The JavaScript ecosystem in a nutshell. Asked to solve a basic algorithmic problem? Just install a package for it. Why reinvent the wheel when someone's already published is-prime to npm with 47 dependencies, half of which are deprecated? The interviewer's face says it all—equal parts confusion, disbelief, and grudging respect for the audacity. Because let's be real, in production you'd probably use a library too. But maybe, just maybe, you should know how to check if a number is divisible by anything other than 1 and itself without reaching for your package manager.