LitElement.ready( requireEntireDomTreeReady = false )

ExtendedLitElement.js

class ExtendedLitElement extends LitElement {
	
	static getDuckTypedDescendants(parent, qualifyingPropertyName, stopTraversalOnMatch = true) {

		const descendants = [];

		/**
		 * Use a depth-first search (DFS) algorithm to traverse the DOM tree
		 * @param {Node} node
		 */
		const traverse = node => {

			if( node !== parent && qualifyingPropertyName in node ) {

				descendants.push(node);
				if( stopTraversalOnMatch ) return;  // Stop the traversal when a custom element node is encountered

			}

			for( const childNode of node.childNodes ) {

				traverse(childNode);

			}

		};

		traverse(parent);

		return descendants;

	}

	async ready( requireEntireDomTreeReady = false ) {

		const thisUpdateComplete = await this.updateComplete;

		if( !requireEntireDomTreeReady ) return thisUpdateComplete;

		const descendantsUpdateComplete = await Promise.all(
			Array.from(
				ExtendedLitElement.getDuckTypedDescendants(this, 'updateComplete'),
				node => typeof node.ready === 'function' ? node.ready(true) : node.updateComplete
			).filter(x => !!x)
		);

		return thisUpdateComplete && descendantsUpdateComplete.every(x => !!x);

	}

}