Function compareSelect

lib/util/comparators.js:477–502

(getter, comparator)

 * @returns {Comparator<T>} comparator
 */
const compareSelect = (getter, comparator) => {
	const cacheEntry = compareSelectCache.get(getter, comparator);
	if (cacheEntry !== undefined) return cacheEntry;
	/**
	 * Returns compare result.
	 * @param {T} a first value
	 * @param {T} b second value
	 * @returns {-1 | 0 | 1} compare result
	 */
	const result = (a, b) => {
		const aValue = getter(a);
		const bValue = getter(b);
		if (aValue !== undefined && aValue !== null) {
			if (bValue !== undefined && bValue !== null) {
				return comparator(aValue, bValue);
			}
			return -1;
		}
		if (bValue !== undefined && bValue !== null) {
			return 1;
		}
		return 0;
	};
	compareSelectCache.set(getter, comparator, result);
	return result;
};

/** @type {WeakMap<Comparator<EXPECTED_ANY>, Comparator<Iterable<EXPECTED_ANY>>>} */
const compareIteratorsCache = new WeakMap();