Node.js is quite similar to Ruby’s EventMachine and Python’s Twisted but a step ahead of them. It has an event-driven architecture that has the capability of asynchronous I/O operations, which makes it capable of handling multiple concurrent requests.
One of the main positives of Node.js which makes it more popular is that it runs on various platforms such as Windows, Linux, macOS, Unix, and many more.
If you’re willing to become a node.js developer, there are few points which you should have to understand before getting started:
- Knowledge of web frameworks and their proper usage is not enough, an in-depth knowledge of core Node.js and its API is a must.
- Although Node.js is a server-side environment, and most of the work is done in the back-end, you must have knowledge of the front-end as it will be required for enhancing the user experience.
- A good understanding and hands-on experience with databases to store dynamic data will be needed to run the application with Node.js.
- You must be thorough with Node.js package management
- Being comfortable with a cloud platform is a plus point as you would not be serving your web applications through your PCs.
Top Node.js Interview Questions
Question: What can you tell me about Node.js?
It is one of the, most famous frameworks for developing web apps as it consists of an event-driven architecture that has the capability of asynchronous I/O. Node.js functions, unlike other frameworks, are non-blocking and follow event-driven architecture which makes it highly efficient to handle concurrent client requests, by using callbacks and hence is more preferable in situations where something faster and more scalable is required.
Node.js is generally coupled with a database and combined with a browser and JSON to develop fully functioning network applications. Node.js adapts the vital server-side development patterns such as MVVM, MVP, MVC, and repairs the interface between client-side (front-end) and server-side(back-end).
Question: Highlight some of the key features of Node.js?
- Asynchronous event-driven IO: Node.js follows an event-driven mechanism that does asynchronous I/O operations. This simply means that on receiving a request, Node.js executes that request parallelly with other requests, without interrupting their operations.
- Fast: Node.js is comparatively faster than other scripting languages. It works on the v8 engine, the one used by google chrome itself. Node.js is single-threaded which means it does not block any other operations. Thus all the operations get executed in no time.
- Highly Scalable: Node.js works on single-threaded loop events which allows it to support thousands of other existing operations, which makes it a highly scalable language.
- Active Community: Node.js has a highly active community that goes by the name “community committee” or “comm comm” which keeps Node. js constantly updated.
The Node.js community is divided into the following categories:
Question: Is Node.js completely based on a single thread?
Node.js performs non-blocking operations that enable it to delegate all callbacks to different threads for their execution. The Node.js run-time is responsible for handling this process.
So, even on getting multiple requests from the client-side, Node.js is capable of utilizing fewer resources of memory because of its event-driven paradigm.
Question: What does event-driven programming mean?
Answer: Event-driven programming is a type of programming pattern or paradigm in which the flow of the program is controlled by some specific events such as messages from other programs, sensor outputs, mouse clicks, etc. Event-driven programs have a main loop for event listening which then triggers the callback function after the detection of the event. Embedded systems can also achieve the equivalent with the help of interruptions in hardware instead of running the main loop constantly.
Any programming language can be used to write an event-driven program, but if a language with high-level abstractions is chosen, then it can make the task much easier and simpler.
Today, a lot of already existing GUI development tools and architectures depend on event-driven programming.
Question: Define “I/O” operations?
Answer: Input/Output (I/0) is defined as a program, operation, or device that can convey and receive information from one device or medium to another. There is a requirement of an I/O interface in case a processor is diving an I/O operation. I/O devices are the components of hardware employed by a person (or another system) to speak with a computer.
For example, the keyboard, mouse, mic, scanner all are input devices that input data, whereas monitors, projectors, speakers, printers are examples of output devices. The communication devices like modems and network cards are used for both I/O operations.
A computer system reads and writes the data to memory locations according to the given protocols. There is another way to do so through the instruction-based I/O which needs a CPU that has specialized instructions for I/O. There is a huge difference between an input and an output device determined by their processing rate of data and instructions.
Question: How Node.js works?
Whenever Node.js receives an invitation, it first completes its processing before moving on to subsequent requests. The loop is responsible for the conversion of all the external events into a mere callback function. This event loop calls all the event handlers at the correct time.
Hence, multiple functions get executed at a single time on the server-side during the processing of one request. This results in no delay and the other functions do not have to wait for their turn to get processed.
Question: Name the various API functions supported by Node.js?
Answer: API stands for Application Programming Interface. Node.js supports the following types of API functions:
- Asynchronous, Non-blocking functions
- Synchronous, Blocking functions
Asynchronous Functions, Non-blocking functions: These functions as the name suggests, operate asynchronously. This simply states that when a request is made by Node.js, it doesn’t get blocked until it is received. Instead, it will be sent to a subsequent API, and the server will be responded to by a notification mechanism. To place it in layman’s terms, these functions allow working further while the request is being handled. Example: Emails, online forums, etc.
