JavaScript allows us to rotate an array to the left by k steps. One can give an input array to rotate it in the left direction by giving k steps. Let’s see an example to understand the problem.

Example:

Input 
array = [ 1 , 2 , 3 , 4 , 5]  
  k = 3

Output
array = [ 4, 5 , 1, 2 , 3]

There are several approaches to Rotate an array to the left by k steps using JavaScript which are as follows:

Using Temp Array and copy

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array. Now we Copy the first k elements into the temp array. Shift n-k elements from last by k positions to the left. Copy the elements from the temp array into the main array. Return the modified array.

Example: To demonstrate Rotation of an array to the left by k steps using Temp Array and copy.

function rotateLeft(arr, k) {
    const n = arr.length;
    k %= n;


    const temp = arr.slice(0, k);

    // Shift n-k elements from last by k positions to the left
    for (let i = k; i < n; i++) {
        arr[i - k] = arr[i];
    }

    //  Copy the elements 
    for (let i = 0; i < k; i++) {
        arr[n - k + i] = temp[i];
    }

    return arr;
}


const array = [1, 2, 3, 4, 5];
const k = 2;
console.log("rotated array is ", rotateLeft(array, k));

rotated array is  [ 4, 5, 1, 2, 3 ]

Time complexity : O(n)

Space complexity : O(k)

Using Array Splice and Push

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array then splice is used to remove the first k elements from the array, which are then pushed to the end using push method. which then return the modified array.

Example: To demonstrate Rotation of an array to the left by k steps using array splice and push.

function rotateLeft(arr, k) {
    k %= arr.length;
    // To handle cases where k > array length
    arr.push(...arr.splice(0, k));
    return arr;
}


let array = [1, 2, 3, 4, 5];
let k = 3;
console.log("rotated array is", rotateLeft(array, k));

rotated array is [ 4, 5, 1, 2, 3 ]

Time complexity : O(n)

Space complexity : O(n)

Using Slice and Concatenation

To handle the case when k is greater than length of array , we will calculate k modulo the length of the array then slice is used to extract the elements from index k to the end of the array and concatenate them using concat() with the elements from the beginning of the array to index k returning the result.

Example: To demonstrate Rotation of an array to the left by k steps using Slice and concatenation.

function rotateLeft(arr, k) {
    k %= arr
        .length;
    return arr
        .slice(k)
        .concat(arr.slice(0, k));
}


let array = [1, 2, 3, 4, 5];
let k = 3;
console.log("rotated array is : ", rotateLeft(array, k));

rotated array is :  [ 4, 5, 1, 2, 3 ]

Time complexity : O(n)

Space complexity : O(n)