👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-14

javascript arrays copying JavaScript

I'm refactoring my project and I'm writing unit tests and Quick question that's been bugging me - I've been running into a perplexing issue with shallow copies of nested arrays in JavaScript... I have an array of objects, and when I create a shallow copy of it using the spread operator, I expect the nested objects to remain unchanged when I modify them. However, I'm finding that modifying a property of a nested object in the copied array also affects the original array. Here's a simplified version of what I've tried: ```javascript const originalArray = [ { id: 1, name: 'Alice', scores: [90, 80] }, { id: 2, name: 'Bob', scores: [70, 75] } ]; const copiedArray = [...originalArray]; // Modify a nested score in the copied array copiedArray[0].scores[0] = 95; console.log(originalArray[0].scores[0]); // Output is 95, unexpectedly! ``` I thought that using the spread operator would create a new array with new references for the objects, but it seems like the nested arrays are still referenced from the original objects. I also tried using `Array.prototype.map` to create the copy: ```javascript const newArray = originalArray.map(item => ({ ...item })); ``` But I still see the same mutation issue when modifying nested objects. Am I missing something about how references work in JavaScript when it comes to nested data structures? Is there a best practice to completely clone an array of objects, including their nested properties to avoid this kind of mutation? I'm currently using Node.js v16.13.0, and it's crucial that I preserve the integrity of the original data structure. Any insights would be greatly appreciated! I'm on Windows 11 using the latest version of Javascript. What am I doing wrong?