Full Stack Software Developer Interview Questions: A Comprehensive Guide to Landing Your Dream Job

Advanced senior full-stack developer interview questions and answers

How would you debounce a function in JavaScript?

Debouncing means that a function won’t run until a certain amount of time has passed since the last event that made it happen. Heres one way of creating a debounce function in JavaScript:

How do you handle error handling in a GraphQL server?

You can handle errors in a GraphQL server by creating your own error format, adding error codes, and enclosing resolver functions with middleware or higher-order functions that catch errors. Errors should be properly labeled and sent back to the client in a structured way to make handling errors easier on the client side.

How would you implement a recursive function to calculate Fibonacci numbers in JavaScript?

A recursive function to calculate Fibonacci numbers can be implemented as follows:

Note: This solution is inefficient due to repeated calculations.You need to use dynamic programming for better performance.

What are JavaScript generators? Can you provide an example?

Generators are special functions in JavaScript that let you make an iterator and use the yield keyword to move through it. Heres an example:

In React, explain the process of a components lifecycle and the associated lifecycle methods.

A React component goes through three main phases in its lifecycle: mounting, updating, and unmounting. In each phase, there are associated lifecycle methods. These methods can be used to manage state and side effects in a components lifecycle:

Mounting: constructor, getDerivedStateFromProps, render, componentDidMount.

Updating: getDerivedStateFromProps, shouldComponentUpdate, render, getSnapshotBeforeUpdate, componentDidUpdate.

Unmounting: componentWillUnmount.

What is the difference between controlled and uncontrolled components in React?

The state of a controlled component changes the form input values through event handlers. On the other hand, the input state of an uncontrolled component is managed by the DOM. Controlled components make sure that inputs are valid, that their states are updated, and that they are in sync with the state of other components. On the other hand, uncontrolled components may be used if the DOM input state management is enough for simple inputs.

Can you provide a brief example of useMemo and useCallback hooks in React?

useMemo returns a memoized value, preventing unnecessary calculations if the inputs dont change. The useCallback method saves a function so that it doesn’t have to be defined again and again on each render. This can be useful when sending callbacks to child components.

Heres an example:

How would you implement a simple Express.js middleware function to log incoming requests?

Heres a simple example of a middleware function in Express.js that logs incoming requests:

How would you implement a simple pub/sub pattern in JavaScript?

A simple pub/sub system can be achieved with an event emitter:

In the context of Node.js, what is the purpose of Event objects in modules like http or fs?

Event objects are used by Node. js modules to emit events to signal state changes, resource availability, or errors. Event-driven programming using Event objects allows for efficient and highly scalable applications, especially when dealing with I/O-bound workloads.

Can you provide an example of using the async/await syntax for handling asynchronous file I/O with Node.js?

Heres a simple example of reading a file asynchronously using async/await and the fs.promises API:

How would you implement a cache for a RESTful API in Express.js?

Middleware and an in-memory JavaScript object can be used to make a simple caching system. Redis and other more advanced caching systems are also available. Heres an example with an in-memory cache:

How can you create a custom Pipe in Angular, and where can it be used?

In Angular, you can make your own Pipe by defining a class that implements the PipeTransform interface and decorating it with @Pipe(). Pipes can be used to transform values in Angular templates within data bindings. Heres an example of a custom “multiply” pipe:

How do you handle state management in large Vue.js applications?

For large Vue. js applications, it is recommended to use Vuex, a centralized state management library. Vuex gives you a single source of truth for the state of an application and lets you make atomic, predictable changes to the state using actions, mutations, and getters.

How would you implement a middleware function in a Koa.js server to measure request processing time?

Heres an example Koa.js middleware function to measure request processing time:

Explain the reactive programming paradigm and its advantages for web development.

By using data streams, like events or changes in variables, and responding to them, reactive programming is a way of writing code. It lets you program in an asynchronous, event-driven way and can help you make web apps that are fast, reliable, and can respond automatically to changes in state. Reactive programming can enhance code maintainability, expressiveness, and simplify complex asynchronous scenarios.

Can you provide a brief example of RxJS observable, including creation and subscription handling?

Heres an example of creating and subscribing to an RxJS observable, which emits a new value every second:

In a Python web application, how can you implement message passing between the server and a WebSocket client?

