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Advanced Javascript Interview Questions

March 15, 2022

What are the most frequently asked advanced JavaScript interview questions?

JavaScript is a dynamic, interpreted programming language that lets you implement complex features on web pages.

Indeed, it’s a programming language which is considered one of the core technologies of the “world wide web” along with HTML and CSS. More than 97% of websites use client-side JavaScript for web pages that contain third-party libraries.

In this blog post, we have listed advanced JavaScript interview questions and answers to help you prepare for your JavaScript interview! ?

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10+ Advanced JavaScript Interview Questions and Answers

1. What is functional programming?

Functional programming is a programming paradigm that connects everything as a mathematical function.

First of all, functions are fundamental to the coding organization; they are found in all higher-order programming languages. Since the 1950s, functions have been used to create programming languages, including Lisp, Haskell, Clojure, and Machine Learning.

Overall, functional programming makes the most of its functions to create clean and maintainable applications.

2. What are the benefits of event delegation in JavaScript?

JavaScript has great features that make it better than other programming languages and the delegation model is one of them.

Moreover, JavaScript events are at the core of all interactions on web pages.
It’s a simple technique where a single event handler is added to a parent without having to add event handlers to multiple children.

Instead of adding an event listener to each similar item, an event can be called on a specific target by adding an event listener to a parent and using the event object’s target property.

3. How do you calculate Fibonacci numbers in JavaScript?

Fibonacci numbers/sequence is a sequence of numbers calculated by adding the values of the previous two numbers. It is also known as the golden ratio.

The first seven values are 0, 1, 1, 2, 3, 5, 8.
This JavaScript function will return the Fibonacci numbers sequence up to a given number of terms.

Here is an example of extracting the Fibonacci series to desired numbers using a for loop in JavaScript.

4. What are cookies, and how are they created and read in JavaScript?

Cookies are small text files stored on a computer and are developed when a user goes to websites to store some information they need.
Examples are username details and information about shopping cart content from previous visits.

Additionally, the data contained in the cookie is automatically transmitted between the web browser and the web server so that the script on the server can read and write the values stored on the client. Therefore, JavaScript can also replace cookies using the cookie property of the Document object.

5. What is the role of deferred scripts in JavaScript?

Defer is the ‘boolean’ value used to indicate that the script is executed after the documents have been parsed.

Importantly, it only works with external scripts and reports that the script will not create a context. That way, the browser can continue to parse the rest of the page. The <script> with the defer attribute does not block the page.

To sum it up, Async allows scripts to be executed asynchronously as soon as they are downloaded. However, Defer allows execution only after the entire document has been parsed.

advanced javascript interview questions

6. What is the purpose of wrapping whole JavaScript files in anonymous functions?

Wrapping is a popular method in JavaScript libraries that you can use as a developer.

The purpose of wrapping is to create a namespace and control the visibility of member functions, for instance. Moreover, it wraps the code in a function scope and reduces conflict with other libraries. This is referred to as an Instantly Invoked Function Expression (IIFE) or Self-Executing Anonymous Function.

7. What is a generator function?

A generator function is defined as a regular function but does so with the yield keyword instead of return when it needs to produce a value.

Furthermore, with ECMAScript 2015, generators were introduced in the JavaScript language.

A generator is a process that can be paused and resumed and can return multiple values.

Moreover, generators can maintain state and can be used to implement infinite scrolling on the front end of a web application, working on sound wave data.

Overall, advantages of generators: lazy evaluation, memory efficiency, caveats.

8. When should one use Arrow functions in ES6?

Arrow functions aim to solve the problem where we need to access its property within a callback. For instance, there are several ways to do this. First, assign it to a variable, use binding, or use the third argument found in Array collection methods. Still, arrows seem to be the most straightforward workaround.

When should the arrow function be used?
Generally, the arrow function syntax can be used with our array-related method, like map(), reduce(), filter().
Also, it can be easily read and understood with arrow function syntax instead of normal function syntax.

Advantages of using the arrow function:
Arrow functions significantly reduce a lot of code and make the mod more readable.
The syntax automatically links “this” to the context of the surrounding code.
Ok => typing is more flexible compared to typing function keyword.

9. What is hoisting in JavaScript?

Hoisting is JavaScript’s default behavior to move notifications to the top of container scopes. Additionally, when JavaScript code is interpreted, the interpreter invisibly moves all variable and function declarations to the top of the scope in which they are declared, called hoisting. More, it also allows functions to be used safely in code before they are declared.

10. In Javascript, why is “this” operator inconsistent?

(Considering this blog post, Node.js running on the server side is considered out of scope.)

In JavaScript, the “this” operator can refer to different operations under different scenarios. It typically refers to the object present in a method within a JavaScript “object”. But when used as a callback, it becomes a reference to the calling object.

It has different values ​​depending on where it is used.

1. In a method this refers to the owner object.
Here the Student object is the owner of the fullName method.

2. When used alone, the owner is the Global object.
var x = this
>>> console.log(this)[Object Window]

3. In a JS function, the owner of the function is the default binding for it.

4. In any case, this refers to the element that received the event.

5. Methods like call() and application() can redirect this to any object.

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