Top 25 Full Stack Developer Interview Questions and Answers

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We are going to discuss the top 25 full stack developer important questions that are most commonly asked in interviews. But before directly jumping to the interview questions, we shall have a brief introduction of a Full Stack Developer.

Who is a Full Stack Developer?

A Full-Stack developer is a person who can develop software for both the user and the service provider. In simple language, a Full-Stack developer has the knowledge of the full stack of technology that makes up a website. They are very comfortable in both front-end and back-end languages. They mostly focus on web development on both ends.

Most of the full stack developers aren’t working as full-stack developers at the beginning. They usually work in many roles before going for full-stack. They also tend to be comfortable with both business logic and user experience. In other words, they have enough knowledge of business to give advice to other people.

A Full-Stack Developer is proficient in:

  1. Server, network, and hosting environment.
  2. Relational and non-relational databases.
  3. How to interact with APIs and the external world.
  4. User interface and user experience.
  5. Quality assurance.
  6. Security concerns throughout the program.
  7. Understanding customer and business needs.
  8. HTML, CSS, and JavaScript.
  9. JavaScript frameworks like React or Angular.
  10. Programming languages like Ruby and Python.

Top 25 full stack developer interview questions

Full stack developer interview questions

Q1. What are the Success Factors for Successive Integration?

Ans – Success factors for successive integration are-

  1. Maintain a code repository
  2. Automate the build
  3. Make the build self-testing
  4. Everyone commits to the baseline every day
  5. Every commit (to baseline) should be built
  6. Try to keep the build fast
  7. Test in a clone of the production environment
  8. Make it easy to get the latest deliverables
  9. Automate deployment

Q2. Explain What is DevOps

Ans – DevOps is a newly emerging term in the IT field, which is nothing but a practice that emphasizes the collaboration and communication of both software developers and other information technology (IT) professionals. It focuses on delivering software products faster and lowering the failure rate of releases.

Q3. What is the Difference Between “Git Pull” and “Git Fetch”?

Ans – In the simplest terms, git pull does a git fetch followed by a git merge.

  • When you use pull, Git gets the message to automatically do your work for you. It is context-sensitive, so Git will merge any pulled commits into the branch you are currently working in. pull automatically merges them without giving you any chance to review it first. If you don’t manage your branches with a keen eye, you may be face to face with many problems.
  • When you fetch, Git gathers any commits from the target branch that do not exist in your current branch and stores them in your local repository. However, it does not merge them with your current branch. This is particularly useful if you need to keep your repository up to date, but are working on something that might break if you update your files. To integrate the commits into your master branch, you use merge.

Q4. What is Callback Hell?

Ans – The asynchronous function requires callbacks as a return parameter. When multiple asynchronous functions are chained together then callback hell situation comes up.

Q5. What is CORS?

Ans – CORS, abbreviation for Cross-Origin Resource Sharing, is a process used to gain the authority of different web resources on different domains. With the help of CORS, the integration of web scripts can be implemented more freely with the external content of the original domain.

Q6. What are the Differences Between ES6 and ES5 Function Constructors?

Ans – Let’s first look at an example of each:

// ES5 Function Constructor
function Person(name) { = name;

// ES6 Class
class Person {
  constructor(name) { = name;

For simple constructors, they look pretty similar.

The main difference in the constructor is observed when the effect of inheritance comes into the play. If we want to create a Student class that subclasses Person and add a studentId field, this is what we have to do in addition to the above.

// ES5 Function Constructor
function Student(name, studentId) {
  // Call constructor of superclass to initialize superclass-derived members., name);

  // Initialize subclass's own members.
  this.studentId = studentId;

Student.prototype = Object.create(Person.prototype);
Student.prototype.constructor = Student;

// ES6 Class
class Student extends Person {
  constructor(name, studentId) {
    this.studentId = studentId;

It’s much more verbose to use inheritance in ES5 and the ES6 version, here it is easier to understand and remember.

Q7. What is Multi-Threading?

Ans – The process of improving the performance of CPU is known as Multi-Threading. Usually, it is seen as the ability of a program to be managed by multiple users at a single time.

It is done by the execution of multiple processes that are supported by the operating system.

Q8. What is Continuous Integration?

Ans – Continuous Integration is the process of implementation of codes that are specially designed & automated for testing. During the time of production, it helps the developers to apply the codes simply. Web developers prefer this process for the integration of codes many times a day. Continuous Integration helps in detecting errors quickly and locating them more easily.

