Explain Event Loop in Node.js

Instruction: Describe the concept of the Event Loop in Node.js and its significance in non-blocking I/O operations.

Context: This question assesses the candidate's understanding of the core mechanism that enables Node.js to perform non-blocking I/O operations - despite JavaScript being single-threaded.

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The event loop coordinates JavaScript callbacks with asynchronous work. Ordinary callbacks on one Node.js event-loop thread run one at a time; Node.js as a whole is not limited to one thread. Network I/O often uses operating-system facilities, while several filesystem and other APIs use libuv's worker pool.

The poll phase processes most I/O callbacks, the check phase runs setImmediate callbacks, and the pending-callback phase handles certain deferred system callbacks...

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