Answer 1

Read the reference about destructuring assignment

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

let a, b, c = 4, d = 8;

[ a, b = 6 ] = [ 2 ];

<a> gets it value from right hand side array [ 2 ]
<b> gets its value from default value that was specified in left hand side array.

* Read the "Default value" section in the above link

[ c, d ] = [ d, c ];

Value of <c> and <d> are swapped.

* Read the "Swapping variables" section in the above link

Answer 2

No problem, it's a good query 👍