Border elements in JavaScript

Given the following array:

[1, 2, 3]

Display the first element of this array.

Given the following array:

[1, 2, 3]

Display the last element of this array.

Given the following array:

[1, 2, 3]

Add the elements 4, 5, 6 to its end.

Given the following array:

[1, 2, 3]

Add the elements 4, 5, 6 to its start.

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