Ace your next JavaScript Interview with these 7 Common Questions and Answers 💻
Tags: webdev, javascript, beginners, programming
Published: 2023-01-25 17:53:25

In this article, I will cover the most common questions you may encounter during **a JavaScript interview**, providing detailed answers and examples to help you stand out from the competition. Whether you are a beginner or an experienced developer, this guide will give you the confidence you need **to impress your interviewer and land the job**.

### 1️⃣ What is JavaScript, and how is it different from Java? 🤔
![What is JavaScript, and how is it different from Java?](https://cdn-images-1.medium.com/max/800/0*l8XyU1op_VOjizrO)

JavaScript and Java are both programming languages, but they are used for different purposes and have some key differences.

JavaScript is a scripting language primarily used to **create interactive and dynamic websites.** At the same time, Java is a general-purpose programming language that can be used to create a wide range of applications, including mobile and desktop apps, web applications, and backend systems.

**The browser executes JavaScript code**, while Java code is typically compiled and executed on a virtual machine or a specific device.


### 2️⃣ What is the difference between let and var?

![What is the difference between let and var?](https://cdn-images-1.medium.com/max/800/0*FPRsBD44FSekX1ln)

`var` and `let` are used to declare variables in JavaScript, but they have some key differences in terms of hoisting and scoping. `var` variables are hoisted to the top of their scope and are accessible throughout the entire scope. `let` variables, on the other hand, are **only accessible** within the block they were declared in and do not get hoisted

{% embed https://gist.github.com/NauCode/e9fef17140782fa4c4443d79dcb2cd23 %}


### 3️⃣ What is the difference between == and ===?

`==` and `===` are used for equality comparison in JavaScript, but they behave differently regarding type coercion. `==` compares values after type coercion, while `=== **compares values without type coercion**.

{% embed https://gist.github.com/NauCode/4fcedffd7548ec4195a76f6925f85ec7 %}

It's generally recommended to use `===` in most cases **to avoid unexpected behavior** due to type coercion.


### 4️⃣ What is closure in JavaScript?

A closure in JavaScript is a function that **has access to the variables in its parent scope**, even after the parent function has returned.

{% embed https://gist.github.com/NauCode/e50c1c4c607c52da76ac620471c53664 %}

In this example, the innerFunction has access to the variable x from its parent scope, the outerFunction.


### 5️⃣ What is the difference between call and apply?

![What is the difference between call and apply?](https://cdn-images-1.medium.com/max/800/0*HXZ-avr3WO2x_KTs)

Both `call` and `apply` **are used to call a function** and set the value of `this` inside the function, but they have different syntaxes. `call` takes in the value of `this` as the first argument, followed by any additional arguments for the function.

{% embed https://gist.github.com/NauCode/1db71ff3db36d33c3bcb10d381d9671f %}

`apply` also takes in the value of `this` as the first argument, but **it expects the additional arguments for the function to be passed in as an array**.

{% embed https://gist.github.com/NauCode/dc5d53ec3bef30987343d91d4d11ae3a %}


### 6️⃣ What is an event loop in JavaScript?

JavaScript uses an event loop to handle concurrency and handle events as they occur. The event loop constantly checks the message queue and the call stack. When a function is called, i**t is added to the call stack and executed**.

If any events in the message queue need to be handled, they are added to the call stack and executed. This allows JavaScript to **handle multiple events and function calls simultaneously** without freezing the main thread.


### 7️⃣ What is the difference between synchronous and asynchronous code?

Synchronous code is **executed line by line**, and the following line of code can't be executed until the current line is finished.

Asynchronous code, on the other hand, **allows for multiple operations to occur at the same time**. In JavaScript, this can be achieved through callbacks or promises.

{% embed https://gist.github.com/NauCode/e624f579e057123756076fb5913c5232 %}

In the asynchronous example, the for loop is executed after the "*Moving on...*" message is logged, allowing other code to continue executing.

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You have made it to the end of this guide and are now well-equipped with the knowledge and tools **necessary to ace your next JavaScript interview**. Remember to practice, stay up to date with the latest features and best practices, and, most importantly, **be confident.** I believe in you and know you will knock your interview out of the park. Good luck! 🍀


### 🌎 Let's Connect!

-   My [Twitter: @thenaubit](https://twitter.com/thenaubit)
-   [My Substack](https://coderpreneurs.substack.com/)