Who gets the callback when onreadystatechange is triggered in a single-threaded JavaScript environment?

Having recently delved into the world of JavaScript, I've come across the fact that it is single-threaded. My initial assumption was that when making an asynchronous request, a separate thread would be started to monitor the server's response. However, as I've learned, this approach doesn't work in JavaScript. I'm now wondering if there is some built-in mechanism that stores all listeners and executes them based on certain conditions they've "agreed" to (onreadystatechange).

I realize that my previous thinking may be completely off base. If anyone can provide some guidance or clarification, I'd greatly appreciate it.

javascriptajax

Answer №1

Even though JavaScript execution is single-threaded, there could be multiple threads used by the underlying engine. This concept is further explained in this resource.

For instance, while an HTTP request may have its own thread within the browser, any resulting events are placed in a queue for the JS task scheduler. Once the current script finishes running, the appropriate event handler like onreadystatechange will be invoked.

Answer №2

Each browser has its own way of handling the XHR object - for example, IE uses ActiveX while FF uses XMLHttpRequest. Although there are attempts in HTML5 to standardize this with the introduction of the XHR2 object, widespread support is still lacking. This means that implementation varies across browsers, some using threads and others different methods. While JavaScript is generally single-threaded, asynchronous programming is still possible without manual thread creation.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Tips for inserting HTML into elements using Angular

Recently, I delved into Angular and decided to experiment with Ajax by fetching a document to display on my webpage. The process worked flawlessly, but now I face a new challenge: injecting HTML content into a DOM element dynamically. Typically, this task ...

javascripthtmlangularjs

Firestore TimeStamp.fromDate is not based on UTC timing

Does anyone have a solution for persisting UTC Timestamps in Firestore? In my Angular application, when I convert today's date to a Timestamp using the code below, it stores as UTC+2 (due to summer time in Switzerland). import {firebase} from ' ...

javascriptangulardatetimegoogle-cloud-firestore

Even though the onSubmit attribute is set to false in the HTML form, it still submits

I've been struggling with a form that just won't stop submitting, no matter what I do. I have checked similar questions on SO, but none of the solutions seem to work for me. It's frustrating because it's such a simple task. The reason w ...

javascriptjqueryhtmlvalidation

Is the information not displayed in its entirety on the FullCalendar?

I'm currently working with the following code: $('#calendar_1').fullCalendar({ header : { left : 'prev,next today', center : 'title', right : 'month,agendaWeek,agendaDay' ...

javascriptphpajaxfullcalendar

Express POST request body is required

I am starting to learn nodejs and express, and while reviewing some code I found this interesting snippet. Can someone please explain what it means and how I can send a POST request to it using cURL? There are no specified data fields. app.post('/&apo ...

javascriptnode.jsexpresscurlmiddleware

Where can Vue.js be found?

After dedicating an hour to watching instructional YouTube videos on Vue.js, I am still struggling to grasp the language! In the past, I have worked with Node.js, Jquery, and Mongodb to develop websites... I believe that web applications require multiple ...

javascriptnode.jsvue.jsejs

Tips on invoking a Stencil component function or method from beyond the Vue instance

Is it possible to trigger a function in a Stencil component from the parent Vue instance? For example, I would like to call the callChild() method in the Vue instance, which will then trigger the doSomething() function in the Stencil component. The main ...

javascriptvue.jsvuejs2vue-clistenciljs

How can a loading circle be displayed upon clicking a button on a PHP website using JavaScript?

As a newcomer to the world of JavaScript programming, I'm facing a challenge that seems deceptively simple. My goal is to display a loading circle when a user clicks on an upload button, trigger external PHP code for image processing, and then make th ...

javascriptphpajaxweb

What could be causing spacing problems with fontawesome stars in Vue/Nuxt applications?

Currently, I am working on implementing a star rating system in Nuxt.js using fontawesome icons. However, I have encountered an issue where there is a strange whitespace separating two different stars when they are placed next to each other. For instance, ...

javascriptcssvue.jsnuxt.jsfont-awesome

Dealing with code issues in Subscription forms using AJAX and JQuery

Currently, I am independently studying jQuery and grappling with the Mailchimp Opt-In form code. Despite various existing queries on this topic, I am curious about why my own implementation, as a beginner in jQuery, is not functioning correctly. My intenti ...

javascriptjqueryajaxforms

Setting up node.js for angular - serving static files with connect.static and running unit tests

Currently, I am in the process of setting up a basic node webserver by following a tutorial outlined in Pro AngularJS published by Apress. Node.js along with both the connect and karma modules have been successfully installed on my system. During the ins ...

javascriptangularjsnode.jsnpmkarma-runner

Guide to incorporating HTML within React JSX following the completion of a function that yields an HTML tag

I am currently working on a function that is triggered upon submitting a Form. This function dynamically generates a paragraph based on the response received from an Axios POST request. I am facing some difficulty trying to figure out the best way to inje ...

javascriptreactjsjsx

Assess html code for Strings that include <% %> tags along with embedded scripts

Having a small issue with my code where I am receiving an HTML response from a web service as a java String. I need to display this String as HTML on my webpage, but the problem is that there are some script tags in the form of <% ... %> which are sh ...

javascriptjavahtmlstringescaping

Exploring the distinctions between ajax, await, async, and

English is not my strong suit, so please bear with me if my writing seems odd. We have discovered two methods for transitioning from asynchronous ajax calls to synchronous ones. Using async: false Utilizing await Both achieve the same outcome, but I am ...

javascriptajaxfunctionasync-awaitsynchronization

When implementing Firebase Cloud Messaging with React, the token generated by firebase.messaging().getToken() will vary with every refresh

I'm working on a React web app using Gatsby and I want to integrate push notifications through FCM. My firebase-messaging-sw.js service worker is set up, and I'm trying to retrieve a token using the following method in my app: messaging .req ...

javascriptreactjsfirebasefirebase-cloud-messaginggatsby

Refresh gif without having to reload it in Internet Explorer 11

I'm attempting to create a feature where a gif restarts when clicked by the user, without needing to reload it (due to the heavy size of the gif which is preloaded for my application). The current code functions flawlessly on Chrome and other "modern ...

javascripthtmlinternet-explorergif

The React loader fails to function properly when used with nested routes

I'm currently working on my App.js file where I have defined all the routes for my application. I wanted to implement React-Router data loader functionality. import React from 'react' import { Routes, Route, Navigate, RouterProvider, createB ...

javascriptreactjsreact-routerreact-router-dom

What is the best way to cause a ball to collide with a triangle power-up on a canvas

I'm currently facing an issue with the power up feature in my game. Despite successfully displaying the shape on screen, the ball fails to speed up as expected upon collision with the shape. <html> <title>Level Selector</title& ...

javascripthtmlcanvashtml5-canvas

HTML not being able to execute Javascript when using an SSL connection

While serving HTML via Jenkins HTTPS with an invalid security certificate, the following code is included: <!DOCTYPE html> <html> <head> <script type="text/javascript">alert(1);</script> <script type="text/javascri ...

javascripthtmlssljenkins

When setting up Vue.js for unit testing, the default installation may show a message stating that

Recently set up a fresh Vue project on Windows 7 using the VueJS UI utility. Unit testing with Jest enabled and added babel to the mix. However, when running "npm test" in the command line, an error is returned stating 'Error: no test specified' ...

javascriptnode.jsunit-testingvue.jsbabeljs