Arbitrary arrays in JavaScript

Multidimensional arrays do not have to be the same as we discussed above. Look at the following array for example:

let arr = [['a', 'b', [1, 2, 3], [4, 5]], ['d', ['e', 'f']]];

As you can see, this array is "unusual". It contains arrays ([1, 2, 3] and ā… cā†[4, 5]) next to regular elements (for example, 'a', 'b'). Let's rewrite our array in a more understandable way:

let arr = [ [ 'a', 'b', [1, 2, 3], [4, 5], ], [ 'd', ['e', 'f'], ], ];

Given the following array:

let arr = [[1, 2, 3, [4, 5, [6, 7]]], [8, [9, 10]]];

Manually - without a loop, find the sum of this array elements.

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