Synchronous, Blocking functions: These functions on the other hand, unlike synchronous functions, act as blocking functions. This simply means that these functions will make the calling system await a response. Thus, when a system uses synchronous APIs, it expects to urge immediate data when requests are made. These sorts of APIs are used where there are ample connectivity and availability with latency being low. To place it in layman’s terms, the appliance will request and await a response until the worth is returned. Example: Instant messaging, video meetings.
Question: What do you understand by the control flow functions?
Answer: Control flow in programming is a way in which a method or statement is computed. There is a linear flow in the majority of the programming languages, which means that statements get executed at a time. These functions are chunks of code, which when the request is made by the user, gets executed. Control Flow functions help in the execution of the functions according to the order in which the call is made i.e, they follow the first come first serve(FIFO) order.
Node.js is asynchronous single-threaded, so it does not let the other functions await while it executes some function. Instead, it registers the callback and returns it back to the node so that there is no delay and other functions get executed simultaneously.
Question: Explain NPM.
The registry doesn’t have any vetting process for submission, which suggests that packages found there are often inferior, insecure, or malicious, user reports play a crucial role in taking down packages that violate policies. Stats including the number of downloads are exposed by npm, which helps the developers to get the idea to judge the packages and their standard.
Packages that are locally dependent on certain projects can also be managed by npm. In a local project, if npm is used as the package manager, it provides the facility to install all dependencies of the project using a single command.
Question: What are the two arguments that async.queue takes as input?
Answer: Async::Queue is an async function that is used for processing a queued task with the required concurrency. The tasks that are passed as arguments to the async.queue are processed simultaneously with its worker routine up to the given concurrency level.
Asyn::Queue takes two arguments as input:
- Task function: It’s a set of functions that are needed to run. It is often an array, an object, or any iterable structure. The task function also takes up two parameters as input:
- the task that needs to be performed
- the callback function.
These tasks will be processed in FIFO order, i.e. when a task is finished, the callback function is called with the results.
- Concurrency value: It is the number of queued functions (concurrency level) that run in parallel. The tasks passed to the async.queue is processed simultaneously with its worker routine up to the required concurrency level.
Question: State the difference between Node.js vs Ajax?
Question: Describe the advantages and disadvantages of Node.js?
Answer: The advantages and disadvantages of Node.js are as follows:
|Asynchronous event-driven paradigm in operations handles multiple concurrent requests.||It does not provide complete scalability. CPU-heavy applications can get complex to work with.|
|It provides the ability to use the same piece of code between both the browser and the server.||Node.js demands a lot of changes in the code due to the instability of API|
|It supports an active and vibrant community, with lots of code shared regularly via Github, etc.||Despite the high demand for Node.js, there are only a few experienced Node.js developers present currently.|
Question: What are the types of streams present in Node.js?
Answer: Streams in Node.js is a way to handle end-to-end information exchange such as network communication, reading, and writing files. They are memory efficient as we don’t have to load a huge amount of data in the memory, which interns save time as well. Mainly, Node.js has four types of Streams:
- Writable: This stream supports the write operation. Example: fs.createWriteStream()
- Readable: This stream supports the read operation. Example: fs.createReadStream()
- Duplex: This stream supports both read and write operations. For example, net.Socket
- Transform: This stream enables the modification of a duplex stream.
Question: Name some of the popularly used libraries in Node.js?
Answer: Node.js provides a lot of libraries which makes it flexible for the developers to work with it. However, some of these libraries are highly popular and are used widely by the developers:
- Express: Express is the most popular Node web framework due to its minimalism and flexibility. It is the fundamental library for a lot of web frameworks in Node.
- Gulp: Gulp is a command-line toolkit for Node. js that helps automate processes and enhance workflow by running repetitive tasks with ease.
- Async: This utility module enables us to directly install Node JS through npm. This installation is done directly into the browser.
- Loadash: Loadash is a handy reference library that provides helper functions for common programming tasks such as Array, Function, Object, and Collection.
- Cheerio: Cheerio is an open-source library that helps developers interpret and analyze web pages by parsing the HTML and XML pages using a jQuery-like syntax.
- Nodemailer: Nodemailer is a module for Node. js applications and is used for sending emails from Node JS.
Question: What is libuv?
Answer: Libuv is a widely used multi-platform library present in Node.js. It is used to enhance the asynchronous I/O functionality of Node.js. It was created for Node.js primarily but now has been used alongside other systems such as Luvit, Pyuv, and more.
