Javascript: getElementByXPath

function getElementByXPath(path, context=null, document=null, namespaceResolver=null, first_ordered=true) {
  if (context === null) context = window.document.documentElement;
  if (document === null) document = context.ownerDocument;
  if (namespaceResolver === null) namespaceResolver = document.createNSResolver(context);
  const result = document.evaluate(
    path,
    context,
    namespaceResolver,
    first_ordered ? XPathResult.FIRST_ORDERED_NODE_TYPE : XPathResult.ANY_UNORDERED_NODE_TYPE,
    null);
  return result.singleNodeValue || null;
}

function getElementsByXPath(path, context=null, document=null, namespaceResolver=null, ordered=true) {
  if (context === null) context = window.document.documentElement;
  if (document === null) document = context.ownerDocument;
  if (namespaceResolver === null) namespaceResolver = document.createNSResolver(context);
  const result = document.evaluate(
    path,
    context,
    namespaceResolver,
    ordered ? XPathResult.ORDERED_NODE_SNAPSHOT_TYPE : XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
    null);
  return Array.from(new Proxy(result, {
    get(target, property, receiver) {
      if (typeof property === "string") {
        if (property === "length") return target.snapshotLength;
        if (!isNaN(property)) return target.snapshotItem(property);
      }
      return Reflect.get(...arguments);
    }
  }));
}

// Alternate possibilities:

function getElementsByXPath(path, context=null, document=null, namespaceResolver=null, ordered=true, snapshot=true) {
  if (context === null) context = window.document.documentElement;
  if (document === null) document = context.ownerDocument;
  if (namespaceResolver === null) namespaceResolver = document.createNSResolver(context);
  if (!snapshot) {
    // Optional codepath to allow streaming iteration
    const result = document.evaluate(
      path,
      context,
      namespaceResolver,
      ordered ? XPathResult.ORDERED_NODE_ITERATOR_TYPE : XPathResult.UNORDERED_NODE_ITERATOR_TYPE,
      null);
    return Object.assign(result, ({
      next() {
        const value = this.iterateNext();
        return { value, done: !value };
      },
      [Symbol.iterator]() {
        return this;
      }
    }));
  }
  const result = document.evaluate(path,
    context,
    namespaceResolver,
    ordered ? XPathResult.ORDERED_NODE_SNAPSHOT_TYPE : XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE,
    null);
  return Array.from(new Proxy(result, {
    get(target, property, receiver) {
      if (typeof property === "string") {
        if (property === "length") return target.snapshotLength;
        if (!isNaN(property)) return target.snapshotItem(property);
      }
      return Reflect.get(...arguments);
  /*
  // TODO compare performance:
  return Array.from(Object.assign(result, {
    [Symbol.iterator]() {
      var i = 0;
      return {
        next() {
          const value = this.snapshotItem(i++);
          return { value, done: !value };
        }
      };
    }
  }));
  */
}