends with:
```js
    },
  };
})(Drupal);
```

And your custom code goes in the middle. Here's an example:
```js
((Drupal) => {
  Drupal.behaviors.railToggle = {
    attach(context) {
      context
        .querySelectorAll(".rail .component .rail-toggle")
        .forEach((element) => {
          let selector = element.getAttribute("aria-controls");
          let parent = element.parentElement;
          let target = element.parentElement.querySelector(`.${selector}`);
          
          target.setAttribute("aria-hidden", "true");
          parent.setAttribute("aria-expanded", "false");

          element.addEventListener("click", (event) => {
            event.preventDefault();
            target.setAttribute(
              "aria-hidden",
              target.getAttribute("aria-hidden") === "true" ? "false" : "true"
            );
            parent.setAttribute(
              "aria-expanded",
              parent.getAttribute("aria-expanded") === "false"
                ? "true"
                : "false"
            );
          });
        });
    },
  };
})(Drupal);

```