Important features of libuv library:
- File system event handling
- Child forking and handling
- Asynchronous UDP and TCP sockets
- Asynchronous file handling and operations
- High-resolution clock
Question: Mention the types of modules offered by Node.js.
Answer: Node.Js offers majorly three 3 types of modules;-
- Third-party modules: These modules are external, provided with advanced functionalities. They can be created by simply downloading them via NPM.
- Core Modules: Core modules consist of basic functionalities only to keep the Node.js lightweight. These modules load automatically when the Node.js process initiates. Example: URL, HTTP, path, etc.
- Local Modules: As the name suggests, these modules are created by the user itself. These modules have much more functionalities than core modules and can be downloaded via NPM.
Question: What do you know about callback hell?
- Callback hell is a severe issue that is caused due to multiple nested callbacks. Due to this, callback hell is also referred to as the pyramid of doom.
- Previous callbacks result in the arguments of each and every callback. So, the structure of the code resembles a pyramid which also affects its readability and maintainability.
- An error in any one of the functions results in affecting all other functions too.
Question: What is package.json?
- In order to use this file, it must be present in the outermost or main folder of every Node.js Package or Module.
- The file is named “package” because it contains multiple directive elements which govern the handling of other modules.
- Package.json is used by Node Package Manager (NPM). It consists of all details of the Node.js project.
Question: Does Node.js support multi-core platforms?
Answer: Yes, Node.js can support multi-core systems, but since it is a single-threaded platform; you need to fork multiple processes in order to facilitate multicore CPUs in it. This process is known as “clustering”, supported by the Node.js Cluster module.
The cluster module provides a way of starting multiple Node.js worker processes that will run simultaneously and share the same port and helps you to spawn new child processes on the operating system using the child_process.fork() method. Each process communicates independently with the main process by IPC, so a shared state between the child processes can not be used.
Question: Explain the role of the request process in Node.js.
Answer: In Node.js, the request module is used to make the HTTP class and handle the requests from the server. The request module by default follows redirects to handle the HTTP calls.
So, An HTTP request is basically a message that is a request made by the client over the web. HTTP is the fundamental format used to structure such requests for effective communication between the client and the server.
The request module is used to fulfill several requests from the server and if there is a large file that takes a long time for the server to perform, a request can be made to ensure that other requests don’t get affected by that file and remain uninterrupted.
Question: What is the chaining process in Node.js?
Answer: In Node.js, chaining can be performed using the async npm module. The async module provides the following most popular methods for chaining functions:
- parallel(tasks, callback): In the parallel chaining process, all the functions get executed parallelly in practice through I/O switching. The callback function is triggered if any of the functions throws an error.
- series(tasks, callback): As the name suggests, functions are executed in series i.e, a function is being executed only after the completion of the previous one. Functions will not get executed if any of the previous functions gives an error.
Question: What is a child_process module in Node.js?
Answer: The child_process module in Node.js helps to access the OS functionalities, it runs any system command inside a child process. This module is used to spin a child process in order to establish communication between the processes within a messaging system.
As Node.js follows an event-driven model, it also supports the creation of child processes in parallel with the event-driven architecture.
In Node.js, there are 4 different methods to create a child process:
- spawn(): This method is used to generate a new process using the command line arguments.
- fork(): This method is used to create a separation of tasks from the main event loop that needs evaluation.
- exec(): This method is used to create a child process by first creating a shell and then executing a command.
- execFile(): This method is used to create the specified executable file folder as a new process instead of generating a shell by default.
Question: Explain the concept of middleware in Node.js?
Answer: A middleware function is a function that has access to all the requests made by the user. This simply means that in an application’s request cycle, these functions have a command to all the response objects and the next subsequent function present in the memory stack. This function of middleware is represented by a keyword, usually named next. Below are some of the most important tasks, performed by middleware in Node.js:
- Execution of all types of code
- Modification of all the request objects
- Completion of the request-response cycle
- Call the next middleware in the stack
Question: Differentiate between spawn and fork methods in Node.js?
Answer: The spawn() function generates a new process using the command line arguments. This function develops a module on the processor and then gets called by Node.js when the child processes return data.
The fork() method on the other side is an object of the already existing process created by the spawn() method. Spawning makes sure that the tasks get handled at any given point, so it keeps more than one worker node active all the time.
Question: What are stubs in Node.js?
Answer: In Node.js, stubs are functions that assess and analyze the behavior of individual components. Stubs provide the details of the executed functions while running the test cases. Following are some of the properties of the stubs:
- They can also be anonymous.
- They can also be wrapped in already existing functions.
- They also affect the behavior of components or modules.
