JavaScript Answers

Basic JavaScript Answers

#	Question	Answer	Examples
1	What is JavaScript?	A programming language primarily used for web development	Making web pages interactive, handling events, manipulating the DOM
2	What is the purpose of JavaScript?	Adds dynamic behavior and interactivity to web pages	Responding to button clicks, updating content without reloading the page
3	What is a variable?	A container used to store data	let name = "Alice";, const age = 30;
4	How do you declare a variable?	Using let, const, or var	let count = 0;, const PI = 3.14;, var message = "Hello";
5	What is the difference between let and const?	let can be reassigned; const cannot be reassigned	let x = 1; x = 2; (valid); const y = 1; y = 2; (invalid)
6	What is a function?	A block of reusable code that performs a specific task	function greet(name) { console.log("Hello, " + name); }
7	How do you call a function?	Using the function name followed by parentheses ()	greet("Bob");
8	What is an if statement?	Executes a code block if a condition is true	if (age >= 18) { console.log("Adult"); }
9	What is an else statement?	Executes a code block if the if condition is false	if (age >= 18) { console.log("Adult"); } else { console.log("Minor"); }
10	What is a for loop?	Executes a code block a specific number of times	for (let i = 0; i < 5; i++) { console.log(i); }
11	What is a while loop?	Executes a code block as long as a condition is true	let i = 0; while (i < 5) { console.log(i); i++; }
12	What is an array?	An ordered list of items	let colors = ["red", "green", "blue"];
13	How do you access an element in an array?	Using its index (starting from 0)	console.log(colors[0]); (outputs "red")
14	What is an object?	A collection of key-value pairs (properties and methods)	let person = { name: "Charlie", age: 25 };
15	How do you access a property of an object?	Using dot notation (.) or bracket notation ([])	console.log(person.name); or console.log(person["age"]);

Intermediate JavaScript Answers

#	Question	Answer	Examples
1	What is the DOM (Document Object Model)?	A tree-like representation of an HTML document	Allows JavaScript to interact with and modify HTML elements
2	How do you select an HTML element using JavaScript?	Using methods like document.getElementById(), document.querySelector()	let myElement = document.getElementById("myId");
3	What is document.querySelector()?	Selects the first element matching a specified CSS selector	let paragraph = document.querySelector("p");
4	What is document.querySelectorAll()?	Selects all elements matching a specified CSS selector	let items = document.querySelectorAll(".item");
5	How do you change the text content of an element?	Using the textContent or innerText property	myElement.textContent = "New Text";
6	How do you change the CSS style of an element?	Using the style property	myElement.style.color = "red";
7	What is an event?	An action that occurs in the browser (e.g., click, keypress, mouseover)	click, keydown, mouseover
8	How do you attach an event listener to an element?	Using the addEventListener() method	myButton.addEventListener("click", function() { console.log("Button clicked!"); });
9	What is an arrow function?	A concise syntax for writing functions	const add = (a, b) => a + b;
10	What is the difference between function and =>?	function has its own this binding; arrow functions inherit this from parent scope	function regular() { console.log(this); }, const arrow = () => { console.log(this); }
11	What is the map() method?	Creates a new array by calling a function on every element in the original array	let numbers = [1, 2, 3]; let doubled = numbers.map(n => n * 2); (doubled is [2, 4, 6])
12	What is the filter() method?	Creates a new array with all elements that pass a test implemented by a function	let numbers = [1, 2, 3, 4, 5]; let even = numbers.filter(n => n % 2 === 0); (even is [2, 4])
13	What is the reduce() method?	Executes a reducer function on each element of the array, resulting in a single value	let numbers = [1, 2, 3]; let sum = numbers.reduce((acc, curr) => acc + curr, 0); (sum is 6)
14	What is scope?	The region where a variable is accessible	Global scope, function scope, block scope (let, const)
15	What is a closure?	A function that retains access to variables from its outer scope even after the outer function has finished	function outer(name) { function inner() { console.log(name); } return inner; }

Advanced JavaScript Answers

#	Question	Answer	Examples
1	Explain the Event Loop.	A mechanism that allows JavaScript to handle asynchronous operations without blocking execution	Call Stack, Callback Queue, Microtask Queue, Event Loop process
2	What is asynchronous JavaScript?	JavaScript code that doesn't block the main thread, allowing other tasks to run	setTimeout, setInterval, fetch, Promises, async/await
3	What is setTimeout()?	Executes a function after a specified delay (milliseconds)	setTimeout(() => { console.log("Delayed"); }, 2000);
4	What is setInterval()?	Executes a function repeatedly at a specified interval	setInterval(() => { console.log("Tick"); }, 1000);
5	What is a Promise?	An object representing the eventual completion (or failure) of an asynchronous operation	new Promise((resolve, reject) => { /_ async code _/ }).then(result => ...).catch(error => ...);
6	What is async/await?	Syntax sugar over Promises, making asynchronous code look and feel more synchronous	async function fetchData() { const response = await fetch('/api'); ... }
7	What is the this keyword?	Refers to the context in which a function is currently executing (depends on how it's called)	obj = { method: function() { console.log(this); } }; obj.method(); (this is obj)
8	Explain call(), apply(), and bind().	Methods to explicitly set the this value for a function	func.call(thisArg, arg1, arg2);, func.apply(thisArg, [arg1, arg2]);, let boundFunc = func.bind(thisArg, arg1, arg2);
9	What is a constructor function?	A function used to create and initialize new objects (often used with new)	function Person(name) { this.name = name; } let p1 = new Person("Dave");
10	Explain the concept of prototype inheritance.	JavaScript's inheritance mechanism where objects are linked to each other, sharing properties/methods	Object.prototype, Array.prototype, Person.prototype
11	What is a class (ES6)?	Syntax sugar over prototype inheritance, providing a cleaner syntax	class Animal { constructor(name) { this.name = name; } speak() { console.log(this.name); } }
12	What is the spread syntax (...)?	Expands an iterable (like an array or string) into individual elements	let arr1 = [1, 2]; let arr2 = [...arr1, 3, 4]; (arr2 is [1, 2, 3, 4])
13	What is the rest parameter (...)?	Collects remaining arguments of a function into an array	function sum(...args) { return args.reduce((a, b) => a + b, 0); }
14	What is destructuring assignment?	Extracts values from arrays or properties from objects into distinct variables	let [a, b] = [1, 2];, let { name, age } = { name: "Eve", age: 28 };
15	What is the difference between == and ===?	== performs type coercion; === does not (strict equality)	1 == "1" (true); 1 === "1" (false)