Example 6-17. Configuring an iterator with an initial parameter

function* counter(increment) {
	var count = 0;
	increment = increment || 1;
	while (true) {
		count = count + increment;
		increment = (yield count) || increment;
	}
}

var evens = counter(2);
console.log('Even numbers'); // Even numbers
console.log(evens.next().value); // 2
console.log(evens.next().value); // 4
console.log(evens.next().value); // 6

var fives = counter(5);
console.log('Count by fives'); // Count by fives
console.log(fives.next().value); // 5
console.log(fives.next().value); // 10
console.log(fives.next().value); // 15