MarkLogic’s cts.frequency function is magic. Could we do something more explicit? (Spoiler: probably not by much)

values.js

// https://github.com/jmakeig/iterant/issues/30
function head(itr) {
	if (itr[Symbol.iterator]) return itr[Symbol.iterator]().next().value;
}

function* values(ref, options) {
	const sequence = cts.values(ref, options);
	for (const value of sequence) {
		yield {
			value: value.valueOf(),
			// Lazily call cts.frequency()
			get frequency() {
				return cts.frequency(value);
			},
			// Used in default coercion 
			//   https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/valueOf
			valueOf() {
				return value.valueOf();
			}
		};
	}
}

// Usage: 
//   const { value, frequency } = head(values(tag));