👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-22

javascript react arrays JavaScript

I'm experimenting with I've searched everywhere and can't find a clear answer. I'm currently working on a project using React (v17.0) and I'm trying to destructure elements from a nested array while mapping through it. The objective is to extract specific properties from each object inside an array of arrays. However, I'm working with an scenario where the destructuring leads to `undefined` values for some properties, which results in my component rendering incorrectly. Here's a simplified version of what I have: ```javascript const data = [ [ { id: 1, name: 'Alice' }, { id: 2, name: 'Bob' } ], [ { id: 3, name: 'Charlie' }, { id: 4, name: 'David' } ] ]; const App = () => { return ( <div> {data.map((subArray) => ( <div key={subArray[0].id}> {subArray.map(({ id, name }) => ( <p key={id}>{name}</p> ))} </div> ))} </div> ); }; ``` I expected each name to render correctly from each nested array. However, I'm getting a React warning about `key` props indicating that keys might not be unique. I'm also seeing that when I click on the names in the UI, it occasionally throws an behavior saying `TypeError: want to read properties of undefined (reading 'id')`. I suspect this has to do with how I'm destructuring the `subArray` and the potential for there being an empty nested array or accessing an index that does not exist. What is the best practice to handle this scenario to ensure that all keys are unique and that I avoid the `TypeError`? Any insights or best practices would be highly appreciated! I'm on Ubuntu 20.04 using the latest version of Javascript. Any feedback is welcome! For context: I'm using Javascript on macOS. Thanks in advance!