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<\/a><\/p>Practice JavaScript Interview Questions and Answers<\/h2>
Below are the top 50 Javascript interview questions for freshers with answers:<\/p>
1. What is JavaScript, and how is it different from Java?<\/h3>
Answer:<\/strong><\/p> JavaScript is a scripting language primarily used for web development, whereas Java is a full-fledged programming language.<\/p> \/\/ Example of JavaScript code Answer:<\/strong><\/p> JavaScript evolved from a simple scripting language to a powerful tool with features like ES6, async programming, and modules.<\/p> Answer:<\/strong><\/p> Install Node.js for server-side development and use a code editor like VSCode for writing JavaScript code.<\/p> node –version<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> JavaScript in the browser is used for client-side interactions, while Node.js runs JavaScript on the server side.<\/p> Answer:<\/strong><\/p> Use console.log()<\/strong> to print messages to the console.<\/p> console.log(“Hello, World!”);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> var<\/strong> is function-scoped, let<\/strong> and const are block-scoped, with const<\/strong> being immutable.<\/p> let name = “John”; Answer:<\/strong><\/p> ==<\/strong> checks for value equality, while ===<\/strong> checks for both value and type equality.<\/p> console.log(5 == ‘5’); \/\/ true Answer:<\/strong><\/p> Use alert()<\/strong> to show messages, prompt()<\/strong> to get user input, and confirm()<\/strong> to get confirmation.<\/p> alert(“Hello!”); Answer:<\/strong><\/p> Primitive data types include string<\/strong>, number<\/strong>, boolean<\/strong>, null<\/strong>, undefined<\/strong>, and symbol<\/strong>.<\/p> let num = 42; Answer:<\/strong><\/p> Use the +<\/strong> operator to sum two numbers.<\/p> let a = 5; Answer:<\/strong><\/p> Use if-else<\/strong> to conditionally check and execute code based on the number’s value.<\/p> let num = -5; Answer:<\/strong><\/p> switch<\/strong> is used for multiple conditions based on a single variable, offering a cleaner alternative to multiple if-else<\/strong> statements.<\/p> let day = 2; Answer:<\/strong><\/p> Use a for<\/strong> loop to iterate from 1 to 10 and print each number.<\/p> for (let i = 1; i <= 10; i++) { Answer:<\/strong><\/p> while<\/strong> loops check the condition before execution, while do-while<\/strong> loops execute the block at least once before checking the condition.<\/p> let i = 1; Answer:<\/strong><\/p> Use continue<\/strong> to skip odd numbers and print only even numbers.<\/p> for (let i = 1; i <= 20; i++) { Answer:<\/strong><\/p> Function declarations are hoisted, while function expressions are not.<\/p> function greet() { const greetExpression = function() { Answer:<\/strong><\/p> Parameters are placeholders in the function definition, while arguments are the actual values passed to the function.<\/p> function add(a, b) { console.log(add(5, 10)); \/\/ 15<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> The return<\/strong> statement exits the function and optionally returns a value to the caller.<\/p> function multiply(a, b) { let result = multiply(3, 4); \/\/ 12<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Arrow functions are a shorter syntax for functions and do not have their own this<\/strong> context.<\/p> const sum = (a, b) => a + b;<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> IIFEs are functions that execute immediately after they are defined.<\/p> (function() { Answer:<\/strong><\/p> Create an object using curly braces {}<\/strong> and access properties using dot notation or bracket notation.<\/p> let person = { name: “John”, age: 30 }; Answer:<\/strong><\/p> this<\/strong> refers to the object that is currently calling the method or the global object in a function.<\/p> let person = { person.greet(); \/\/ John<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> push<\/strong> adds to the end, pop<\/strong> removes from the end, shift<\/strong> removes from the beginning, and unshift<\/strong> adds to the beginning of an array.<\/p> let arr = [1, 2, 3]; Answer:<\/strong><\/p> map<\/strong> returns a new array with the results of calling a function on every element, while forEach<\/strong> executes a function on each element without returning a new array.<\/p> let arr = [1, 2, 3]; Answer:<\/strong><\/p> Use the filter()<\/strong> method to create a new array with elements that pass a test.<\/p> let numbers = [1, 2, 3, 4, 5, 6]; Answer:<\/strong><\/p> Use the length<\/strong> property to find the number of characters in a string.