Explore topic-wise InterviewSolutions in Current Affairs.

Asynchronous programming in JavaScript is made possible by the event loop. With JS, all operations occur on a single thread, but we can create the illusion of multi-threading by using smart data structures. Event loop takes care of anything that's async using a queue and listener. 

So, when an async function has to be executed (or an I/O has to be PERFORMED), the main thread sends it to another thread, allowing v8 (Javascript engine) to continue running its code. The event loop consists of different phases with specific tasks like pending callbacks, close callbacks, timers, idle or prepare, poll, check, with different FIFO (First-In-First-Out) queues.

In an era of economic uncertainty, web development is one of the most promising careers to pursue. In spite of this, web developer interviews can be intimidating, and if you are unprepared, you will become overwhelmed and lose CONFIDENCE. In order to be competitive, you must be able to have a competitive edge and skill sets that set you apart from the REST. To be successful, you must have a thorough understanding and hands-on experience with integrating new technologies, CSS3, HTML5 APIs, front-end scripting language libraries, and LANGUAGES like JavaScript, Python, PHP, etc. Furthermore, you must be knowledgeable about configuring applications on web servers and databases, managing SEO keywords, browser compatibility and web security.

Hope you found this article informative and helpful in CLEARING your doubts. Wishing you success in your next interview.

Useful Resources:

• Web Development Projects
• Web Development Tools
• Best Web Development Books
• Web Development Course

In JavaScript, a closure is known as a JavaScript closure or JS closure. Closures allow you to access the scope (variables and parameters) of an OUTER function from an inner function. Every TIME a JavaScript function is created, a closure is created. JavaScript closures allow you to CONTROL which variables are and are not in scope in a given function, as well as which variables are shared AMONG siblings within the same CONTAINING scope.

The differences between local storage and cookies are as follows:

Media queries are used in CSS to create RESPONSIVE web designs. This MEANS that the way a web page appears varies from ONE system to another based on the screen or the media type. The media query can be used to APPLY different styles or change the appearance (and even the behaviour) of a site or an app depending on a user's device type or specific characteristics (like browser viewport width, height, screen resolution, etc.). The following can be checked using media queries:

• Dimensions (width and height) of the viewport
• Dimensions (width and height) of the device
• Orientation
• Resolution

A pseudo-class is basically used to define or specify a special state of an HTML element. This can be used in conjunction with an existing CSS selector to add effects to elements based on their state. For instance, changing the style of an element when a user hovers over it or using different STYLES for visited and unvisited links. The pseudo-class gives you the ability to do all of this.

Syntax:  

In CSS, there are many pseudo-classes, but the ones that are most FREQUENTLY used are as follows:

• :visited pseudo-class: Select the links that the user has already visited.
• :hover pseudo-class: A special effect can be added to an element when the mouse POINTER is over it.
• :active pseudo-class: Select the element that becomes active when the user clicks on it.
• :focus pseudo-class: Select an element that is CURRENTLY FOCUSED by the user.

<P>CSS selectors are used by web designers to specify or SELECT HTML elements they want to style. FOLLOWING are a few of the most COMMONLY used CSS selectors: 

• ID Selector: It selects HTML elements using specific id attributes.

Syntax: #idname

Example: Here is the CSS rule that will be applied to the HTML element having id="para1".

• Class Selector: It selects HTML elements using specific class attributes.

Syntax: .classname

Example: Here is the CSS rule that will be applied to the HTML element with class="scaler".

• Child Selector or Combinator: It selects all HTML elements that are children of the specified element. In a child selector, there are two or more selectors separated by ">".

Syntax: selector1 > selector2

Example: Here is a CSS rule that will be applied to HTML elements (<p>) that are children of a <div> element.

W3C STANDS for World Wide WEB Consortium. Founded in 1994, W3C is an INTERNATIONAL organization devoted to the improvement of the web. The W3C strives to help the web reach its full potential and ensure its continuous development. It sets standards (PROTOCOLS) for the WWW (World Wide Web) to allow for interoperability and cooperation between all stakeholders. It develops various protocols or standards as a means of growing the web.

Characteristics of W3C:

• It develops and publishes web standards or protocols.
• Furthermore, it ensures the development and growth of the web.
• In addition, it sets the standards or protocols for web scripts, web applications, and other dynamic content.
• While designing web protocols, W3C adheres to the principles of modularity, simplicity, and EXTENSIBILITY.

CDN stands for CONTENT Delivery Network. CDNs are geographically distributed groups of servers that deliver Internet content quickly. To provide end-users with fast, secure media delivery and WEB content, the servers are dispersed across many physical and network locations. Using CDNs can significantly reduce load times since they deliver files at higher bandwidth from servers located closer to your visitors than your own web server.

For faster access and better performance, web PROGRAMMERS and developers can leverage CDNs to host their jQuery LIBRARIES. Microsoft and Google have already put jQuery on their CDNs, so developers don't have to worry about that. Their only task now is to reference the hosted jQuery library.