You can use a library like Flask-SocketIO or Django Channels in a Python web app to set up WebSocket communication and handle message passing between the server and the WebSocket client. The server and client send and receive messages via the WebSocket using event-based listeners and emitters.

Can you provide an example of how to use CSS Grid Layout?

Heres a simple example of a CSS Grid Layout:

How would you handle optimistic updates in a web application?

When optimistic updates are used, the client-side state and UI are changed right away to reflect a user action, assuming the server request will be successful. If the server request fails, the previous state is restored, and the user is notified about the error. Heres how to handle optimistic updates in a web application:

• Capture the current state before performing an update.
• Update the client-side state and UI immediately.
• Send the update request to the server.
• If the server request goes through, confirm the update and keep the client-side state the same.
• If the server request fails, go back to the previous state and let the user know about the problem.

For state management, this method can be used with tools like Redux or Vuex, and it can make the application seem faster and more responsive.

How would you implement error boundaries in a React application?

Error boundaries are a mechanism provided by React to catch and handle errors in the component tree. To set an error boundary, make a component that supports the static getDerivedStateFromError or the componentDidCatch lifecycle method and wrap it around the components you want to use. Heres an example:

What is request blocking in web performance optimization and how can it be addressed?

Request blocking occurs when the browser is forced to wait for a resource (e. g. (a script, a stylesheet, or a font) needs to be fetched and processed before it can continue to render the DOM or run more scripts. To address request blocking:

• Async or defer attributes on script tags let scripts download and run without stopping rendering.
• To avoid blocking, load CSS stylesheets using the media attribute or JavaScript.
• Custom web fonts that block rendering should be used as little as possible, or the font-display property can be used to control how they load.
• Use smart ways to load resources, like loading important resources first and non-important resources slowly.

Can you explain the concept of atomic design in modern web design?

Atomic design is a way to make design systems by dividing the user interface into five levels of components that are arranged in a hierarchy:

• Atoms are simple building blocks that can be HTML tags, buttons, inputs, labels, or inputs.
• Molecules are groups of atoms that work together to make a simple unit, like a search form.
• Organisms are made up of molecules and/or atoms that are put together to make a more complex, reusable part of the interface, like a header or sidebar.
• Templates are layouts that put organisms and other UI elements together to make a page structure.
• Pages: Examples of templates that have real content added to them to show what the final design will look like

This method allows for a systematic, modular, and scalable approach to web design and development.

How would you implement a performance benchmarking tool for Node.js applications?

To implement a performance benchmarking tool for Node. js applications, you can use built-in modules like perf_hooks or third-party libraries like Benchmark. js. These tools help you find out how long certain functions or pieces of code take to run and give you information about how your code works.

Heres an example using perf_hooks:

Intermediate senior full-stack developer interview questions and answers

What is an application server, and how does it work?

An application server is a specialized software that provides a runtime environment and middleware for running enterprise-level applications. It handles the communication between the user interface, application logic, and data storage layers of an application. It provides the business logic behind any application.

The client asks the web server for something, and the web server sends it to the application server. The application server requests the information from the database server and sends it back to the web server. The web server sends the information to the client.

How do you optimize SQL queries?

Optimizing SQL queries means identifying the most effective techniques to enhance SQL query performance. Here are the most effective ways to optimize queries.

Indexing: It helps in accessing the database quickly to find the relevant data.

Use SELECT query instead of SELECT*: Instead of using SELECT* to find the columns you need, use SELECT query to do so. This will keep the query from having to do extra I/O operations that slow it down.

Don’t use too many JOINs. Make sure you use the right JOIN type for your SQL query to get the results you want and avoid extra work.

Use subqueries: Using a subquery instead of a JOIN can be more efficient sometimes. A subquery may be faster than a JOIN if all you need to do is get data from one table based on data from another.

Use table aliases: Table aliases can make your query easier to read and write. Use aliases for tables and columns to make your query more readable.

Optimize database design: Optimize database design by avoiding redundant data and using appropriate data types. A well-designed database can help you improve query performance.

Use Wildcards: Using wildcards helps you search the database for matching results.

How do you handle browser compatibility issues?

Browsers like Google Chrome, Mozilla Firefox, Safari, Microsoft Edge, etc. , may interpret web code differently. Because of this, a website or app that works fine in one browser might not work the same way in another. Here are a few tips to handle browser compatibility issues.

