How Does Node.js\'s Event Loop Manage Asynchronous Operations?

Understanding the Event Loop

Q1: If the application is single-threaded, how are timeouts processed while the JS engine accepts and executes requests?

A: Node manages the event loop mechanism through multiple threads, including IO threads, despite running on a single thread. Node monitors the OS for completed IO operations, and when it detects completed network requests or filesystem calls, it adds them to a queue for execution.

Q2: What executes these setTimeout functions behind the scenes?

A: The event loop is responsible for scheduling and executing the callback functions associated with setTimeout calls. It doesn't run JavaScript in the background; rather, it maintains a queue of JavaScript functions to execute when the OS indicates that IO operations are complete.

Q3: How does the JS engine recognize asynchronous functions for placement in the event loop?

A: Node has a predetermined set of async functions that make system calls. When these functions are invoked, Node identifies them as asynchronous and queues their callback functions for execution in the event loop.

Q4: Why do some sources claim that the event loop processes the code after an async function has executed?

A: This statement can be misleading. While the event loop doesn't start processing until the code following an async function has been executed, it immediately adds the callback function to its queue. Typically, the code after an async function does not perform significant work, leading to the impression that the event loop only starts after its execution.

Q5: Is there an "async" keyword or similar mechanism in JS like C# to indicate asynchronous methods?

A: No, JavaScript does not have an explicit "async" keyword or attribute. Node identifies asynchronous functions based on their use of predefined system-call functions.

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