Real interview questions from BharatPe company. Includes theoretical concepts and coding problems.
What are the key features of JavaScript and how is it used in web development?
JavaScript is a high-level, dynamic, and interpreted programming language that is primarily used for client-side scripting on the web. Its key features include first-class functions, closures, and the ability to create interactive web pages. JavaScript is used in web development to create dynamic and interactive web pages, web applications, and mobile applications.
What is the difference between null and undefined in JavaScript?
In JavaScript, null and undefined are two distinct primitive values that are often confused with each other. Null represents the absence of a value, whereas undefined represents an uninitialized or non-existent variable. Null is a primitive value that can be assigned to a variable, whereas undefined is a type that represents an uninitialized variable.
What is a closure in JavaScript and how is it used?
A closure in JavaScript is a function that has access to its outer scope's variables, even when the outer function has returned. Closures are used to create private variables and functions, and to encapsulate data and behavior. They are also used to create higher-order functions, which are functions that take other functions as arguments or return functions as output.
What is the difference between a for loop and a while loop in JavaScript?
In JavaScript, a for loop is used to iterate over a block of code repeatedly for a specified number of times, whereas a while loop is used to iterate over a block of code repeatedly while a certain condition is true. A for loop is typically used when the number of iterations is known, whereas a while loop is used when the number of iterations is unknown.
What is a callback function in JavaScript and how is it used?
A callback function in JavaScript is a function that is passed as an argument to another function, and is executed by that function. Callback functions are used to handle asynchronous operations, such as reading data from a file or making an HTTP request. They are also used to create higher-order functions, which are functions that take other functions as arguments or return functions as output.
What is the difference between synchronous and asynchronous programming in JavaScript?
In JavaScript, synchronous programming refers to the execution of code in a sequential manner, where each statement is executed one after the other. Asynchronous programming, on the other hand, refers to the execution of code in a non-sequential manner, where multiple statements can be executed concurrently. Asynchronous programming is used to handle tasks that take a long time to complete, such as reading data from a file or making an HTTP request.
What is a promise in JavaScript and how is it used?
A promise in JavaScript is an object that represents the eventual completion of an asynchronous operation, and its resulting value. Promises are used to handle asynchronous operations, such as reading data from a file or making an HTTP request. They provide a way to handle the result of an asynchronous operation, and to handle any errors that may occur during the operation.
What is the difference between a map and a filter in JavaScript?
In JavaScript, a map is a function that applies a given function to each element of an array, and returns a new array with the results. A filter, on the other hand, is a function that applies a given function to each element of an array, and returns a new array with only the elements that pass the test. Maps are used to transform data, whereas filters are used to select a subset of data.
What is a reducer in JavaScript and how is it used?
A reducer in JavaScript is a function that takes an accumulator and a value, and returns a new accumulator. Reducers are used to reduce an array to a single value, such as summing up all the elements of an array. They are also used to flatten an array of arrays, and to group an array of objects by a common key.
What is the difference between a class and an object in JavaScript?
In JavaScript, a class is a blueprint for creating objects, and defines the properties and methods of an object. An object, on the other hand, is an instance of a class, and has its own set of properties and methods. Classes are used to define the structure and behavior of an object, whereas objects are used to represent real-world entities and to encapsulate data and behavior.
What is inheritance in JavaScript and how is it used?
In JavaScript, inheritance is a mechanism by which one class can inherit the properties and methods of another class. Inheritance is used to create a hierarchy of classes, where a subclass inherits the properties and methods of a superclass. Inheritance is used to promote code reuse and to create a more modular and maintainable codebase.
What is polymorphism in JavaScript and how is it used?
In JavaScript, polymorphism is the ability of an object to take on multiple forms, depending on the context in which it is used. Polymorphism is used to create more flexible and generic code, and to promote code reuse. Polymorphism can be achieved through method overriding, method overloading, and function polymorphism.
Write a JavaScript function to find the maximum value in an array of numbers.
function reverseString(str) {
return str.split('').reverse().join('');
}
Write a JavaScript function to find the first duplicate in an array of numbers.
functionfindFirstDuplicate(arr) {
var seen = {};
for (var i = 0; i < arr.length; i++) {
if (seen[arr[i]]) {
return arr[i];
}
seen[arr[i]] = true;
}
returnnull;
}
Write a JavaScript function to find the minimum value in an array of numbers.
