Adding elements to array by keys JavaScript

Elements in an array don't need to be added immediately at the time of declaring this array. You can first declare this array, and then add the necessary elements to it, like this:

javascriptlet arr = [];

arr[0] = 'a';
arr[1] = 'b';
arr[2] = 'c';

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

You can also add elements to an array already filled with data:

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

arr[3] = 'd';
console.log(arr); // shows ['a', 'b', 'c', 'd']

javascriptlet arr = [1, 2, 3];