In simple words, we can say that Hoisting is a process in which, irrespective of where the variables and functions are declared, they are moved on top of the scope. The delete operator is used to delete the property of an object. Here, x is an object which has the property foo, and as it is a self-invoking function, we will delete the foo property from object x. After doing so, when we try to reference a deleted property foo, the result is undefined. The if condition statement evaluates using eval, so eval(function f()) returns function f() . When you use strict mode, you cannot use implicitly declared variables, or assign a value to a read-only property, or add a property to an object that is not extensible.

This may sound trivial and, in fact, it is trivial with ECMAscript 6 which introduces a new Number.isInteger() function for precisely this purpose. However, prior to ECMAScript 6, this is a bit more complicated, since no equivalent of the Number.isInteger() method is provided. The NaN property represents a value that is “not a number”. Typeof 1 will return “number” and typeof “number” will return string. The browser has an event loop which checks the event queue and processes pending events. When the onclick handler is complete, the queue is checked and the event is then handled (e.g., the onload script is executed).

Back-end Developers

Node uses “libuv” to handle its IO in a platform-agnostic way. On windows, it uses completion ports for Unix it uses epoll or kqueue, etc. So, it makes a non-blocking request, and upon a request, it queues it within the event loop which calls the JavaScript ‘callback’ on the main JavaScript thread. The type of operator is basically just the unary operator that is used before the single operand. DOM- DOM is a Document Object Model in JavaScript that helps to access document and HTML elements. When a web page is loaded the browser creates a DOM for the page.

javascript developer interview questions

It allows developers to create reusable UI components that can be used across different pages and applications. React JS works on the basis of the Virtual DOM, which allows it to update the UI efficiently without having to reload the entire page. By focusing on these metrics, developers can create high-quality React code that is easy to read, maintain, and scale over time. A component is a self-contained, reusable piece of code that can be composed using other components to create complex user interfaces.

What Are Screen Objects? State Their Various Properties.

TDZ is a behavior that occurs when a variable is accessed before it is initialized. It is a language construct that helps to catch errors as accessing data before initializing it is incorrect. When let and const keywords are used to declare variables a TDZ may occur.

  • A label and field for entering text or number will be provided.
  • Imports and exports help in writing modular code for our JavaScript applications.
  • The scope of the variable is nothing but the functionality of the variable.
  • It implies neither an object, nor a null string, nor a valid boolean, nor a number, nor an array object.
  • Undefined variables are those that are declared in the program but have no meaning.

This coding challenge is based on the classic children’s counting game used to teach about multiples. In the game, players sit in a circle counting by one, replacing each multiple of three with fizz and each multiple of five with buzz. No matter how well a candidate answers questions about JavaScript, you’ll ultimately want to see them put their knowledge into action by doing some actual coding. Here are some coding challenges you can use to gauge how an applicant handles coding problems. Demonstrates an understanding of different types of web development. When interviewing JavaScript Developers, the most suitable candidates will demonstrate key knowledge of JavaScript, drive, and excellent communication skills.

List Some Key Features of JavaScript.

Variables that are not declared or that do not exist in a program or application. This file exports two functions that calculate the squares and diagonal of the input respectively. A callback is a JavaScript function that is passed to another function as an argument or a parameter. This function is to be executed whenever the function that it is passed to gets executed. Variable names cannot be similar to that of reserved keywords. Java source code needs a compiler before it can be ready to run in realtime.

javascript developer interview questions

This whole optimization process significantly reduces the web application load time, thereby making it more efficient. Virtual DOM plays a significant role in the scope of React development. It is important for a good candidate to be able to describe why it is useful to solve DOM manipulation problems with virtual DOM. From a React developer’s perspective, both GraphQL and REST are viable options for building APIs, but they have some differences that can affect the development process.

How to make an array empty?

Therefore, when anything is done to arr2 (i.e., when we invoke arr2.push;), arr1 will be affected as well since arr1 and arr2 are simply references to the same object. When a function is invoked, JavaScript does not require the number of arguments to match the number of arguments in the function definition. If the number of arguments passed exceeds the number of arguments in the function definition, the excess arguments will simply be ignored.