Q9. What are the Advantages and Disadvantages of Using “use strict“?

Ans – “use strict” is a statement that is used to enable strict mode to entire scripts or individual functions. Strict mode is a way to opt into a restricted variant of JavaScript.


  1. It makes it impossible to create global variables by mistake.
  2. Makes assignments that would otherwise silently fail to throw an exception.
  3. Makes attempts to delete undeletable properties throw (where before the attempt would simply have no effect).
  4. It is mandatory that the function parameter name should be unique.
  5. this is undefined in the global context.
  6. It catches some common coding bloopers, throwing exceptions.
  7. It stops the functioning of features that are confusing.


  1. A lot of features that most of the developers might be used to are absent.
  2. No more access to function.caller and function.arguments.
  3. The concatenation of scripts written in different strict modes might cause issues.

Q10. What do you think of AMD vs CommonJS?

Ans – Both are ways to implement a module system, which was not natively present in JavaScript until ES2015 came along. CommonJS is synchronous while AMD (Asynchronous Module Definition) is obviously asynchronous. CommonJS is designed with back-end development in mind while AMD, with its support for asynchronous loading of modules, is more intended for browsers.

In my opinion, most would find AMD syntax to be quite dull and CommonJS is closer to the style you would write import statements in other languages. Most of the time, I find AMD unnecessary, because if you served all your JavaScript into one concatenated bundle file, you wouldn’t benefit from the async loading properties. Also, CommonJS syntax is closer to the Node style of writing modules and there is less context-switching overhead when switching between client-side and server-side JavaScript development.

I’m glad that with ES2015 modules, that has support for both synchronous and asynchronous loading, we can finally just stick to one approach. Although it hasn’t been fully rolled out in browsers and in Node, we can always use transpilers to convert our code.

Q11. Explain Prototype Inheritance in Javascript

Ans – In a language implementing classical inheritance like Java, C#, or C++ you start by creating a class–a blueprint for your objects – and then you can create new objects from that class or you can extend the class, defining a new class that augments the original class.

In JavaScript you first create an object (there is no concept of class), then you can augment your own object or create new objects from it.

Every object in Javascript has a prototype. JavaScript’s inheritance system is based on prototypes, and not class-based. When a message reaches an object, JavaScript will make an attempt to find a property in that object first. If it cannot find it, then the message will be sent directly to the object’s prototype, and so on. That behavior called prototype chain or in many places, prototype inheritance.

Constructor functions are the most preferred way in JavaScript when it comes to constructing prototype chains. When we use new, JavaScript injects an implicit reference to the new object being created in the form of this keyword. It also returns this reference completely at the end of the function.

function Foo() {
  this.kind = ‘foo’

var foo = new Foo(); 
foo.kind //=> ‘foo’

Q12. When should you not use arrow functions in ES6? Name three or more cases.

Ans- Arrow functions should NOT be used:

  1. When we want function hoisting – as arrow functions are anonymous.
  2. When we want to use this/argument in a function – as arrow functions do not have this/argument of their own, they depend upon their outer context.
  3. When we want to use named function – arrow functions are anonymous.
  4. When we want to use the function as a constructor – as arrow functions do not have their own this.
  5. When we want to add function as a property in object literal and use an object in it – as we can not access this (which should be the object itself).

Q13. What is Pair-Programming?

Ans – Pair Programming is one of the core elements of extreme programming in which two developers are required to work on the same terminal. The one developer whose task is to write the code is called the “Driver” and the other who is responsible for reviewing the codes is called the “Navigator”.

Q14. What is Long Polling?

Ans – Long Polling is a pattern in the web development that is used to improve pushing data from the server to the client. By using a Long Polling pattern, the Client requests information from the server. If the server does not have any information about the client, the server holds the request and waits for some information to be available instead of sending an empty resource.

Q15. Explain a use case for Docker

Ans –

  1. Docker is a low overhead way to run virtual machines on your local box or in the cloud. Although they’re not strictly distinct machines, they give you many of those benefits.
  2. Docker can encapsulate legacy applications, allowing you to deploy them to servers that might not otherwise be easy to set up with older packages & software versions.
  3. Docker can be used to build test boxes, during your deploy process to facilitate continuous integration testing.
  4. Docker can be used to provision boxes in the cloud, and with the swarm, you can orchestrate clusters too.

Q16. What are the latest trends in Full Stack Web Development?

