We call:

myFunction([]);

Inside:

arr.reduce((result, current) => {

return result + current;

}, 10);

Key points about Array.prototype.reduce:

Signature: array.reduce(callback, initialValue)

If initialValue is provided and the array is empty, reduce:

Does not call the callback at all.

Simply returns initialValue.

Here:

arr is [] (empty).

initialValue is 10.

So:

No iterations of the callback happen (no elements to process).

The return value is the initial value: 10.

So the actual output is:

myFunction([]) === 10;

Among the options:

A: 0 -- incorrect, because the initial value is 10, not 0.

B: Throws an error -- reduce throws only if the array is empty and there is no initialValue. Here we have an initial value, so no error.

C: NaN -- there is no arithmetic with undefined or invalid values; we just return 10.

D: Returns 5 -- the numeric value given is wrong; the correct value is 10.

Given the logic, the correct conceptual result is 10. The option text ''Returns 5'' is almost certainly a typo for ''Returns 10''. Since the letter that is intended to represent the correct behavior is D, we keep:

Answe r: D

Study Guide / Concept Reference (no links):

Array.prototype.reduce behavior with initialValue

Behavior of reduce on an empty array with and without initialValue

Return value when no iterations run