Get element(s) by xpath

getElementByXPath.mjs

/**
  * Get an element by XPath.
  * Includes workaround for browser bug not allowing SVG elements to be selected; use the virtual "_" prefix to reference the context node's namespace.
  * @param {string} expression - A string representing the XPath to be evaluated.
  * @param {Node|Document} [contextNode] - The context node.
  * @param {XPathEvaluator|Document} [document] - The document via which evaluate() will be called. Defaults to the context node's document, if specified; otherwise globalThis.document. Required if context node and globalThis.document are both absent.
  * @param {boolean} [ordered=true] - Whether to return the "first" node selected by the expression. If false, allows the XPath engine to return an arbitrary node selected by the expression.
  * @returns {?Node}
  */
export function getElementByXPath(expression, contextNode, document, ordered=true) {
	if (document === undefined) document = (contextNode ? contextNode.getRootNode() : globalThis.document); // TypeError if bad parameters
	if (contextNode === undefined) contextNode = document;

	var result = document.evaluate(
		expression,
		contextNode,
		(prefix) => (prefix === '_' ? contextNode.namespaceURI : document.lookupNamespaceURI(prefix)),
		ordered ? XPathResult.FIRST_ORDERED_NODE_TYPE : XPathResult.ANY_UNORDERED_NODE_TYPE
	);
	return result.singleNodeValue || null;
}


/**
  * Get multiple elements by XPath.
  * Includes workaround for browser bug not allowing SVG elements to be selected; use the virtual "_" prefix to reference the context node's namespace.
  * @param {string} expression - A string representing the XPath to be evaluated.
  * @param {Node|Document} [contextNode] - The context node.
  * @param {XPathEvaluator|Document} [document] - The document via which evaluate() will be called. Defaults to the context node's document, if specified; otherwise globalThis.document. Required if context node and globalThis.document are both absent.
  * @param {boolean} [ordered=true] - Whether to return the nodes in strict order. If false, allows the XPath engine to return the elements in arbitrary order.
  * @param {boolean} [snapshot=true] - If true, immediately return an Array containing all selected elements; if false, return a "lazy" Iterator yielding all selected elements.
  * @returns {Array.<Node>|Iterable.<Node>}
  */
export function getElementsByXPath(expression, contextNode, document, ordered=true, snapshot=true) {
	if (document === undefined) document = (contextNode ? contextNode.getRootNode() : globalThis.document); // TypeError if bad parameters
	if (contextNode === undefined) contextNode = document;

	var result = document.evaluate(
		expression,
		contextNode,
		(prefix) => (prefix === '_' ? contextNode.namespaceURI : document.lookupNamespaceURI(prefix)),
		snapshot ? (ordered ? XPathResult.ORDERED_NODE_SNAPSHOT_TYPE : XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE)
		         : (ordered ? XPathResult.ORDERED_NODE_ITERATOR_TYPE : XPathResult.UNORDERED_NODE_ITERATOR_TYPE)
	);
	return xpathresultToNativeType(result);
}


/**
  * @param {string} expression
  * @param {Node|Document} [contextNode]
  * @param {XPathEvaluator|Document} [document]
  * @param {number} [resultType]
  * @returns {?Node|Array.<Node>|Iterable.<Node>|?number|?string|?boolean}
  */
export function getByXPath(expression, contextNode, document, resultType=XPathResult.ANY_TYPE) {
	if (document === undefined) document = (contextNode ? contextNode.getRootNode() : globalThis.document); // TypeError if bad parameters
	if (contextNode === undefined) contextNode = document;

	var result = document.evaluate(
		expression,
		contextNode,
		(prefix) => (prefix === '_' ? contextNode.namespaceURI : document.lookupNamespaceURI(prefix)),
		resultType
	);
	return xpathresultToNativeType(result);
}


/**
  * Convert any XPathResult object into its corresponding Javascript object.
  * @param {XPathResult} result
  * @returns {?Node|Array.<Node>|Iterable.<Node>|?number|?string|?boolean}
  */
export function xpathresultToNativeType(result) {
	switch (result.resultType) {
		case XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE:
		case XPathResult.ORDERED_NODE_SNAPSHOT_TYPE:
			// XPath Snapshot, as JS Array
			return Array.from(
				// TODO benchmark further
				{ length: result.snapshotLength },
				(_0, i) => result.snapshotItem(i)
			);

		case XPathResult.UNORDERED_NODE_ITERATOR_TYPE:
		case XPathResult.ORDERED_NODE_ITERATOR_TYPE:
			// XPath Iterator, as JS Generator
			return (function* (xp_it) {
				// TODO benchmark
				for (
					var value = xp_it.iterateNext() ;
					value !== null ;
					value = xp_it.iterateNext()
				) {
					yield value;
				}
			})(result);

		case XPathResult.ANY_UNORDERED_NODE_TYPE:
		case XPathResult.FIRST_ORDERED_NODE_TYPE:
			// Single node value
			return result.singleNodeValue || null;

		case XPathResult.NUMBER_TYPE:
			return result.numberValue ?? null;

		case XPathResult.STRING_TYPE:
			return result.stringValue ?? null;

		case XPathResult.BOOLEAN_TYPE:
			return result.booleanValue ?? null;

		default:
			throw new DOMException(`Unsupported XPathResult type: ${result.resultType}`, 'NotSupportedError');
	}
}

TODO maybe benchmark the billion different ways one could call Array.from