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You have a UserService that needs a Database. Your OrderService needs UserService, Database, and a PaymentGateway. Your NotificationService needs EmailClient and UserService.

One call with the wrong argument type, made once, makes the next 100 million integer additions roughly 3x slower. Hidden classes, inline caches, the tier-up thresholds and every deopt reason — checked against what Node 22 actually does, not what the blog posts say.

You've read "Node.js is single-threaded and non-blocking." Fine. But that sentence raises more questions than it answers. If it's single-threaded, who's doing the file I/O while your JavaScript runs?

You've probably seen gRPC described as "REST but faster." That framing is technically true and practically useless.

EJS, Handlebars, Pug and Nunjucks all do the same three things: tokenize, parse, compile. Build a real one — loops, conditionals, partials, escaping by default — and see exactly where HTML escaping stops protecting you.