Multidimensional arrays in JavaScript

Array elements can be not only strings and numbers, but also arrays. In this case, we get an array of arrays, or a multidimensional array.

In the following example, the array arr consists of three elements, which in turn are arrays:

let arr = [['a', 'b', 'c'], ['d', 'e', 'f'], ['g', 'h', 'i']];

Let's rewrite in a more understandable way:

let arr = [
	['a', 'b', 'c'],
	['d', 'e', 'f'],
	['g', 'h', 'i'],
];

Depending on the level of nesting, arrays can be two-dimensional - an array of arrays, three-dimensional - an array of arrays of arrays (and so on - four-dimensional, five-dimensional, etc.).

The above array is two-dimensional, since there are other sub-arrays inside one array, and there are no other arrays already in these sub-arrays.

To display any element from a two-dimensional array, you should write not one pair of square brackets, but two:

let arr = [
	['a', 'b', 'c'],
	['d', 'e', 'f'],
	['g', 'h', 'i'],
];

console.log(arr[0][1]); // shows 'b'
console.log(arr[1][2]); // shows 'f'

Given the following array:

let arr = [
	['a', 'b', 'c'],
	['d', 'e', 'f'],
	['g', 'h', 'i'],
	['j', 'k', 'l'],
];

Use it to output elements with the text 'l', 'e', 'g' and 'a'

Given the following array:

let arr = [[1, 2], [3, 4], [5, 6]];

Referring to each array element, find the sum of all its elements.