- They are dummy objects that are used for testing.
Question: Why do module exports exist in Node.Js?
Answer: Module exports are the set of instructions, responsible for commanding Node.js which chunks of the program (arrays, class, etc) to “export” from the existing file to provide its access to the other files. Modules in Node.Js are responsible for the integration of all the pieces of code into a single code. This process is done by transferring all the related functions into one common file.
If you’re using Node.js to create your application, making use of the modules is very vital in order to create applications and software systems.
Question: What is the use of the connect module in Node.js?
Answer: Connect module is a simple framework that is used to combine middleware handle requests together. It provides a safe passage between HTTP and Node.js to communicate. This module provides a utility function that helps in registering it with HTTP so that the user does not have to invoke the HTTP.createServer(app)
Connect also provides a method called createServer, which returns an instance. This instance inherits an extended version of HTTP.Server. The extensions of Connect module usually make it flexible to plug in the middleware. That is one of the main reasons why the Connect module gets symbolized as a “middleware framework,” and is often analogized to Ruby’s Rack.
Question: What is meant by tracing in Node.js?
Answer: Tracing is a method in Node.js that is used to trace and identify the node application method to execute it. Tracing makes monitoring of the application of data quite easy whether it’s on the function or system level. It also checks the validation of these functions by ditching them into a log file.
Question: How can you scale the Node.Js application?
Answer: The scaling of an application determines the potential of an application to get efficient in time and increase the ability to handle requests.
In Node.js, scaling takes place in mainly three steps:
- Cloning: To scale a big application, the easiest way would be to clone it multiple times so that each cloned instance can handle some part of the workload (for example, a load balancer).
- Decomposing: An application can also be scaled by decomposing it on the basis of functionalities. This way, we will have multiple applications with their corresponding code bases. Some of these can also have their own dedicated interfaces and databases.
- Splitting: Another way to scale an application would be to split it into multiple instances, where each instance will be having the responsibility of a part of the data. Hence, this technique goes by the name horizontal partitioning, in databases.
Question: Differentiate between readFile and createReadStream in Node.js?
Answer: Following are some of the major differences between readFile and createReadStream:
|readFile loads the whole file at a time into the memory.||createReadStream reads the entire file in chunks of specified sizes.|
|Data is received relatively slower as first the whole file is read.||Data is received faster as it is passed in bits.|
|Memory clean-up is easy in Node.js.||Memory clean-up is not an easy task.|
|Requests cannot be scaled at a given time.||File content is piped directly to the HTTP response object.|
Question: What do you understand by global objects in Node.js?
Answer: Global objects in Node.js are globally accessible and they are accessible in every module. Global objects don’t need to be added to the application, they can be accessed directly. Such objects can be functions, modules, objects, and strings. Such objects are not necessarily in the global scope, they can also be in the module scope.
Question: What is a passport in Node.js?
Answer: Passport is an extremely flexible and popular middleware in Node.js, used for authentication. It can be easily integrated with applications based on express.js. Unique authentication mechanisms are required for every application, so single modules are provided using passport.
This makes it an easy task to assign strategies to the applications, and it also avoids any kind of dependencies. Such strategies are an extensible set of plugins that the passport uses to authenticate requests. Passport delegates all other functionalities to the application so that encapsulation in the modules remains intact. Passport as a tech stack is currently used widely by a lot of companies including Swvl.
Question: Explain the usage of a buffer class in Node.js.
Answer: The buffer class in Node.js provides a way to deal with TCP streams (file system) and handle the octet streams.
- This class provides instances to store and manipulate streams of raw binary data, this is similar to storing an array of integers, but the difference is that there is a raw memory allocation outside the V8 heap.
- Buffer class in Node.js is a global object so it can be accessed directly in the application without actually importing any modules.
- Node.js provides some ways to create and manipulate your own buffer.
- After creating a buffer, there are multiple interactions that can be done with the buffer.
Question: Explain REPL at Node.Js.
Answer: REPL (Read Eval Print Loop) is an interactive shell used to process Node’s expressions. It is a computer environment such as a UNIX/LINUX shell that interacts by evaluating output when a command is entered on the shell.
Below are some of the tasks performed by REPL:
- Print −This is the task of printing the result.
- Loop −This task loops the above command until ctrl+c is pressed twice.
Question: What is the major drawback of Node.js?
Answer: One of the most challenging difficulties that the developers face with Node.js is to process a single thread to measure multiple core servers.
Question: How does the DNS lookup function work in Node.js?
Answer: The DNS lookup function/ method in Node.js is an inbuilt API of the DNS module that uses a web address as its parameter and resolves IP addresses of the required hostname for given parameters into the primary found A (IPv4) or AAAA (IPv6) record accordingly. This method has three parameters namely hostname, options, and callback.
