The ariaModal property of the Element interface reflects the value of the aria-modal attribute, which indicates whether an element is modal when displayed. Applying the aria-modal property to an element with role="dialog" replaces the technique of using aria-hidden on the background for informing assistive technologies that content outside a dialog is inert.
 
A string with one of the following values:
  "true"  -  
The element is modal.
   "false"  -  
The element is not modal.
   
 
In this example the aria-modal attribute on the element with an ID of address-modal is set to "true" indicating that this is a modal dialog. Using ariaModal we update the value to "false".
 
<div
  role="dialog"
  id="address-modal"
  aria-labelledby="dialog1Title"
  aria-describedby="dialog1Desc"
  aria-modal="true"></div>
  
let el = document.getElementById("address-modal");
console.log(el.ariaModal); 
el.ariaModal = "false";
console.log(el.ariaModal);