The output is `[2, 4, 6, 8]`. This code demonstrates a common and elegant use of arrow functions as callbacks. The `map()` method creates a new array populated with the results of calling a provided function on every element in the calling array. Here, the arrow function `num => num * 2` takes each element from the `numbers` array and returns its doubled value. The concise syntax of arrow functions makes them particularly well-suited for this kind of operation, eliminating the boilerplate code of a full function expression. This example shows how arrow functions can make functional programming patterns more readable. The original array remains unchanged, and a new array with the transformed values is created and stored in `doubled`. This pattern is frequently used for transforming data in a clean, declarative way without side effects.