fontoxpath/src/selectors/util/concatSequences.js

A minimalistic XPath 3.1 engine in JavaScript

import Sequence from '../dataTypes/Sequence';
import { DONE_TOKEN } from './iterators';
export default function concatSequences (sequences) {
	let i = 0;
	let iterator = null;
	return new Sequence({
		next: () => {
			while (i < sequences.length) {
				if (!iterator) {
					iterator = sequences[i].value();
				}
				const value = iterator.next();
				if (value.done) {
					i++;
					iterator = null;
					continue;
				}
				return value;
			}
			return DONE_TOKEN;
		}
	});
}