The read-only sandbox property of the HTMLIFrameElement returns a live DOMTokenList object indicating extra restrictions on the behavior of the nested content. It reflects the <iframe> element's sandbox content attribute.
A live DOMTokenList object.
Although the sandbox property itself is read-only in the sense that you can't replace the DOMTokenList object, you can still assign to the sandbox property directly, which is equivalent to assigning to its value property. You can also modify the DOMTokenList object using the add(), remove(), replace(), and toggle() methods.
<iframe
id="el"
title="example"
src="https://example.com"
sandbox="allow-same-origin allow-scripts"></iframe>const el = document.getElementById("el");
console.log(Array.from(el.sandbox)); // Output: ["allow-same-origin", "allow-scripts"]
el.sandbox = "";
console.log(Array.from(el.sandbox)); // Output: []