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Understanding the nodejs event loop
This document discusses the event loop in Node.js, which allows JavaScript to perform non-blocking I/O operations and asynchronous code. It explains that the event loop handles pending callbacks, timers, and incoming connections in different phases. Common asynchronous functions like setTimeout(), setImmediate(), and process.nextTick() are explained in terms of how they interact with the event loop. Finally, some common misconceptions about the event loop and asynchronous operations in Node.js are addressed.
In this document
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Introduces Node.js and the event loop concepts discussing its single-threaded, non-blocking nature.
Illustrates function calls through code examples emphasizing the Call Stack in Node.js.
Explains asynchronous programming in Node.js using setTimeout examples to show non-blocking execution.
Visual representation and explanation of the event loop's phases and its components.
Differentiates between setImmediate() and setTimeout() in terms of execution timing.
Discusses the use and functionality of process.nextTick() for immediate callback execution.
Addresses misconceptions around the event loop and asynchronous handling in Node.js.
Wrap-up and gratitude expressed with presenter details for further engagement.
Understanding the nodejs event loop
- 1. Understanding the Nodejs Eventloop myths and magic Saurabh kumar, nuLL_Programmer saurav1431@gmail.com
- 2. What is Eventloop??
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- 4. What is Node.JSand does it Works?
- 5. Well, Node.js is asingle threaded, non-blocking, asynchronous, event driven, JavaScript runtime built on V8 engine
- 6. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
- 7. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
- 8. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4));
- 9. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4)
- 10. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4) foo(8)
- 11. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4)
- 12. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4));
- 13. index.js Output: Call Stack function foo(b){ vara = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
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- 15. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); },3000); console.log(“Good Morning”); Stack
- 16. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); },3000); console.log(“Good Morning”); Stack main(); main(); console.log(“Hello”);
- 17. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); },3000); console.log(“Good Morning”); Stack main(); main(); console.log(“Good Morning”);
- 18. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); },3000); console.log(“Good Morning”); Stack main(); main();
- 19. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); },3000); console.log(“Good Morning”); Stack main(); main(); console.log(“geekle.us”);
- 20. Event loop isin picture
- 21. Event loop explained ┌───────────────────────────┐ ┌─>│timers │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ │ │ pending callbacks │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ │ │ idle, prepare │ │ └─────────────┬─────────────┘ ┌───────────────┐ │ ┌─────────────┴─────────────┐ │ incoming: │ │ │ poll │<─────┤ connections, │ │ └─────────────┬─────────────┘ │ data, etc. │ │ ┌─────────────┴─────────────┐ └───────────────┘ │ │ check │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ └──┤ close callbacks │ └───────────────────────────┘
- 22. SetImmediate() vs SetTimeout() setImmediate()is designed to execute a script once the current poll phase completes. SetTimeout() schedules a script to be run after a minimum threshold has elapsed
- 23. Process.NextTick() process.nextTick(() => { console.log(“executein next iteration.”); }) console.log(“execute in current iteration.”); Output: execute in current iteration. execute in next iteration.
- 24. When to useProcess.nextTick() 1. To allow users to handle errors. 2. Run a request before starting the next iteration of event loop, or the other event loop continues. 3. Clean unwanted resources. 4. Allow callback to run after call stack and before next iteration of event loop.
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- 26. Misconception 1: Everythingthat’s asynchronous like talking with database, working with filesystems is handled by a thread pool Reality: Libuv by default creates a thread poll with multiple thread to offload asynchronous work. Today’s operating system already provide asynchronous interfaces for many I/O tasks. Whenever possible libuv will use those interfaces avoiding usage of thread pool. But if there is no other option the thread pool will be used for asynchronous I/O/
- 27. Misconception 2: EventEmitterand Event loop are related. NodeJs event loop is the heart of Nodejs which provide non-blocking and asynchronous behaviour of an application, while eventemitter is extensively used when writing the NodeJs application.
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