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Mastering Node.js - Second Edition by Kevin Faaborg, Sandro Pasquali

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Understanding the event loop

The following three points are important to remember, as we break down the event loop:

  • The event loop runs in the same (single) thread your JavaScript code runs in. Blocking the event loop means blocking the entire thread.
  • You don't start and/or stop the event loop. The event loop starts as soon as a process starts, and ends when no further callbacks remain to be performed. The event loop may, therefore, run forever.
  • The event loop delegates many I/O operations to libuv, which manages these operations (using the power of the OS itself, such as thread pools), notifying the event loop when results are available. An easy-to-reason-about single-threaded programming model is reinforced with the efficiency of multithreading. ...

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