Google CDN

Microsoft CDN

AJAX (Asynchronous JavaScript and XML) refers to a set of technologies used for developing WEB applications. The purpose of AJAX is to create better, FASTER, and more interactive web applications USING these technologies such as XML, HTML/XHTML, CSS, DOM, JavaScript, XMLHttpRequest ETC. Through Ajax, web applications are able to send and receive data asynchronously from the server without hampering the display or behaviour of the existing site. Using AJAX, you can exchange information with a server and update portions of a webpage without having to reload the whole page. The term "AJAX" refers to a technique for creating dynamic, fast web pages.

Both HTML (Hypertext Markup Language) and XHTML (Extensible Hypertext Markup Language) can be USED to create web-based and Android applications.

Managing the availability of variables or objects in an application is governed by the concept of scope. In JavaScript, there are two types of scope as follows:

Global Scope: A variable having global scope can be accessed from anywhere in the program. These variables that are DECLARED OUTSIDE of any FUNCTION can be accessed from any place in the program.

Example:

Local Scope: Variables with a local scope can only be accessed WITHIN the same function in which they are declared. Whenever a variable is declared inside a function, it becomes local to the function. As soon as a function begins, local variables are created and deleted when the function is executed.

Example:

Javascript uses pop-up boxes to display notifications and messages to users. Here are the different types of pop-up boxes in Javascript:

• Alert BOX: This is used to display a warning message. After the alert box appears, the user needs to press the OK BUTTON to proceed.

Syntax: 

Example: Running the FOLLOWING script will open an alert box that contains the message: "This is Scaler Academy" along with a confirmation button OK.

• Confirm Box: These pop-up boxes are used as a means of obtaining authorization or permission from the user. In order to proceed, the user must click the OK or Cancel button.

Syntax: 

Example: Upon executing the following script, it will open a confirmation box containing the following text: "Confirm this action" along with a confirmation button and cancellation button. Based on the input provided by the user, this returns a boolean. It will return true if the user clicks to confirm, and false if the user clicks cancel.

• Prompt Box: The purpose of this type of pop-up box is to gather user input for further USE. After entering the necessary information, the user has to click OK to proceed to the next stage, otherwise PRESSING the Cancel button returns the null value.

Syntax:  

Example: Running the following script will open a pop-up box with the message: "Enter your email". There will also be a confirmation button and a cancellation button.

You'll be able to see your email on the console once you enter some input in the prompt box.

NPM stands for NODE Package Manager. It is commonly used as a default package manager for Node.js (JavaScript runtime environment). It is included in every installation of Node.js. This command-line tool installs, updates, and uninstalls Node.js packages and modules required for Node applications or projects. A package CONTAINS all files for a module, and modules are basically JavaScript libraries that can be added to a Node project as needed. It contains a number of libraries that are extremely USEFUL to Node.js developers, speeding up the process of developing applications.

Installing NPM: In order to install NPM, you need to install Node.js as NPM automatically gets with Node.js.

Check NPM Version: The FOLLOWING syntax can be used to check the version of NPM that is installed on the system:

Syntax: npm -v

Update NPM Version: NPM updates refer to updating the Node package manager to its latest version. One may always update the installed version if it is not the latest using the syntax given below:

Syntax: npm update [-g] [<PKG>...]

The -g flag is used to update npm globally since it is a global package and pkg refers to the package.

• Use npm@update command

• Use update command

• Use npm@latest command

As a Web Developer, here are the top hacks for reducing load TIME and optimizing your web application's loading times:

• Image compression and OPTIMIZATION: Using images on your website will improve the appearance and quality of your pages. However, larger images will also slow down the loading process. Compressing and optimizing images is ONE of the easiest ways to improve the speed of your site. The smaller your images' file sizes, the less weight they have, which, in turn, helps your pages load faster.
• Put JavaScript and CSS in external files: When JavaScript and CSS are embedded in HTML documents, they are downloaded each time the HTML document is loaded. As a result, this does not utilize browser caching, increasing the size of HTML documents. You should always place CSS and JavaScript in external files; this is best practice and makes maintaining your site easier.
• Reduce the number of redirects: A website with too MANY redirects will take a long time to load. HTTP request and response times are prolonged every time a page redirects. If you eliminate unnecessary redirects on your site, your page load time will be significantly reduced.
• CSS and JavaScript files should be loaded asynchronously: You have CSS and JavaScript files on your website that can be loaded synchronously or asynchronously. In synchronous loading, each file is loaded one at a time, in the order in which it appears on your web page. Asynchronous loading, on the other hand, allows multiple files to be loaded simultaneously, which can speed up the performance of a website. '
• Minify HTML, CSS, and JavaScript: Your pages will load faster if you optimize how your files to load. In a similar vein, you can minify your HTML, CSS, and JavaScript code. You can reduce the size of files by eliminating unnecessary spaces, characters, comments, and other components. As a result, web pages will load faster with cleaner code.

Typically, it depends on how your SITE is laid out and how users interact with it. The most efficient way, however, would be to use just a SINGLE file called styles.CSS (or something similar). Combining them into a single document is preferable. Loading one file is easier for a client than loading five. In order to change the style, you SIMPLY open the styles.css file, scroll down to find the appropriate section, and modify the CSS. The sheet can be linked in your HTML as follows: