Coding Challenge

This challenge focuses on how the JavaScript reverse() method works and how it affects the original array due to mutation.

Task

Review the code below and determine what the output will be. Pay close attention to how reversing an array affects references and copies.

Formula

reverse() mutates the original array. Spread syntax creates a new copy.

Example Code


// Reverse an array
const nums = [1, 2, 3, 4];

// reverse() mutates the original array and also returns a reference to it
const r1 = nums.reverse();      // in-place reverse
const r2 = nums;                // same reference as nums after reverse
const r3 = [...nums].reverse(); // reversed copy from the current state

console.log('r1:', r1);
console.log('nums:', nums);
console.log('r3:', r3);

Question

Which of the following matches the output?

Options

r1: [4, 3, 2, 1] • nums: [4, 3, 2, 1] • r3: [1, 2, 3, 4]
r1: [4, 3, 2, 1] • nums: [1, 2, 3, 4] • r3: [4, 3, 2, 1]
r1: [1, 2, 3, 4] • nums: [4, 3, 2, 1] • r3: [4, 3, 2, 1]
r1: [1, 2, 3, 4] • nums: [1, 2, 3, 4] • r3: [1, 2, 3, 4]

Hint: Does reverse() create a new array or modify the original one?