The return value of this method is an error, IP addresses, and family of IP addresses through a callback function depending upon the values passed to the method as parameters.
Question: Mention the sections of event-driven programming?
Answer: The two sections of event-driven programming are:
- Event selection: Event selection occurs on click events. It responds when we make a click or use a shortcut key to execute a selection in a pull-down menu.
- Event handling: Event handling is a callback routine that controls the events and operates asynchronously when an event occurs. Event-driven programming is based on events and event handling.
Question: What do you understand about a test pyramid?
Answer: A test pyramid is a tool used to help developers by giving an idea of the required number of test cases executed in three stages, unit testing, integration testing, and combined testing. This indicates how testing is done using multiple layers. Test pyramid reduces the time required for the developers to analyze the impact or behavior of any change made into the code, by maintaining an ample number of test cases to develop an end-to-end project. The test pyramid is a fundamental and crucial topic that helps developers and QA testers to deal with the entire stack of the end product.
Question: Explain debugging in Node.js.
Answer: Node.Js has an in-built debugging application called a debugger. Debugging takes place when we start the Node.js with the debug statement along with the path of the script that needs to be debugged.
After that, a breakpoint will be generated into the source code, once the statement debugger is inserted in it. This is the process of debugging in Node.js.
Question: Explain CLI in Node.js.
Answer: Command Line Interface or CLI is a program, built-in on the computer where users type commands to perform the desired action. Command-line is highly useful in situations when you can’t simply make a click on the system.
Different operating systems have different command lines. Below are some of the command lines:
- Bash on Linux.
- The terminal of Mac.
- Command Prompt or Powershell on Windows
- Shell/ Command line/terminal on Unix and Ubuntu
1. NodeJS :
Question: What are the common challenges with Node.js?
- It does not provide complete scalability. CPU-heavy applications can get complex to work with.
- Relational databases with Node.js can be more complex.
- Node.js demands a lot of changes in the code due to the instability of API
- Despite the high demand for Node.js, there are only a few experienced Node.js developers present currently.
Question: Mention the framework most commonly used in node.js?
Answer: Currently, Express is the widely used and most popular framework that is used in Node.js. Apart from that, some other well-known Node.js frameworks are:
Question: What does it mean “non-blocking” in Node.js?
Question: What is the purpose of require() method in Node.js?
Question: How are child threads handled in Node.js?
Answer: Since Node.js is single-threaded, it does not exhibit the methods to manage threads. However, the use of the child threads can still be made using the spawn() method. To embed threading in an application in Node.js, the ChildProcess module has to be included explicitly in it. Handling of the child threads is done by spawning some asynchronous I/O tasks executing in the background. Using such libraries which are not single-threaded, multiple threads can be handled efficiently in Node.js.
Question: Why does Google use the V8 engine for Node.js?
This enhances an application’s performance while it’s executing and provides a facility for the users to get an experience with the real-time application. The V8 engines are widely used due to their excellent balance of performance and efficiency.
Question: What is the use of EventEmitter in Node.js?
Answer: The instances of the EventEmitter class emit an error event whenever the instances face any error. In such a situation, all of the specific functions of that particular event are synchronously called, this is known as calling the synchronous attachments. The objects of this class have a function that allows an attachment between the instances and the events.
This class is present in the events module and enables the handling of custom events along with their creation.
Question: Do you have any previous experience of working in a similar environment?
Answer: Interviewers ask such questions to assess your previous work or internship experience where you addressed similar working environments and similar technologies were involved. Answers to such questions should be honest and concise. Provide details wherever necessary, and discuss your relevant work experience.
Question: Can you provide any certification to give a boost to your application for this Node.js role?
Answer: Possessing a certificate of the tech stack and skills that are required in the job description is always beneficial. This creates a positive impression on the interviewer that you are familiar with the required technology and have an in-depth understanding of the concepts as well as the practical applications. This also boosts up your resume and helps it to stand out, adding immense value to it as well as to your knowledge.
In this guide, we discussed the top 50 interview questions on Node.js that are most frequently asked. We covered all the aspects of Node.js starting from the introduction of Node.js and moving forward to advanced topics such as Modules of Node.js, control flow and callback hell in Node.js, spawn() and fork() methods, the difference between Node.js and ajax, and why is Node.js has an upper hand on its counterparts. We skimmed through some important questions on these tools including their use, benefits, architectures, etc.
We certainly hope that this guide helps you to revise all the concepts of Node.js and its applications before you start hunting for Job Interviews and ace them with flying colors.