JavaScript interviews focus on core concepts, hands-on coding problems, and real-world logic. You should be comfortable with variables, functions, scope, closures, arrays, objects, asynchronous JavaScript, ES6 features, and writing clean code to solve interview-level problems.<\/p>\n\n\n\n
JAVASCRIPT OVERVIEW QUESTIONS<\/h2>\n\n\n\n
Before diving into the next section, ensure you’re solid on full-stack development essentials like front-end frameworks, back-end technologies, and database management. If you are looking for a detailed full-stack development career program, you can join HCL GUVI\u2019s Full Stack Development Course<\/strong><\/a> with Placement Assistance. You will be able to master the MERN stack<\/a> (MongoDB, Express.js, React, Node.js) and build real-life projects.<\/em> <\/p>\n\n\n\n Additionally, if you want to explore JavaScript through a self-paced course, try HCL GUVI\u2019s JavaScript certification course<\/a>. <\/strong><\/em><\/p>\n\n\n\n Ans. JavaScript is the world’s most popular programming language. Above all, it is the programming language mainly used in the Web Development domain, and is commonly implemented for creating web pages. <\/p>\n\n\n\n JavaScript is a <\/p>\n\n\n\n JavaScript was invented by Brendan Eich in 1995. It was developed for Netscape 2 and became the ECMA-262 standard in 1997.<\/p>\n\n\n\n It is commonly used for creating web pages. JavaScript allows us to add dynamic behavior to the webpage and add special effects to it. On websites, JavaScript is mainly used for validation purposes.<\/p>\n\n\n\n It is widely used, supported & accessible even to beginners.<\/p>\n<\/div><\/div>\n\n\n\n Ans. JavaScript can be implemented in three different ways, namely<\/p>\n\n\n\n \u2022 Embedding code Ans. In JavaScript, an object is a standalone entity with properties and a type. Compare it with a cup, <\/p>\n\n\n\n for example. A cup is an object with properties. A cup has a color, a design, a weight, etc.<\/p>\n\n\n\n JavaScript properties: In the same way, JavaScript objects can have properties, which define their characteristics<\/p>\n<\/div><\/div>\n\n\n\n Ans. The change in the state of an object is known as an Event. In HTML, various events represent that some activity is performed by the user or by the browser.<\/p>\n\n\n\n When JavaScript code is included in HTML, JavaScript reacts to these events and allows the execution. This process of reacting to the events is called Event Handling. Thus, JS handles the HTML events via Event Handlers.<\/p>\n\n\n\n Common events are:<\/p>\n\n\n\n \u2022 onLoad – occurs when a page loads in a browser Other examples include events like pressing any key, closing a window, resizing a window, etc. <\/p>\n\n\n\n Let’s move ahead. With more interesting JavaScript Questions. <\/p>\n\n\n\n JavaScript is a multi-paradigm language, supporting imperative\/procedural programming along with OOP (Object-Oriented Programming) and functional programming. JavaScript supports OOP with prototypal inheritance.<\/p>\n<\/div><\/div>\n\n\n\n Functional programming produces programs by composing mathematical functions. Furthermore, it avoids shared state & mutable data.<\/p>\n\n\n\n Lisp (specified in 1958) was among the first languages to support functional programming and was heavily inspired by the lambda calculus. Functional programming is an essential concept in JavaScript (one of the two pillars of JavaScript). <\/p>\n\n\n\n Several common functional utilities were added to JavaScript in ES5. – Function purity <\/p>\n\n\n\n – Avoiding side-effects <\/p>\n\n\n\n – Simple function composition<\/p>\n<\/div><\/div>\n\n\n\n Class Inheritance:<\/strong> Instances inherit from classes (like a blueprint – a description of the class), and create sub-class relationships: hierarchical class taxonomies. Instances are typically instantiated via constructor functions with the new keyword. In short, Class inheritance may or may not use the class keyword from ES6.<\/p>\n\n\n\n There is more than one type of prototypal inheritance: Synchronous programming <\/strong>means that, barring conditionals and function calls, code is executed sequentially from top to bottom, blocking on long-running tasks such as network requests and disk I\/O. <\/p>\n\n\n\n Whereas Asynchronous programming<\/strong> means that the engine runs in an event loop. When a blocking operation is needed, the request is started, and the code keeps running without blocking for the result. <\/p>\n\n\n\n When the response is ready, an interrupt is fired, which causes an event handler to be run, where the control flow continues. In this way, a single program thread can handle many concurrent operations. <\/p>\n\n\n\n User interfaces<\/strong> are asynchronous by nature and spend most of their time waiting for user input to interrupt the event loop and trigger event handlers. Node is asynchronous by default. That means the server works in much the same way, waiting in a loop for a network request. And accepting more incoming requests while the first one is being handled. <\/p>\n\n\n\n This is important in JavaScript because it is a very natural fit for user interface code and very beneficial to performance on the server.