Alpha-numeric sub-list number generator in TypeScript

sub-list-number.ts

/**
	The function takes care of numbering a sub-list with an arbitrary number of entries.
	
	@param rowNumber The number of the entry in the main list. This will be prepended to the lettering.

	Usage example:

	```
	const list = [['foo', 'bar'], ['bar', 'baz', 'foo']];

	list.forEach((sub, i) => {
		const generator = subListNumberGenerator(i + 1);
		sub.forEach(() => console.log(generator.next().value));
	});
	```

	The output is in the following format *(given that `rowNumber` is `1`)*:
	- 1.a.
	- 1.b.
	
		...
	- 1.aa.
	- 1.ab.

		...
	- 1.az.
	- 1.ba.
*/
function* subListNumberGenerator(rowNumber: number, separator = '.'): Generator<string, string, string> {
	const letters = [ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z' ];
	const l = letters.length;
	const iterations = [0];

	while (true) {
		const letter = iterations
			.map((i) => letters[i])
			.toString()
			.replace(/,/g, '');
		let i = iterations.length - 1;
		iterations[i]++;
		if (iterations[i] === l) {
			if (iterations.every((value) => value === l || value === l - 1)) iterations.push(0);
			while (iterations[i] >= l) {
				iterations[i--] = 0;
				if (i >= 0) iterations[i]++;
			}
			if (iterations[0] === l) iterations[0] = 0;
		}

		yield rowNumber + separator + letter + separator;
	}
}