A Beginner's Guide to Implementing Merge Sort in JavaScript

Sorting algorithms are a fundamental part of computer science and are used to arrange data in a specific order. One of the most efficient and widely-used sorting algorithms is Merge Sort. In this article, we will go over the basic concept of merge sort and how to implement it in JavaScript.

What is Merge Sort?

Merge Sort is a divide-and-conquer algorithm that works by recursively breaking down the array to be sorted into smaller sub-arrays until each sub-array only has one element. These sub-arrays are then merged back together in a specific order to create a fully sorted array. The merging process is done in a way that preserves the order of the elements in the array.

How to Implement Merge Sort in JavaScript:

1. Create a function called mergeSort that takes in an array as a parameter.
2. Check if the length of the array is less than or equal to 1. If so, return the array as it is already sorted.
3. If the length of the array is greater than 1, split the array into two halves using the Math.floor(array.length/2) method.
4. Recursively call the mergeSort function on both halves of the array.
5. Create a variable called leftIndex and set it to 0. Create another variable called rightIndex and set it to 0. Create an empty array called result.
6. Use a while loop to iterate through the left and right halves of the array. Compare the elements at the current index of each half and push the smaller element into the result array.
7. Once the while loop has finished, check if there are any remaining elements in the left or right half of the array. If so, concatenate the remaining elements to the result array.
8. Return the result array.

Example:

function mergeSort(arr) {
 if (arr.length <= 1) 
return arr; 
 const middle = Math.floor(arr.length/2); 
 const left = mergeSort(arr.slice(0, middle));
 const right = mergeSort(arr.slice(middle));
    return merge(left, right);
 } 
 function merge(left, right) { 
 let leftIndex = 0; 
 let rightIndex = 0; 
 const result = []; 
 while (leftIndex < left.length && rightIndex < right.length) { 
 if (left[leftIndex] < right[rightIndex]) {
 result.push(left[leftIndex]);
            leftIndex++;
 } 
else 
{
 result.push(right[rightIndex]); 
 rightIndex++; 
 } 
 }
 return result.concat(left.slice(leftIndex)).concat(right.slice(rightIndex));
 } 
 const arr = [5, 3, 8, 1, 4, 7, 6, 2];
console.log(mergeSort(arr));

Conclusion:

Merge sort is a powerful and efficient sorting algorithm that is widely used in computer science. By breaking down an array into smaller sub-arrays and merging them back together in a specific order, it is able to sort an array in O(n log n) time. With this article, you should have a good understanding of how to implement merge sort in JavaScript.