<\/p> let str = “Hello, World!”; Answer:<\/strong><\/p> Use the toUpperCase()<\/strong> method to convert a string to uppercase.<\/p> let str = “hello”; Answer:<\/strong><\/p> Both slice()<\/strong> and substring()<\/strong> extract parts of a string, but slice()<\/strong> can accept negative indices.<\/p> let str = “Hello, World!”; Answer:<\/strong><\/p> Template literals allow embedding expressions inside strings using backticks “<\/strong> and ${}<\/strong>.<\/p> let name = “John”; Answer:<\/strong><\/p> Use the replace()<\/strong> method with a regular expression to replace all occurrences of a substring.<\/p> let str = “foo bar foo”; Answer:<\/strong><\/p> Use document.getElementById()<\/strong> to select an element by its ID.<\/p> let element = document.getElementById(“myElement”);<\/p>\n<\/div><\/div> Answer:<\/strong><\/p> Use the textContent<\/strong> property to change the text inside an HTML element.<\/p> let element = document.getElementById(“myElement”); Answer:<\/strong><\/p> Use addEventListener()<\/strong> to attach an event handler to an HTML element.<\/p> let button = document.getElementById(“myButton”); Answer:<\/strong><\/p> Event propagation refers to the order in which events are handled, including capturing, target, and bubbling phases.<\/p> Document. getElementById(“parent”).addEventListener(“click”, () => { Answer:<\/strong><\/p> Use document.createElement()<\/strong> and appendChild()<\/strong> to dynamically create and add elements to the DOM.<\/p> let newElement = document.createElement(“div”); Answer:<\/strong><\/p> Function declarations are hoisted to the top of their scope, allowing them to be called before they are defined.<\/p> console.log(greet()); \/\/ Hello<\/p>\n function greet() { Answer:<\/strong><\/p> Recursion is when a function calls itself, used to solve problems that can be broken down into similar sub-problems.<\/p> function factorial(n) { Answer:<\/strong><\/p> Closures are functions that remember the scope in which they were created, allowing them to access variables from that scope.<\/p> function outer() { Answer:<\/strong><\/p> These methods are used to change the this<\/strong> context of a function, with call()<\/strong> and apply()<\/strong> invoking the function immediately.<\/p> let obj = { num: 2 }; Answer:<\/strong><\/p> Currying transforms a function with multiple arguments into a series of functions that each take a single argument.<\/p> function add(a) { Answer:<\/strong><\/p> Wrap code that may throw errors in a try<\/strong> block, handle the error in catch<\/strong>, and optionally execute code in finally<\/strong>.<\/p> try { Answer:<\/strong><\/p> Use throw<\/strong> to create and throw a custom error based on a condition.<\/p> function checkPositive(num) { Answer:<\/strong><\/p> Common error types include SyntaxError<\/strong>,
\nconsole.log(“Hello, JavaScript!”);<\/p>\n<\/div><\/div>2. How did JavaScript evolve over time?<\/h3>
3. How do you set up a basic JavaScript development environment?<\/h3>
4. What is the difference between running JavaScript in the browser and in Node.js?<\/h3>
5. Write a simple JavaScript program that prints “Hello, World!” to the console.<\/h3>
6. How do you declare a variable in JavaScript, and what are the differences between var, let, and const?<\/h3>
\nconst age = 30;<\/p>\n<\/div><\/div>7. Explain the difference between == and === in JavaScript.<\/h3>
\nconsole.log(5 === ‘5’); \/\/ false<\/p>\n<\/div><\/div>8. How do you create an alert, prompt, and confirm dialog in JavaScript?<\/h3>
\nlet name = prompt(“What’s your name?”);
\nlet isConfirmed = confirm(“Are you sure?”);<\/p>\n<\/div><\/div>9. What are primitive data types in JavaScript?<\/h3>
\nlet isActive = true;<\/p>\n<\/div><\/div>10. Write a JavaScript program to calculate the sum of two numbers using arithmetic operators.<\/h3>
\nlet b = 10;
\nlet sum = a + b;
\nconsole.log(sum);<\/p>\n<\/div><\/div>11. How do you use an if-else statement to check if a number is positive or negative?<\/h3>
\nif (num > 0) {
\nconsole.log(“Positive”);
\n} else {
\nconsole.log(“Negative”);
\n}<\/p>\n<\/div><\/div>12. Explain the use of the switch statement in JavaScript.<\/h3>
\nswitch (day) {
\ncase 1:
\nconsole.log(“Monday”);
\nbreak;
\ncase 2:
\nconsole.log(“Tuesday”);
\nbreak;
\ndefault:
\nconsole.log(“Invalid day”);
\n}<\/p>\n<\/div><\/div>13. How do you write a for loop that prints numbers from 1 to 10?<\/h3>
\nconsole.log(i);
\n}<\/p>\n<\/div><\/div>14. What is the difference between while and do-while loops in JavaScript?<\/h3>
\ndo {
\nconsole.log(i);
\ni++;
\n} while (i <= 5);<\/p>\n<\/div><\/div>15. Write a JavaScript program to print all even numbers from 1 to 20 using a loop and the continue statement.<\/h3>
