getNestedArraysMaxLength.js

function getNestedArraysMaxLength(inputArray) {
	let maxLength = -Infinity;

	inputArray.forEach((value, index) => {
		const seriesLength = findSeriesLength(inputArray, index);
		maxLength = Math.max(maxLength, seriesLength);
	});

	return maxLength;
}

function findSeriesLength(arr, nextIndex) {
	let count = 0;

	while (true) {

		let nextValue = arr[nextIndex];

		if (nextValue === null) {
			return count;
		}

		arr[nextIndex] = null;
		nextIndex = nextValue;

		count++;
	}
}