Merging arrays is essential when combining data from multiple sources, concatenating user selections, or building unified datasets in JavaScript applications. With over 25 years of experience in software development and as the creator of CoreUI, I’ve implemented array merging extensively in components like multi-select filters, data aggregation systems, and navigation builders where multiple arrays need to be combined. From my extensive expertise, the most modern and efficient solution is using the ES6 spread operator, which creates a new array without mutating the original arrays. This approach is clean, readable, and performs well for most use cases.