#NODEJS EVENT LOOP HOW TO#
#NODEJS EVENT LOOP INSTALL#
#NODEJS EVENT LOOP UPDATE#

The file loads and the main function is being called, which stands for the execution of the entire file.

The steps of the previous example are the following: The order in which the stack processes each function call follows the LIFO principle (Last In, First Out). Note how each function call is being added to the call stack and removed once it finishes.Įvery time a function calls another function, it's added to the top of the stack, on top of the calling function. I created this small visualization to make it easier to understand: The call stack is a mechanism that helps the JavaScript interpreter to keep track of the functions that a script calls.Įvery time a script or function calls a function, it's added to the top of the call stack.Įvery time the function exits, the interpreter removes it from the call stack.Ī function either exits through a return statement or by reaching the end of the scope. JavaScript can do one single thing at a time because it has only one call stack. You've probably already heard that JavaScript is single-threaded. Web APIs, the callback queue, and the event loop are all features that the browser provides.Ī representation of NodeJS would look similar, but in this article, I'll focus on how JavaScript works in the browser. Note how most of the things in the graphic aren't part of the JavaScript language itself. I will cover each of them in this section.

Uncaught RangeError: Maximum call stack size exceededīefore I dive into the explanation of each topic, I want you to look at this high-level overview that I created, which is an abstraction of how JavaScript interacts with the browser.ĭon't worry if you don't know what all of the terms mean.

The Event Loop :Once the Call Stack is empty, the event loop keeps checking the CallBack Queue for executing the asynchronous functions. The items present in the callback queue are only called, when the call stack becomes empty. The CallBack Queue :The Callback queue holds the asynchronous functions which are ready to be executed (i.e the long waiting period is done). Once the data/requests are processed, the browser sends it to the CallBack Queue. Node/Web API’s :Any function which is not related to JavaScript, like HTTP requests are given to the browser which uses C++ for processing it. When a function is done performing it’s job, it gets removed from the call stack. The first function to be invoked is the main function. The Call Stack :Any Node.js function, when invoked, goes into the call stack. Well, let’s get deeper into the internal working of Node.js. But why did “I should wait for 0 seconds before execution” print after “It’s time for me to end”.

#NODEJS EVENT LOOP HOW TO#

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#NODEJS EVENT LOOP INSTALL#

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#NODEJS EVENT LOOP UPDATE#

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Nodejs event loop