👀 Views: 2 💬 Answers: 1 📅 Created: 2025-06-06

merge-sort javascript arrays JavaScript

I'm sure I'm missing something obvious here, but I'm testing a new approach and I'm working on a project and hit a roadblock. I'm currently implementing a Merge Sort algorithm in JavaScript, but I'm encountering an unexpected behavior where my original array seems to be altered during the sort process. I've followed a typical recursive approach, but despite using separate arrays for the merging step, the original array's content appears to change. Here’s the code I wrote: ```javascript function mergeSort(arr) { if (arr.length <= 1) return arr; const mid = Math.floor(arr.length / 2); const left = mergeSort(arr.slice(0, mid)); const right = mergeSort(arr.slice(mid)); return merge(left, right); } function merge(left, right) { let result = [], i = 0, j = 0; while (i < left.length && j < right.length) { if (left[i] < right[j]) { result.push(left[i]); i++; } else { result.push(right[j]); j++; } } return result.concat(left.slice(i)).concat(right.slice(j)); } const unsortedArray = [3, 1, 4, 1, 5, 9, 2, 6]; const sortedArray = mergeSort(unsortedArray); console.log(sortedArray); // [1, 1, 2, 3, 4, 5, 6, 9] console.log(unsortedArray); // Expected: [3, 1, 4, 1, 5, 9, 2, 6] ``` However, when I run this code, the output for `unsortedArray` is not what I expect; it seems to be modified after the sort. I've verified that I'm using `slice` on the original array, which should create a shallow copy. Could there be something I'm missing in how JavaScript handles arrays or references? I've also tried creating a deep copy using `JSON.parse(JSON.stringify(arr))`, but that approach feels inefficient for larger arrays. Any insights would be appreciated! For context: I'm using Javascript on macOS. Am I missing something obvious? Thanks for your help in advance! Any ideas how to fix this? This issue appeared after updating to Javascript 3.11. I'm working in a CentOS environment. What's the best practice here?