JavaScript Questions and Answers for Viva

Answer-1: JavaScript is a lightweight, interpreted programming language primarily used to create interactive web pages.

Answer-2: JavaScript is a scripting language, while Java is a programming language used for application development.

Answer-3: Data types include Number, String, Boolean, Object, Undefined, Null, Symbol, and BigInt.

Answer-4: == checks value equality, while === checks both value and type equality.

Answer-5: A variable is a container for storing data values.

Answer-6: let and const have block scope, while var has function scope. const is used for constants.

Answer-7: Control structures include if, else, switch, for, while, and do-while.

Answer-8: A function is a block of reusable code that performs a specific task.

Answer-9: Function declarations are hoisted, while function expressions are not.

Answer-10: Arrow functions are a concise syntax for writing functions, introduced in ES6.

Answer-11: An object is a collection of properties, where each property has a key and a value.

Answer-12: this refers to the context in which a function is executed.

Answer-13: null represents an intentional absence of value, while undefined means a variable is declared but not initialized.

Answer-14: An event is an action or occurrence that can be detected by JavaScript, such as a click or a keypress.

Answer-15: Use square brackets [] or the Array constructor.

Answer-16: Common methods include push(), pop(), shift(), unshift(), map(), filter(), and reduce().

Answer-17: forEach executes a function for each array element; map returns a new array with transformed elements.

Answer-18: A promise is an object representing the eventual completion or failure of an asynchronous operation.

Answer-19: Primitive types include Number, String, Boolean, Undefined, Null, Symbol, and BigInt.

Answer-20: Synchronous code executes line by line, while asynchronous code allows other operations to run in parallel.

Answer-21: The DOM (Document Object Model) is a programming interface for HTML and XML documents.

Answer-22: Use methods like getElementById, querySelector, appendChild, and removeChild.

Answer-23: An event listener is a function that executes when an event occurs.

Answer-24: call and apply invoke functions with a specified this context; bind returns a new function.

Answer-25: Closures are functions that have access to their outer function's variables, even after the outer function has returned.

Answer-26: A callback is a function passed as an argument to another function and executed later.

Answer-27: The typeof operator returns the type of a variable.

Answer-28: Hoisting is JavaScript's behavior of moving declarations to the top of their scope.

Answer-29: slice() returns a new array without modifying the original; splice() modifies the original array.

Answer-30: JSON.stringify() converts objects to JSON strings; JSON.parse() converts JSON strings to objects.

Answer-31: let has block scope, while var has function scope and is hoisted.

Answer-32: Modules are reusable pieces of JavaScript code that can be exported and imported between files.

Answer-33: == allows type coercion; === does not allow type coercion.

Answer-34: The spread operator (...) allows an iterable to be expanded into individual elements.

Answer-35: Error types include SyntaxError, TypeError, ReferenceError, and RangeError.

Answer-36: The fetch API is used to make HTTP requests and handle responses in JavaScript.

Answer-37: localStorage persists data until manually cleared; sessionStorage clears data when the browser tab is closed.

Answer-38: async functions return promises, and await pauses the execution until the promise is resolved.

Answer-39: var has function scope; let and const have block scope. const is used for immutable variables.

Answer-40: Template literals are strings that allow embedded expressions, written with backticks (`).

Answer-41: null is explicitly assigned, while undefined is the default value for uninitialized variables.

Answer-42: A symbol is a unique, immutable primitive value, often used as object property keys.

Answer-43: use strict enforces stricter parsing and error handling in JavaScript.

Answer-44: setTimeout runs a function once after a delay; setInterval runs a function repeatedly at intervals.

Answer-45: Promise.all() resolves when all promises in an array are resolved or any of them is rejected.

Answer-46: Event delegation involves adding a single event listener to a parent element to handle events on its children.

Answer-47: window represents the browser window; document represents the HTML document.

Answer-48: Object.freeze() makes an object immutable, preventing modifications to its properties.

Answer-49: A polyfill is code that provides modern functionality in older browsers that do not support it.

Answer-50: Higher-order functions take other functions as arguments or return functions as results.