![]() These are libraries built by the awesome community which will solve most of your generic problems. So it moves the callbacks (in a first-in-first-out order) to the call stack for execution. The event loop sees that the call stack is empty and the callback queue is not empty.The last console.log() runs, and the main() gets popped from the call stack.In the callback queue, the functions wait for the call stack to be empty, because only one statement can execute a time.After waiting for 0 seconds, setTimeout(0) gets moved to the callback queue, and the same thing happens with setTimeout(2000).We now have two Node APIs waiting to execute. Now the second setTimeout(0) gets registered in the same way.After registering it in the APIs, setTimeout(2000) gets popped from the call stack.The event will wait 2000 milliseconds, then callback is the function. When we call it, we register the event-callback pair. This then runs right away and gets popped. ![]() Push console.log() onto the call stack.Otherwise, here’s a quick step-by-step explanation of how the JavaScript Event Loop works. If you have 26 minutes, watch this excellent video explanation of the Node Event Loop: Blocking I/O (left) vs Non-Blocking I/O (right) The response to this request takes time, but both of the user data requests can be carried out independently and at the same time. I/O takes time and hence blocks other functions.Ĭonsider a scenario where we request a backend database for the details of user1 and user2 and then print them on the screen/console. It can be anything ranging from reading/writing local files to making an HTTP request to an API. We already discussed the first line of this definition: “Node.js® is a JavaScript runtime built on Chrome’s V8 JavaScript engine.” Now let’s understand the other two lines so we can find out why Node.js is so popular. Node.js’ package ecosystem, npm, is the largest ecosystem of open source libraries in the world. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient. Here’s a formal definition as given on the official Node.js website: Node.js® is a JavaScript runtime built on Chrome’s V8 JavaScript engine. Machine code is low-level code which the computer can run without needing to first interpret it. This engine takes your JavaScript code and converts it into a faster machine code. JavaScript now has the capability to do things that other scripting languages like Python can do.īoth your browser JavaScript and Node.js run on the V8 JavaScript runtime engine. Now you can do much more with JavaScript than just making websites interactive. Node.js came into existence when the original developers of JavaScript extended it from something you could only run in the browser to something you could run on your machine as a standalone application. If you know Java, here’s a little analogy. The Node.js run-time environment includes everything you need to execute a program written in JavaScript. Sounds great, but what does that mean? How does that work? Node.js is a JavaScript runtime environment.
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