How do closures retain memory in JavaScript, why can a single shared scope object keep large data alive unexpectedly, and how do you diagnose closure-driven leaks in heap snapshots?

Imagine a backpack that keeps a toy inside even after you leave the playground. Closures are like that backpack—they hold onto variables from their original function. Sometimes the backpack is too big and keeps heavy toys (data) that you don't need anymore, making your room messy.