Toggle aria-expanded with ES6 Javascript

I am trying to toggle an aria tag between true and false when a button is clicked. I’ve tried several implementations which seems to do absolutely nothing. Below is what I am currently using which successfully toggles the class. How can I extend this to toggle the aria-expanded value between true and false? Be easy on me, I am transitioning from jQuery to ES6.

const theTrigger = document.getElementById('mobile-form-control');
const theForm = document.querySelectorAll('.l-header__mobile-form');

theTrigger.onclick = function () {
  for (const x of theForm) {
    x.classList.toggle('show');
  }
};

>Solution :

You can toggle the attribute by comparing its value with 'true'.

x.ariaExpanded = x.ariaExpanded !== 'true';