Flattening nested arrays is crucial when working with hierarchical data structures, processing API responses with nested arrays, or simplifying complex data for easier manipulation in JavaScript applications. With over 25 years of experience in software development and as the creator of CoreUI, I’ve implemented array flattening in components like tree navigation, nested menu systems, and data aggregation features where multi-level arrays need to be converted into flat structures. From my extensive expertise, the most modern and efficient solution is using the ES2019 flat() method, which handles nested arrays elegantly. This approach is clean, intuitive, and provides excellent control over the flattening depth.