<\/p>\n<\/div><\/div>\n\n\n\n In JavaScript, there are <\/p>\n\n\n\n 3 Primary Data Types: <\/strong><\/p>\n\n\n\n String, <\/p>\n\n\n\n Number, <\/p>\n\n\n\n Boolean.<\/p>\n\n\n\n Then, 4 Composite Data Types <\/strong><\/p>\n\n\n\n Object<\/p>\n\n\n\n Functions<\/p>\n\n\n\n Date, <\/p>\n\n\n\n Array.<\/p>\n\n\n\n And, two data types that cannot contain any values: <\/strong><\/p>\n\n\n\n Null and <\/p>\n\n\n\n Undefined<\/p>\n<\/div><\/div>\n\n\n\n “==” checks only for equality in value, whereas “===” is a stricter equality test and returns false if either the value or the type of the two variables are different. <\/p>\n\n\n\n So, the second option needs both the value and the type to be the same for the operands.<\/p>\n<\/div><\/div>\n\n\n\n Undefined value means the: There are three types of errors: Errors that come up when loading a web page, like improper syntax errors, are known as load-time errors, and it generated the errors dynamically.<\/p>\n\n\n\n Errors that come due to the misuse of the command inside the HTML language<\/a>.<\/p>\n\n\n\n1<\/span>. What is JavaScript?<\/span><\/strong><\/h3>\n\n\n\n
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2. How to implement JavaScript<\/strong>?<\/span><\/h3>\n\n\n\n
\u2022 Inline code
\u2022 External file<\/p>\n<\/div><\/div>\n\n\n\n3. How do you write JavaScript? <\/strong><\/mark><\/h3>\n\n\n\n
Ans. JavaScript code is embedded in the HTML. The client browsers can then interpret and run them.<\/p>\n\n\n\n\n
4. What are Objects in JavaScript?<\/strong><\/mark><\/h3>\n\n\n\n
5. What are JavaScript Events?<\/span><\/strong><\/h3>\n\n\n\n
\u2022 onUnload – occurs just before the user exits a page
\u2022 onMouseOver – occurs when you point to an object
\u2022 onMouseOut – occurs when you point away from an object
\u2022 onSubmit – occurs when you submit a form
\u2022 onClick – occurs when an object is clicked<\/span><\/strong><\/p>\n<\/div>\n<\/div>\n\n\n\n
JavaScript\u2019s interaction with HTML is handled through events that occur when the user or the browser manipulates a page. When the page loads, it is called an event. When the user clicks a button, that click is an event. <\/p>\n\n\n\n
Developers can use these events to execute JavaScript-coded responses, which cause buttons to close windows, messages to be displayed to users, data to be validated, and virtually any other type of response imaginable. Events are a part of the Document Object Model (DOM) Level 3 and every HTML element contains a set of events that can trigger JavaScript Code.<\/p>\n<\/div><\/div>\n\n\n\nTheoretical JavaScript Questions<\/h2>\n\n\n\n
6. Can you name any two programming paradigms important for JavaScript app developers?<\/strong><\/mark><\/h3>\n\n\n\n
7. What is functional programming?<\/strong><\/mark><\/h3>\n\n\n\n
The core focus lies on:<\/p>\n\n\n\n8. What is the difference between classical inheritance and prototypal inheritance?<\/span><\/strong><\/h3>\n\n\n\n
![\"Decoding](\"https:\/\/miro.medium.com\/max\/1200\/1*dianRzNAQevG4-ZXUfxpDg.png\" "\\"\\"")
Prototypal Inheritance: <\/strong>Instances inherit directly from other objects. Instances are typically instantiated via factory functions or Object.create(). Instances may be composed of many different objects, allowing for easy selective inheritance.<\/p>\n<\/div><\/div>\n\n\n\n9. When is prototypal inheritance an appropriate choice?<\/strong><\/mark><\/h3>\n\n\n\n
\u2022 Delegation (i.e., the prototype chain).
\u2022 Concatenative (i.e. mixins, Object.assign()).
\u2022 Functional (Not to be confused with functional programming. A function used to create a closure for private state\/encapsulation).<\/p>\n\n\n\n
Each type of prototypal inheritance has its own set of use cases. However, all of them are equally useful in their ability to enable composition. That will create has-a or uses-a or can-do relationships as opposed to the is-a relationship created with class inheritance.<\/p>\n<\/div><\/div>\n\n\n\n10. What is asynchronous programming, and why is it important in JavaScript?<\/span><\/strong><\/h3>\n\n\n\n
11. What are JavaScript data types?<\/mark><\/h3>\n\n\n\n
![\"What](\"http:\/\/blog.guvi.in\/wp-content\/uploads\/2022\/01\/Data-Types-in-Javascript-1024x726.png\" "\\"\\"")
<\/figure>\n\n\n\n12. What is the difference between “==” and “===”?<\/mark><\/h3>\n\n\n\n
13. What is an undefined value in JavaScript?<\/mark><\/h3>\n\n\n\n
\u2022 The variable used in the code doesn\u2019t exist
\u2022 Furthermore, the variable is not assigned to any value
\u2022 Property doesn\u2019t exist<\/p>\n<\/div><\/div>\n\n\n\n14. What are the different types of errors in JavaScript?<\/mark><\/h3>\n\n\n\n
\u2022 Load time errors: <\/strong><\/p>\n\n\n\n
\u2022 Run-time errors: <\/strong><\/p>\n\n\n\n