JavaScript: A Versatile Language for the Web and Beyond
JavaScript (JS), invented by Brendan Eich in 1995, is a dominant force in web development. Initially conceived to create interactive web pages, it has evolved into a powerful language applicable to various environments.
From Web Pages to Diverse Applications
Traditionally embedded within HTML code, JavaScript scripts execute automatically when a web page loads. This capability injects dynamism into web experiences. But JavaScript’s reach extends beyond web browsers. With the advent of server-side JavaScript engines like Node.js, developers can now create real-time applications, mobile apps, online games, and more.
Beyond the Basics: Frameworks and Libraries
JavaScript frameworks and libraries, essentially collections of pre-written code, serve as valuable tools for developers. These tools provide building blocks for common functionalities, saving time and effort. They allow developers to focus on the unique aspects of their projects rather than reinventing the wheel for essential tasks.
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JavaScript Interview Questions for Freshers
1. What is JavaScript?
JavaScript is a high-level, interpreted scripting language primarily used for creating and controlling dynamic website content, such as interactive forms, animations, and other user interactions.
2.What are the different data types present in JavaScript?
JavaScript supports the following data types: Number, String, Boolean, Undefined, Null, Symbol, and Object.
3.What is the difference between let, const, and var?
var: Function-scoped or globally-scoped, can be redeclared and updated.
let: Block-scoped, can be updated but not redeclared.
const: Block-scoped, cannot be updated or redeclared.
4.Explain the concept of closures in JavaScript.
A closure is a function that retains access to its lexical scope, even when the function is executed outside that lexical scope. Closures are created whenever a function is created.
5.What is the use of this keyword in JavaScript?
The this keyword refers to the object from where it was called. Its value depends on the context in which it is used.
6.What is an Immediately Invoked Function Expression (IIFE)?
An IIFE is a function that runs as soon as it is defined. It is a design pattern used to avoid polluting the global scope.
(function() {
console.log(‘This is an IIFE’);
})();
JavaScript Interview Questions for Intermediate Level
1.What is event bubbling and event capturing in JavaScript?
Event bubbling is the propagation of an event from the target element to its parent elements. Event capturing is the opposite, where the event is captured by the parent elements first.
2.Explain hoisting in JavaScript.
Hoisting is a JavaScript mechanism where variables and function declarations are moved to the top of their containing scope during compilation, regardless of where they are declared.
3.What is the difference between == and === operators?
== is the equality operator, which performs type coercion, while === is the strict equality operator, which checks both value and type without coercion.
4.What is a promise in JavaScript?
A promise is an object representing the eventual completion or failure of an asynchronous operation. It allows asynchronous operations to be handled in a more manageable way than callbacks.
5.What are arrow functions in JavaScript?
Arrow functions are a concise way to write function expressions in JavaScript, introduced in ECMAScript 6 (ES6). They have a shorter syntax compared to traditional function expressions and do not bind their own this.
6.What is the use of the map() function in JavaScript?
The map() function is used to iterate over an array and modify its elements. It applies a provided function to each element in the array and returns a new array containing the results.
JavaScript Interview Questions for Experienced Level
1.Explain the concept of prototypal inheritance in JavaScript.
Prototypal inheritance is a way of creating objects based on existing objects, known as prototypes. In JavaScript, every object has a prototype chain, and properties and methods can be inherited from its prototype.
2.What are the different ways to handle asynchronous code in JavaScript?
Asynchronous code can be handled using callbacks, promises, and async/await syntax in modern JavaScript.
3.What is memoization and how can it be implemented in JavaScript?
Memoization is an optimization technique used to cache the results of expensive function calls and return the cached result when the same inputs occur again. It can be implemented using objects or memoization libraries like lodash.
4.Explain the concept of event delegation in JavaScript.
Event delegation is a technique where a single event listener is attached to a parent element to manage events that occur on its child elements. This improves performance and reduces memory consumption, especially for dynamically created elements.
5.What are the different ways to create objects in JavaScript?
Objects in JavaScript can be created using object literals, the new keyword with constructor functions, the Object.create() method, and ES6 classes.
6.How does JavaScript handle asynchronous programming?
JavaScript uses an event-driven, single-threaded model to handle asynchronous programming. It utilizes mechanisms such as callbacks, promises, and async/await to manage asynchronous operations without blocking the main thread.
Coding Questions
1.Write a function to find the factorial of a given number.
function factorial(n) {
  if (n === 0 || n === 1) {
   return 1;
  } else {
   return n * factorial(n - 1);
  }
}
2.Write a function to check if a string is a palindrome.
function isPalindrome(str) {
  const reversed = str.split('').reverse().join('');
  return str === reversed;
}
3.Implement a function to remove duplicates from an array.
function removeDuplicates(arr) {
  return arr.filter((value, index, self) => {
    return self.indexOf(value) === index;
  });
}
4.Write a function to reverse a string.
function reverseString(str) {
  return str.split('').reverse().join('');
}
5.Implement a function to find the largest number in an array.
function findLargest(arr) {
  return Math.max(...arr);
}