How to get the length of all non-nested items in nested arrays?

Question

The .length property on an array will return the number of elements in the array. For example, the array below contains 2 elements:

[1, [2, 3]] // 2 elements, number 1 and array [2, 3] Suppose we instead wanted to know the total number of non-nested items in the nested array. In the above case, [1, [2, 3]] contains 3 non-nested items, 1, 2 and 3.

Examples

getLength([1, [2, 3]]) ➞ 3
getLength([1, [2, [3, 4]]]) ➞ 4
getLength([1, [2, [3, [4, [5, 6]]]]]) ➞ 6

Answer 1

You can flatten the array using .flat(Infinity) and then get the length. Using .flat() with an argument of Infinity will concatenate all the elements from the nested array into the one outer array, allowing you to count the number of elements:

const getLength = arr => arr.flat(Infinity).length;

console.log(getLength([1, [2, 3]])) // ➞ 3
console.log(getLength([1, [2, [3, 4]]])) // ➞ 4
console.log(getLength([1, [2, [3, [4, [5, 6]]]]])) // ➞ 6