BackendFrontend
Event Loop
Also written as Non-Blocking I/O, Async Runtime
The mechanism that lets single-threaded languages like JavaScript handle many operations at once by never waiting — starting work and processing results as they arrive.
Think of it like
A waiter who takes other tables' orders while the kitchen cooks, rather than standing still until a dish is ready.
Junior or senior?
Junior sounds like
Knows async/await syntax.
Senior sounds like
Can explain what blocking the event loop does to a Node service, having presumably done it once.
Ask them
“What happens to a Node.js service if you do heavy synchronous work in a request handler?”