Get element(s) by xpath

getElementByXPath.js

/**
  * Get an element by XPath.
  * @param {string} expression - A string representing the XPath to be evaluated.
  * @param {Element} [context] - The context node. Defaults to the current document.
  * @param {Document} [document] - The document against which evaluate() will be called. Defaults to the context node's document.
  * @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 {Element|null}
  */
function getElementByXPath(expression, context = null, document = null, ordered = true) {
	if (context === null) context = window.document;
	if (document === null) document = context.getRootNode();
	const result = document.evaluate(
		expression,
		context,
		document,
		ordered ? XPathResult.FIRST_ORDERED_NODE_TYPE : XPathResult.ANY_UNORDERED_NODE_TYPE
	);
	return result.singleNodeValue || null;
}


/**
  * Get multiple elements by XPath.
  * @param {string} expression - A string representing the XPath to be evaluated.
  * @param {Element} [context] - The context node. Defaults to the current document.
  * @param {Document} [document] - The document against which evaluate() will be called. Defaults to the context node's document.
  * @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.<Element>|Iterable.<Element>}
  */
function getElementsByXPath(expression, context = null, document = null, ordered = true, snapshot = true) {
	if (context === null) context = window.document;
	if (document === null) document = context.getRootNode();
	if (snapshot) {
		// Array
		const result = document.evaluate(
			expression,
			context,
			document,
			ordered ? XPathResult.ORDERED_NODE_SNAPSHOT_TYPE : XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE
		);
		return Array.from({
			[Symbol.iterator]() {
				var i = 0;
				return ({
					next() {
						const value = result.snapshotItem(i++);
						return ({ value, done: !value });
					},
				});
			}
		});
	} else {
		// Iterator
		const result = document.evaluate(
			expression,
			context,
			document,
			ordered ? XPathResult.ORDERED_NODE_ITERATOR_TYPE : XPathResult.UNORDERED_NODE_ITERATOR_TYPE
		);
		return ({
			next() {
				const value = result.iterateNext();
				return { value, done: !value };
			},
			[Symbol.iterator]() {
				return this;
			},
		});
	}
}

TODO: compare de performance

// Option 1: status quo
Array.from({
	[Symbol.iterator]() {
		var i = 0;
		return ({
			next() {
				const value = result.snapshotItem(i++);
				return ({ value, done: !value });
			},
		});
	}
});

// Option 2: generator meme
Array.from({
	*[Symbol.iterator]() {
		const length = result.snapshotLength;
		for( var i = 0 ; i < length ; i++ ) {
			yield result.snapshotItem(i);
		}
	}
});

// Option 3: length-and-index meme (deep fried)
Array.from(
	new Proxy(
		result,
		{
			get(t, p, r) {
				if (typeof p === 'string') {
					if (p === 'length')
						return t.snapshotLength;
					if (!isNaN(parseInt(p)))
						return t.snapshotItem(p);
				}
				return Reflect.get(...arguments);
			}
		}
	)
)