AI solution for JavaScript Quiz on BFE.dev
90. array keys

The code outputs the following:

["length"]
["0", "length"]
["0", "2", "length"]
["0", "2", "length"]

Explanation:

• Reflect.ownKeys([]) returns an array containing only the "length" property, because the array is empty.
• Reflect.ownKeys([,]) returns an array containing "0" and "length", because the array has one element but with an empty slot (trailing comma notation).
• Reflect.ownKeys([1,,2]) returns an array containing "0", "2", and "length", because the array has 3 elements, but the middle one is empty (comma notation).
• Reflect.ownKeys([...[1,,2]]) first creates a new array [1,,2] with an empty slot, then uses the spread operator to create a new array with the same elements. The resulting array has the same keys as the previous case.