getFocusableChildren.js

const FOCUSABLE_ELEMENTS = `
	[contenteditable]:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"]),
	[tabindex]:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"])
	a[href]:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"]),
	area[href]:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"]),
	audio:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"]),
	button:not([disabled]):not([inert]):not([aria-hidden="true"]),
	iframe:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"]),
	input:not([disabled]):not([inert]):not([aria-hidden="true"]),
	select:not([disabled]):not([inert]):not([aria-hidden="true"]),
	textarea:not([disabled]):not([inert]):not([aria-hidden="true"]),
	video:not([tabindex^="-"]):not([inert]):not([aria-hidden="true"])`;

function _isNodeHidden(node) {
	if (node.getClientRects().length === 0) {
		return true;
	} else {
		return window.getComputedStyle(node).visibility === "hidden";
	}
}

function getFocusableChildren(node) {
	const elems = node.querySelectorAll(FOCUSABLE_ELEMENTS);
	const focusableChildren = [];
	const len = elems.length;

	let elem;
	let i;
	
	for (i = 0; i < len; i++) {
		elem = elems[i];
		if (!_isNodeHidden(el)) {
			focusableChildren.push(el);
		}
	}
	
	return focusableChildren;
}