Best practice

found alert() call; should this be in production code?

found debugger call; should this be in production code?

found confirm() call; should this be in production code?

found prompt() call; should this be in production code?

Creating and using a large number of zlib objects simultaneously can cause significant memory fragmentation. It is strongly recommended that the results of compression operations be cached or made synchronous to avoid duplication of effort.

undefined is not a reserved keyword in Javascript, so this is “valid” Javascript but highly confusing and likely to result in bugs.

Lazy loading can complicate code bundling if care is not taken, also requires are run synchronously by Node.js. If they are called from within a function, it may block other requests from being handled at a more critical time. The best practice is to require modules at the beginning of each file, before and outside of any functions.