Sparse arrays in JavaScript

If there are gaps in the sequence of keys in the array, then you can get a sparse array. Let's see what it looks like. Let's have some array:

let arr = ['a', 'b', 'c'];

Let's add one more element to this array so that the sequence of keys have gaps:

arr[4] = '!';

As a result, a "hole", which has the value undefined, appears in the array:

console.log(arr); // shows ['a', 'b', 'c', undefined, '!']

The length of the array will consider all holes. That is, in our case, it will be 5, and not 4:

console.log(arr.length); // shows 5

Find out the length of the next array:

let arr = [];

arr[3] = 'a';
arr[8] = 'b';