Turning messy nested arrays into clean, flat ones — and understanding why it matters. At some point, you'll run into an array that looks like this: const data = [ 1 , [ 2 , 3 ], [ 4 , [ 5 , 6 ]], 7 ]; Enter fullscreen mode Exit fullscreen mode Arrays inside arrays. Arrays inside arrays inside arrays. It's like opening a box and finding more boxes inside, and inside those boxes — even more boxes. This is a nested array , and while they show up naturally in real-world data (think category trees, API responses, multi-level menus), they're a pain to work with when you just need a simple, flat list of values. That's where flattening comes in. When I first encountered this concept in the ChaiCode Web Dev Cohort 2026, it seemed like a niche problem. But it kept showing up — in coding challenges, interview questions, and even real project scenarios. Let me walk you through it. What Are Nested Arrays? A nested array is simply an array that contains other arrays as elements.…