Use a CSS Reset: Different browsers have different design layouts, which can cause layout inconsistencies. A CSS reset can help by setting a common baseline for all browsers.

Cross-browser frameworks and libraries, like jQuery, React, or Angular, can help developers avoid writing code that only works in one browser and give users a consistent experience across all of them.

Test on different devices and browsers: To make sure their websites and apps work on all of them, developers should test them on a number of different browsers, including popular ones like Chrome, Firefox, Safari, and Edge.

Use polyfills and shims. Polyfills and shims are pieces of code that provide fallback functionality for web features that some browsers don’t support. You can use libraries like Modernizr, Polyfill. io, or HTML5 Shiv to help fill in gaps in browser support.

What is the difference between abstract and interface?

• An interface can only have abstract methods, but an abstract class can have both types of methods.
• Variables declared in a Java interface are only static and final, but variables declared in an abstract class can have both types of variables.
• An abstract class can provide an implementation of an interface. An Interface, on the other hand, can’t use an abstract class.
• In Java, an abstract class can have members that are public, private, or protected. But, an interface only has members that are public.
• An abstract class can be extended using the “extends” keyword. An interface can be implemented using the “implements” keyword.

Why and how do you clear floats in CSS?

With floats in CSS, you can place elements (usually s) so that the content around them can flow around them. But when you use floats, it may cause elements that come after them to flow around the floated items, which can cause layout problems you don’t want. Clearing floats is necessary to prevent such issues and ensure proper control of the layout.

There are multiple methods to clear floats in CSS. Some common techniques include:

• The clear CSS property can be set to left, right, both, or none for the elements that come after the floated elements.

clear: both;

• Clearfix (the most common method): To get rid of the floats, use the “clearfix” technique with a pseudo-element, which means making an invisible element. This method helps avoid adding extra markup to your HTML:

.group::after {

content: “”;

display: table;

clear: both;

What are the main differences between process and thread?

How do you share code between files in JavaScript?

JavaScript allows us to share code between files by ‘imports’ and ‘exports’. We can share code written in one file with another using ‘require’ and ‘module. exports’ statements in ES5 syntax, whereas we can use ‘import’ and ‘export’ statements in ES6 syntax.

What is the difference between Host objects and Native objects?

Native objects are pre-defined objects provided by JavaScript. These objects are available to all users globally, irrespective of the machine and environment.

On the other hand, host objects are environment-specific JavaScript objects, varying according to the machine environment we use.

What is the best way to remove array duplicates in ES6?

In ES6, the best way to get rid of duplicates in an array is to use a set, which can only hold unique values. When you convert the array to a set, it will remove any duplicate values. Then you need to convert the set back to an array with unique values.

What is “Strict Mode,” and how to use it in JavaScript?

Strict mode is a feature in JavaScript that allows us to execute the code in a restricted environment. It helps detect errors in the code that would normally get executed without any errors. We can turn on strict mode by putting “use strict” at the beginning of the file or in the function that needs it. Example:

The string “use strict” at the beginning of the file tells the JavaScript interpreter to run the code in strict mode, which has stricter rules for syntax and how to handle errors. Next, we create a function called myFunction() that takes an unknown variable x, multiplies it by 2, and returns the result. Nothing would go wrong with this in non-strict mode, but an error will be raised because x is not declared in strict mode.

How does database indexing work?

Database indexing is like indexing in a book. An index in a book helps us quickly find a certain chapter or piece of information. Similarly, an index in a database helps us quickly find the data. When you run a query with a “where” clause, it cuts down on the number of rows or columns that need to be checked and quickly finds the data you need. Thats how database indexing works.

What are filters in Vue.js?

A filter is a JavaScript function that allows you to apply common text formatting to dynamic data. It doesnt change the data directly but only changes the output to a browser. It takes through value, manipulates it, and displays the processed values.

Filters are applied using the “pipe character (|) followed by the filter name. We can apply filters in two ways: local and global. Local filters can only be used in the component where they were defined. Global filters, on the other hand, can be used in any component.

Why is “this” operator inconsistent in JavaScript?

When used in different places, the “this” operator in JavaScript can take on different values, which can seem strange. Its value is determined by how the function used is called rather than where it is declared. The call, apply, and bind functions can also change the value of “this.” This makes it hard to know what the value of “this” will be in a given situation, which leads to errors.

What is Data Structure, and what are the different types?