Ans – According to industry experts, a candidate who is passionate about full-stack development should be aware of the following trends:

  1. The rise of Vue JS Functional, real-time web apps, progressive apps, and mobile web development.
  2. Programming benefits from JavaScript improvements
  3. The emergence of more compatible extensions.

Q17. Explain the difference between REST and GraphQL

Ans – The main and most important difference between REST and GraphQL is that GraphQL does not deal with dedicated resources. Instead, everything is considered as a graph and therefore is connected and can be queried to app exact needs.

Q18. What is Event Loop?

Ans – Node.js is a single-threaded application but it supports concurrency via the concept of event and callbacks. As every API of Node js is asynchronous and being a single thread, it uses async function calls to maintain the concurrency. Node uses observer pattern. Node thread keeps an event loop and whenever any task gets completed, it fires the corresponding event which signals the event listener function to get executed.

Q19. Explain the purpose of clearing floats in CSS.

Ans – The clear CSS property specifies whether an element can be next to floating elements that precede it or must be moved down (cleared) below them. Clearing floats (or clear fixing) basically forces the containing element to expand to contain its child elements. Thus, it forces the subsequent elements to appear below it.

Q20. How can you share code between files?

Ans – This depends on the JavaScript environment.

On the client (browser environment), as long as the variables/functions are declared in the global scope (window), all scripts can refer to them. Alternatively, adopt the Asynchronous Module Definition (AMD) via RequireJS for a more modular approach.

On the server (Node.js), the common way has been to use CommonJS. Each file is treated as a module and it can export variables and functions by attaching them to the module.exports object.

ES2015 defines a module syntax which aims to replace both AMD and CommonJS. This will eventually be supported in both browser and Node environments.

Q21. What is Temporal Dead Zone in ES6?

Ans – In ES6 let and const are hoisted (like varclass and function), but there is a period between entering scope and being declared where they cannot be accessed. This period is the temporal dead zone (TDZ).


//console.log(aLet)  // would throw ReferenceError

let aLet;
console.log(aLet); // undefined
aLet = 10;
console.log(aLet); // 10

In this example, the TDZ ends when aLet is declared, rather than assigned.

Q22. What is the difference between a blue/green deployment and a rolling deployment?

Ans –

  1. In Blue/Green Deployment, you have TWO complete environments. The Blue environment is the one that is running and the Green environment is the one to which you want to upgrade. Once you swap the environment from blue to green, the traffic is directed to your new green environment. You can delete or save your old blue environment for backup until the green environment is stable.
  2. In Rolling Deployment, you have only ONE complete environment. The code is deployed in the subset of instances of the same environment and moves to another subset after completion.

Q23. What are the disadvantages of GraphQL?

Ans – Disadvantages of GraphQL are:

  1. You need to learn how to set up GraphQL. The ecosystem is still rapidly evolving so you have to keep up.
  2. You need to send the queries from the client, you can just send strings but if you want more comfort and caching you’ll use a client library -> extra code in your client
  3. You need to define the schema beforehand => extra work before you get results
  4. You need to have a GraphQL endpoint on your server => new libraries that you don’t know yet
  5. Graphql queries are more bytes than simply going to a REST endpoint
  6. The server needs to do more processing to parse the query and verify the parameters

Q24. What is Inversion of Control?

Ans – Inversion of control is a broad term but for a software developer, it’s most commonly described as a pattern used for decoupling components and layers in the system.

For example, say your application has a text editor component and you want to provide spell checking.

Your standard code would look something like this:

public class TextEditor {

    private SpellChecker checker;

    public TextEditor() {
        this.checker = new SpellChecker();

What we’ve done here creates a dependency between the TextEditor and the SpellChecker.

In an IoC scenario we would instead do something like this:

public class TextEditor {

    private IocSpellChecker checker;

    public TextEditor(IocSpellChecker checker) {
        this.checker = checker;

You have inverted control by handing the responsibility of instantiating the spell checker from the TextEditor class to the caller.

SpellChecker sc = new SpellChecker; // dependency
TextEditor textEditor = new TextEditor(sc);

Q25. What is the most loved language of a full stack developer and why?

Ans – Full Stack Developers work with a multitude of languages. Ideally, a candidate must have a few languages that he loves, preferably, some with which he can design the front end and others with which he can take care of the back end. A candidate should be able to demonstrate that well and remember to include the basic most used ones like HTML, CSS, Python, etc.

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