Reverse an Array in JavaScript

1// Method 1: Using reverse() method (mutates original)
2let arr1 = [1, 2, 3, 4, 5];
3arr1.reverse();
4console.log("Using reverse():", arr1);
5
6// Method 2: Using reverse() without mutation (spread operator)
7let arr2 = [1, 2, 3, 4, 5];
8let reversed = [...arr2].reverse();
9console.log("\nOriginal:", arr2);
10console.log("Reversed (new array):", reversed);
11
12// Method 3: Using for loop
13function reverseArray(arr) {
14    let reversed = [];
15    for (let i = arr.length - 1; i >= 0; i--) {
16        reversed.push(arr[i]);
17    }
18    return reversed;
19}
20
21console.log("\nUsing loop:", reverseArray([10, 20, 30, 40]));
22
23// Method 4: Using while loop with two pointers
24function reverseArrayTwoPointers(arr) {
25    let left = 0;
26    let right = arr.length - 1;
27    let reversed = [...arr];
28    
29    while (left < right) {
30        // Swap elements
31        [reversed[left], reversed[right]] = [reversed[right], reversed[left]];
32        left++;
33        right--;
34    }
35    return reversed;
36}
37
38console.log("\nTwo pointers:", reverseArrayTwoPointers([1, 2, 3, 4, 5]));
39
40// Method 5: Using reduce
41function reverseArrayReduce(arr) {
42    return arr.reduce((acc, item) => [item, ...acc], []);
43}
44
45console.log("\nUsing reduce:", reverseArrayReduce(['a', 'b', 'c', 'd']));
46
47// Method 6: In-place reversal (mutates original)
48function reverseInPlace(arr) {
49    let left = 0;
50    let right = arr.length - 1;
51    
52    while (left < right) {
53        [arr[left], arr[right]] = [arr[right], arr[left]];
54        left++;
55        right--;
56    }
57    return arr;
58}
59
60let original = [1, 2, 3, 4];
61console.log("\nIn-place:", reverseInPlace(original));
62console.log("Original mutated:", original);