A data structure is a way to store and organize data (numbers and facts) in a way that makes it easy to find when you need it. Basically, there are two types of data structures:

Linear data structure:

• Array: A linear collection of elements of the same type.
• Stack: Items are kept according to the LIFO (last-in, first-out) rule.
• As the saying goes, “first-in, first-out” (FIFO). This is how queues work.
• A linked list is a group of items where each one has a link to the next item in the list.

Non-linear data structure:

• A graph is a type of data structure made up of points (vertices) and lines (edges) that connect those points.
• Trees are a type of hierarchical data structure where each node has two child nodes.

What is the purpose of the main element in HTML?

The main element in HTML represents the core content of a document. Sidebars, navigation links, search forms, and other things that are used more than once in different documents should not have the same content in the tag. The element must be used only once in the HTML file. It requires a closing tag at the end of the content.

What are semantic HTML tags, and why should you use them?

HTML that adds meaning to a webpage instead of just making it look good is called semantic HTML or semantic markup. For example, HTML elements such as header, footer, nav, main, article, p time, etc. , are used to define the different sections and content on the page.

There are several reasons for using semantic HTML:

• It helps search engines figure out how important and relevant a web page is.
• The code is easier to understand in semantic HTML, which makes it easier to keep up with a website.
• It’s easier to use and read pages that have semantic elements added to them.
• Semantic HTML is important for search engine optimization (SEO).

What is Pascal String?

In some programming languages, like Pascal, a Pascal string is a type of data structure that is used to store and change text strings. It might not be as common in full-stack development as some other string representation methods, but you can still come across it or use it in some situations.

Common types of Pascal strings are

Character arrays: These are numbers, letters, special characters, etc., enclosed in a single quote.

String variables: The variable of string type is declared inside the var block in Turbo Pascal.

Short strings: We use this string type when the total capacity remains constant.

Null terminated strings: This string type has the same structural layout as a C string.

AnsiStrings: This string type does not have any length limit.

What is the difference between Map and WeakMap?

• Any kind of value can be put into a map, such as a string, boolean, number, etc. , whereas a WeakMap only accepts only objects as keys.
• Maps are iterable, but WeakMaps are not.
• The size of a “Map” is known, but not the size of a “WeakMap.”
• There is no key pointer removal from “Map” by the garbage collector. However, the key pointer removal from “WeakMap” does happen.

What is the main difference between a web server and an application server?

• On the other hand, an application server handles dynamic content and provides business logic and application functionality to clients. A web server handles HTTP requests and provides web browsers with static content like HTML pages, s, and other files.
• Most of the time, an application server is put in front of a web server. The web server handles incoming web requests and serves static content, while the application server handles dynamic requests and runs business logic.
• It is the job of web servers to run websites and web applications, while the job of application servers is to run enterprise applications.
• Multiple threads are not supported by web servers, but they are supported by application servers.

What is the difference between JDBC and Hibernate?

JDBC and Hibernate are Java technologies used for managing relational databases. Both technologies have some similarities, but they are not the same. Here is the difference between JDBC and Hibernate.

How does DevOps work?

DevOps is a technique that aims to build coordination to streamline software development and IT operations. It enables teams to work together to deliver software products faster and ensure better quality. The primary goal of DevOps is to increase efficiency and reduce errors.

Under a DevOps model, the development and operations teams are no longer “siloed. ” Sometimes, the two teams are merged into a single team. The DevOps engineers work across the complete application lifecycle – from development and testing to deployment and operations. These engineers have multidisciplinary skills.

What is the main difference between Promises and async/await in JavaScript?

Promises provide an interface for dealing with asynchronous operations, allowing chaining of . then() and . catch() methods. With the help of async functions and the await keyword, async/await adds a little sugar to Promises to make asynchronous code look more like synchronous code.

A thread is defined as the single, sequential flow of the control within a program. It is not the program itself and cannot run on its own. In a running program, a thread may have to dig some of its resources.

For example, the execution stack and program counter must belong to that thread. The code in a given thread is useful only for that particular context. A single thread has a single point of execution, i. e. , only one user can manage one request at a time.

Multi-threading is a process that is used to improve CPU performance. This way, more than one person can manage the program at the same time, or the same person can handle several requests at the same time. Multi-threading is achieved by executing several processes that the operating system supports.

