axe-core/lib/checks/shared/duplicate-id.js

Accessibility engine for automated Web UI testing

const id = node.getAttribute('id').trim();
// Since empty ID's are not meaningful and are ignored by Edge, we'll
// let those pass.
if (!id) {
	return true;
}
const root = axe.commons.dom.getRootNode(node);
const matchingNodes = Array.from(root.querySelectorAll(
	`[id="${ axe.commons.utils.escapeSelector(id) }"]`
)).filter(foundNode => foundNode !== node);

if (matchingNodes.length) {
	this.relatedNodes(matchingNodes);
}
this.data(id);

return (matchingNodes.length === 0);