Javascript Interview Questions Mcq
Web Development Interview MCQs: Common JavaScript Questions
JavaScript is a dynamic, client-side scripting language used for creating interactive web applications. As it is widely used by web developers, job seekers may encounter a variety of interview questions related to JavaScript. These questions may cover topics such as data types, functions, control structures, looping, DOM manipulation, Ajax, and error handling. Some common JavaScript interview questions may include explaining the difference between null and undefined, how to declare variables, how to use object-oriented programming in JavaScript, and how to handle cross-site scripting (XSS) attacks. Candidates should have a solid understanding of the language and be able to explain their thought process while solving problems using JavaScript.
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1 - What is JavaScript?
JavaScript is a high level scripting language used for creating interactive webpages. It is primarily used to add functionality and interactivity to websites.
2) What are the key features of JavaScript?
Dynamic and flexible: JavaScript allows for dynamic behavior and modifications to a webpage without reloading.
Client side execution: JavaScript is executed on the client side, meaning it runs on the user's browser rather than the server.
Platform independent: JavaScript can run on any device or operating system.
Lightweight and interpreted: JavaScript is a lightweight language and does not require compiling, making it easier to use and debug.
3) What is the difference between == and === in JavaScript?
The == operator only checks for value equality, while === checks for both value and type equality.
4) What is the use of typeof operator?
The typeof operator is used to check the data type of a variable or expression in JavaScript.
5) What is the purpose of the “use strict” directive in JavaScript?
The “use strict” directive enables strict mode, which helps prevent errors and promote more secure coding practices.
6) How do you declare variables in JavaScript?
Variables in JavaScript can be declared using the var, let, or const keywords. Var allows for redeclaration and name conflicts, let allows for reassignment but not redeclaration, and const is used for declaring constants that cannot be changed.
7) What is event bubbling in JavaScript?
Event bubbling is a propagation mechanism in which an event is handled first by the innermost element and then propagated to the outer elements.
8) What are closures in JavaScript?
Closures are functions that have access to variables defined in their outer scope even after the outer function has returned.
9) What is a callback function in JavaScript?
A callback function is a function passed as an argument to another function, which is then executed after a certain event or action.
10) What is the difference between let and var in JavaScript?
Variables declared with var are function scoped, while variables declared with let are block scoped.
11) Explain the difference between a null value and an undefined value in JavaScript.
Null represents an intentional absence of value, while undefined means the value has not been initialized or assigned.
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12) What is event delegation in JavaScript?
Event delegation is a technique where a parent element handles events on behalf of its child elements, reducing the need for adding event listeners to each child element.
13) How do you handle errors in JavaScript?
JavaScript has a try…catch statement that allows for handling errors and throwing custom errors using the throw keyword.
14) How does JavaScript handle inheritance?
JavaScript uses prototype based inheritance, where objects inherit properties and methods from their prototype.
15) What are the benefits of using JavaScript?
Increased interactivity and user experience on websites
Enhanced form validation and error handling
Reduction in server calls and improved website performance
Compatibility with multiple browsers and devices
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