\nif (i % 2 !== 0) continue;
\nconsole.log(i);
\n}<\/p>\n<\/div><\/div>16. What is the difference between function declaration and function expression in JavaScript?<\/h3>
\nreturn “Hello!”;
\n}<\/p>\n
\nreturn “Hello!”;
\n};<\/p>\n<\/div><\/div>17. How do you use parameters and arguments in a JavaScript function?<\/h3>
\nreturn a + b;
\n}<\/p>\n18. Explain how the return statement works in a function.<\/h3>
\nreturn a * b;
\n}<\/p>\n19. What are arrow functions in JavaScript, and how do they differ from regular functions?<\/h3>
20. Write a JavaScript program using an Immediately Invoked Function Expression (IIFE).<\/h3>
\nconsole.log(“IIFE executed”);
\n})();<\/p>\n<\/div><\/div>21. How do you create an object in JavaScript, and how can you access its properties?<\/h3>
\nconsole.log(person.name); \/\/ John<\/p>\n<\/div><\/div>22. Explain the use of the this keyword in JavaScript.<\/h3>
\nname: “John”,
\ngreet: function() {
\nconsole.log(this.name);
\n}
\n};<\/p>\n23. How do you add and remove elements from an array using push, pop, shift, and unshift methods?<\/h3>
\narr.push(4); \/\/ [1, 2, 3, 4]\narr.pop(); \/\/ [1, 2, 3]\n<\/p><\/div><\/div>24. What is the difference between map() and forEach() when working with arrays?<\/h3>
\nlet doubled = arr.map(x => x * 2); \/\/ [2, 4, 6]\n<\/p><\/div><\/div>25. Write a JavaScript program to filter an array of numbers and return only the even numbers.<\/h3>
\nlet evenNumbers = numbers.filter(num => num % 2 === 0);
\nconsole.log(evenNumbers); \/\/ [2, 4, 6]\n<\/p><\/div><\/div>26. How do you find the length of a string in JavaScript?<\/h3>
\nconsole.log(str.length); \/\/ 13<\/p>\n<\/div><\/div>27. Write a JavaScript program to convert a string to uppercase.<\/h3>
\nconsole.log(str.toUpperCase()); \/\/ HELLO<\/p>\n<\/div><\/div>28. How do you extract a substring from a string using slice() and substring()?<\/h3>
\nconsole.log(str.slice(0, 5)); \/\/ Hello
\nconsole.log(str.substring(0, 5)); \/\/ Hello<\/p>\n<\/div><\/div>29. What is the use of template literals in JavaScript?<\/h3>
\nlet greeting = `Hello, ${name}!`;
\nconsole.log(greeting); \/\/ Hello, John!<\/p>\n<\/div><\/div>30. Write a JavaScript program to replace all occurrences of a substring in a string.<\/h3>
\nlet newStr = str.replace(\/foo\/g, “baz”);
\nconsole.log(newStr); \/\/ baz bar baz<\/p>\n<\/div><\/div>31. How do you select an HTML element by its ID in JavaScript?<\/h3>
32. Write a JavaScript program to change the text content of an HTML element.<\/h3>
\nelement.textContent = “New Text”;<\/p>\n<\/div><\/div>33. How do you add an event listener to an HTML element in JavaScript?<\/h3>
\nbutton.addEventListener(“click”, () => {
\nalert(“Button clicked!”);
\n});<\/p>\n<\/div><\/div>34. What is event propagation, and how does it work in JavaScript?<\/h3>
\nconsole.log(“Parent clicked”);
\n}, true); \/\/ Capturing phase<\/p>\n<\/div><\/div>35. Write a JavaScript program to dynamically create and append an HTML element.<\/h3>
\nnewElement.textContent = “Hello, World!”;
\ndocument.body.appendChild(newElement);<\/p>\n<\/div><\/div>36. Explain function hoisting in JavaScript.<\/h3>
\nreturn “Hello”;
\n}<\/p>\n<\/div><\/div>37. What is recursion, and how do you implement it in JavaScript?<\/h3>
\nreturn n <= 1 ? 1 : n * factorial(n – 1);
\n}
\nconsole.log(factorial(5)); \/\/ 120<\/p>\n<\/div><\/div>38. What are closures in JavaScript, and why are they important?<\/h3>
\nlet count = 0;
\nreturn function() {
\nreturn ++count;
\n};
\n}
\nconst increment = outer();
\nconsole.log(increment()); \/\/ 1<\/p>\n<\/div><\/div>39. How do you use bind(), call(), and apply() methods in JavaScript?<\/h3>
\nfunction multiply(a, b) {
\nreturn this.num * a * b;
\n}
\nconsole.log(multiply.call(obj, 3, 4)); \/\/ 24<\/p>\n<\/div><\/div>40. What is function currying, and how do you implement it in JavaScript?<\/h3>
\nreturn function(b) {
\nreturn a + b;
\n};
\n}
\nconsole.log(add(2)(3)); \/\/ 5<\/p>\n<\/div><\/div>41. How do you handle errors in JavaScript using try, catch, and finally?<\/h3>
\nlet result = someUndefinedFunction();
\n} catch (error) {
\nconsole.log(“An error occurred: ” + error.message);
\n} finally {
\nconsole.log(“This runs no matter what”);
\n}<\/p>\n<\/div><\/div>42. Write a JavaScript program that throws a custom error if a number is negative.<\/h3>
\nif (num < 0) {
\nthrow new Error(“Number is negative”);
\n}
\nreturn num;
\n}
\ntry {
\nconsole.log(checkPositive(-5));
\n} catch (error) {
\nconsole.log(error.message);
\n}<\/p>\n<\/div><\/div>43. What are the different types of errors in JavaScript?<\/h3>