👀 Views: 81 💬 Answers: 1 📅 Created: 2025-06-13

javascript arrays reduce flatten JavaScript

I'm prototyping a solution and I'm deploying to production and I'm attempting to set up I'm stuck on something that should probably be simple..... I've searched everywhere and can't find a clear answer. I've looked through the documentation and I'm still confused about I'm trying to flatten a sparse array in JavaScript using `Array.reduce()`, but I'm working with unexpected behavior when handling `undefined` values. My input array can contain nested arrays as well as `undefined` values, and I want to ensure that the final output only contains defined values. Here’s my implementation: ```javascript const flattenArray = (arr) => { return arr.reduce((acc, val) => { if (Array.isArray(val)) { acc.push(...flattenArray(val)); } else if (val !== undefined) { acc.push(val); } return acc; }, []); }; const input = [1, [2, undefined, [3, undefined]], undefined, 4]; const result = flattenArray(input); console.log(result); ``` When I run this code, I expect the output to be `[1, 2, 3, 4]`, but instead, I get `[1, 2, 3, 4, undefined]`. I’ve tried adding additional checks, but I still see `undefined` in the output. Could someone guide to understand what's going wrong here? I've also tried using `Array.flat()` with a depth argument, but that doesn't account for the `undefined` values either. I'm currently using Node.js v14.17.0. Any insights on how to properly flatten the array while ignoring `undefined` values would be greatly appreciated! I'm working on a application that needs to handle this. I'm working on a web app that needs to handle this. How would you solve this? This is part of a larger microservice I'm building. Any suggestions would be helpful. My development environment is macOS. This is my first time working with Javascript stable.