Event Loop
A programming pattern that waits for and dispatches events in a single thread. Node.js uses it to handle thousands of concurrent connections without creating a thread per connection.
What is Event Loop?
A programming pattern that waits for and dispatches events in a single thread. Node.js uses it to handle thousands of concurrent connections without creating a thread per connection.
Event Loop is a foundational concept that sits in the Core Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Event Loop" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
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Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
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Related glossary terms you might want to look up next.
Asynchronous
A communication model where the caller fires off a request and continues without waiting for a response. Essential for non-blocking I/O and event-driven systems.
Throughput
The number of operations a system can handle per unit of time. Think of it as how many cars a highway can move per hour.
Latency
The time delay between sending a request and getting a response. Amazon found every 100ms of extra latency costs 1% in sales.