For example, a web browser can have multiple threads running at the same time. For example, while you’re scrolling through a page, you can download an app or document, listen to music, print something, and more.

What are the most popular methods of session management in servlet?

There are three main methods of session management in servlet:

URL rewriting adds a unique session ID to each URL as a way to manage sessions. When the browser requests a new page, the session ID is sent back to the server. It allows the server to associate the request with a specific session.

HttpSession: It is a built-in interface in Servlet used to store session data on the server side.

Cookies: Cookies are data sent by a servlet to a clients browser. The browser saves cookies and sends them back to the server in subsequent requests.

Explain the difference between synchronous and asynchronous programming.

In synchronous programming, the program execution happens in a sequential and blocking manner. In other words, each line of code is run one after the other, and the program has to wait for the current task to finish before moving on to the next one.

Asynchronous programming, on the other hand, is a way of writing code where the execution of the program happens in parallel and without blocking. In this model, more than one task can run at the same time, and the progress of one task does not depend on the progress of another.

What is the difference between Fail-Fast and Fail-Safe iterators?

What are the advantages of pair programming?

Pair programming helps teams to collaborate and share knowledge among the members. As two developers work together to complete the task, it ensures better code quality. It also helps in detecting bugs easily and identifying the scopes for improvement. Besides that, pair programming promotes better communication between team members and builds a positive work environment.

What is the event loop in JavaScript?

The event loop is a fundamental part of the JavaScript runtime environment. An event loop in JavaScript is a mechanism that executes tasks in a non-blocking manner. It continuously checks the message queue for new events to process and runs the corresponding event handlers.

It controls how tasks and events are carried out, which lets the runtime handle asynchronous tasks like network requests and file I/O without stopping other tasks.

Example:

How will you prevent a bot from scraping a public API?

Its impossible to completely prevent data scraping if the data within the API is publicly accessible. However, throttling is an effective way to deter bots from scraping a public API. It can prevent a device from making a certain number of requests within a specific time.

Moreover, an HTTP error should be thrown on exceeding a defined number of requests. A good bot detection solution can also tell what kind of visitors you have and automatically block any malicious bots that scrape your website.

Talk about connection leaks in Java and how they can be fixed.

In Java, a connection leak happens when a database connection is not properly closed after it has been used. This means that other parts of the application or other applications can’t use the connection again. This can slowly use up all available connections, and eventually the app will stop working because it doesn’t have enough resources.

To fix a Java connection leak, you must always explicitly close database connections when they are no longer needed. This should be done in the last block, but it’s not necessary if an exception happens.

How do you create a callback in JavaScript?

JavaScript callback functions can be used synchronously and asynchronously. An important reason for callback functions is that many actions don’t stop a program or function from running until they’re done.

In JavaScript, we need to pass a callback function as a parameter to another function and then call it back when the job is done.

Example:

What steps will you take to reduce a web applications load time?

The following are the most common ways to reduce the load time of web applications:

• Compress and optimize the s on your web application.
• Keep your CSS and JavaScript code in separate files that are not part of the HTML markup.
• Reduce the file size of JavaScript and style sheets.
• Cut down on how many HTTP requests a web page has to make.
• Place script references at the bottom of your HTML page.
• Reduce the number of 301 redirects.
• Allow browser caching so that the page doesn’t have to be reloaded every time a user visits it.

What is the Zip() function in Python?

Zip() is an inbuilt function in Python that takes iterable (such as lists, arrays, etc. ) as input and returns a single iterator of tuples. Each tuple contains the n-th elements from each of the input iterables. The zip function combines elements from each of the iterables.

For example, if you have two lists [1, 2, 3,. ] and [A, B, C,. ], the zip function will combine them into a single list [(1, A), (2, B), (3, C),. ].

What is a deadlock in Java, and how to avoid it?

Deadlock is a situation in Java when two or more threads are trying to access the same object. It happens only in the case of multi-threading. We can avoid a deadlock situation by using the following ways.

Avoid nested locks: Avoid giving a lock to multiple threads if we have already given it to one.

Use lock timeouts: We can tell a thread how long to wait for a lock before it stops waiting.

Avoid Unnecessary Locks: Using locks unnecessarily can lead to a deadlock, and we should avoid it.

Use lock escalation: Lock escalation helps convert multiple locks into fewer ones, reducing the risk of deadlocks.

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