JavaScript Interview Questions

JavaScript Interview Questions For Freshers

Let us start with JavaScript questions that are suited for young graduates and freshers in the domain with little to no work experience:

Debugger is a JavaScript component developers activate to debug their code. Systems may have in-built debuggers that can be turned on and off at the right time, requiring developers to report faults. Under such a situation, the code’s remaining section should stop execution before getting to the next line while debugging.

In JavaScript, both of these operators are comparison operators. While the “==” operator is used for comparing values, the “===” operator is used to compare values and types.

In JavaScript, the “var” keyword is used from the beginning, while the “let” keyword was added much later in 2015. The “var” keyword holds a function scope. The variable you specify anywhere in the function using “var” is accessible. On the other hand, a variable scope declared with the “let” keyword is limited to the block where it is declared.

JavaScript is a dynamically typed programming language for building web applications. Here, developers check the type of a variable during run-time. On the other hand, the type of a variable in a statically typed language is checked during compile-time. Being a dynamically typed language, the variables in JavaScript are not related to any type, making them hold values of any data type.

The strict mode is a new feature launched in ECMAScript 5 that allows developers to write a function or a code in a strict operational environment. Mostly, the programming language is not too “severe” with regard to throwing errors. However, in the strict mode, all error forms (including silent errors) are thrown. This makes debugging a lot simpler for developers.

Here are some of the most important characteristics of the strict mode in JavaScript:

  • It does not allow duplicate arguments by developers
  • The strict mode does not allow developers to use the JavaScript keyword as a function name or parameter
  • Developers use the “use strict” keyword for defining the strict mode at the beginning of the script
  • All browsers support the strict mode in JavaScript
  • Developers cannot create global variables in the strict mode

In JavaScript, self-invoking functions are the functions where self-invoking expressions are automatically invoked without being requested. A function expression will execute automatically if it is followed by (). It is also important to note that a function declaration is not capable of being invoked by itself.

Generally, a JavaScript developer declares and calls a function. However, they may use anonymous functions to automatically run a function when it is described. It is not called again and these functions have no names.

Advanced JavaScript Interview Questions

Let us now move on to advanced JavaScript interview questions suited for experienced professionals with sufficient work experience in the domain:

Arrow functions are the JavaScript functions launched in the programming language’s ES6 version. They provide users with a newer and shorter syntax to improve declaring functions. Developers can use these functions only as a function expression.

Arroe functions can be declared without the function keyword. In the case of a single returning expression, there is no need to use the return keyword in an arrow function. Moreover, you can remove the {{ '{ }' }} braces in the case of functions having a single line of code.

In JavaScript, the prototype design pattern is used to produce different objects. Instead of returning uninitialized objects, the design pattern creates objects with values replicated from a template - or sample - object.

A good example of prototype patterns in JavaScript coming in handy is the introduction of business objects with parameters. Here, the new business object’s default settings are stored in the concerned prototype object. The prototype design pattern is rarely used in traditional programming languages. However, it is used to create new objects and templates in JavaScript as it is a prototypical language.

Here are the different methods used to declare or construct a JavaScript object:

  • Using className
  • Create method
  • Object literals
  • Using function
  • With object constructor

In JavaScript, promises are used by developers to handle asynchronous operations. Before the introduction of promises, developers used callbacks for this function. However, the limited functionality of callbacks often led to unmanageable code if multiple callbacks are used..

A JavaScript promise has four different states:

  • Pending - This is the first state of a JavaScript promise, representing that it is neither fulfilled nor rejected.
  • Fulfilled - This state implies that a promise has been fulfilled, i.e., the asynchronous operation is completed.
  • Rejected - The rejected state implies that a promise has been rejected due to a specific reason. Here, the asynchronous operation has failed.
  • Settled - This state represents a promise either being fulfilled or getting rejected.

Frequently Asked Questions

Why are JavaScript developers still in demand?

Over time, JavaScript has stayed in tune with the ongoing tech trends in the industry. Since its launch in 1995, the programming language has made responsive design easier. It gives internet users a seamless experience through an interactive user experience.

What is the salary of JavaScript developers in India?

The salary of a JavaScript developer in India can range from ₹2 lacs to ₹12 lacs, making the average annual salary around ₹4.5 lacs. This package can increase for experienced professionals who choose to upskill themselves.

Which popular companies use JavaScript to build their web applications?

Here are some of the most popular companies that use JavaScript to build their web applications:

  • Facebook
  • Microsoft
  • Google
  • PayPal
  • LinkedIn
  • Uber
  • Netflix
  • Groupon

Will becoming a JavaScript developer make my career future-proof?

JavaScript has stayed relevant for organizations and developers for almost three decades and it is likely to continue its prominence in the industry. If you stay in sync with the current industry trends and upskill yourself, securing a job as a JavaScript developer can future-proof your career. Companies will always need skilled developers for their web applications and you will always be of immense value to them.

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