Node.js is a crucial part of the tech stack of many big companies, such as PayPal, Trello, Walmart, and NASA.
According to ZipRecruiter, a Node.js engineer in the US earns an average of $116,495 a year or approximately $56.01 an hour.
Interview prep is important if you are already a skilled Node JS engineer looking for a new role.
The following are some of the most common Node.js questions you will likely encounter in your next interview.
Node.js is a lightweight but powerful framework used for creating server-side web applications. This cross-platform JavaScript runtime environment is built on Google’s V8 JavaScript engine. Its design is similar to that of Ruby’s Event Machine and Python’s Twisted.
Node.js runs JavaScript code as a single thread. It thus means that it executes this JavaScript code at a time. However, through the libuv library, Node.js runs various threads that handle various tasks, such as reading files from a disk and network requests.
Concurrency is a situation whereby an application handles multiple tasks simultaneously. Node.js uses event loops where asynchronous code is pushed to the end of the event queue. Even though JavaScript is single-threaded, the event loop allows Node.js to perform non-blocking I/O operations by offloading I/O tasks to the system kernel.
It is the world’s largest software registry, with over 800,000 code packages. Node Package Manager is automatically installed when you install Node.js.
Despite JavaScript being single-threaded, an event loop allows Node.js to perform non-blocking I/O operations. Whenever possible, Node.js offloads operations to the system kernel.
These are objects in Node.js that trigger an event after sending a message that a certain action has been completed. JavaScript devs can thus write code that listens to events from an emitter.
WebAssembly System Interface (WASI) API implements the WebAssembly System Interface. WASI uses POSIX-like functions to give sandboxed web applications access to the underlying operating system.
Read-Eval-Print-Loop (REPL), in Node.js, is an interactive shell that processes Node.js expressions. The easy-to-use command line captures code inputs from a user, interprets, prints out the results, and loops it until the user signals an exit.
It is how we control the logic and flow of code in our applications. If statements can control the flow of the code to a specific direction based on the state of variables and outputs from functions.
Also known as the pyramid of doom, callback hell is a situation whereby multiple callbacks are nested within a function. Callback hell is associated with asynchronous programming and makes the code hard to understand and maintain.
Middleware is a function that has all access for responding to an object, requesting an object, and moving to the next middleware in the app’s request-response cycle. Middleware acts as a connection between the applications, data, and users.
Streams are a collection of data comparable with arrays and strings. However, these streams don’t have to fit in memory and might be available simultaneously.
Piping is the process of connecting multiple streams. For instance, you can pipe the read and write streams to enable the transfer of data from one file to another.
Buffer modules offer a way to handle binary data streams in a Node.js setting. In Node.js, Buffer is a global object; you don’t have to import using the ‘require’ keyword.
You can create an empty Buffer of the length of 15 using this syntax;
var buf = Buffer.alloc(15);Before we learn what event-driven programming is, we must understand these concepts;
Event-driven programming is a concept where code is written to respond to events. For instance, we can have an automated system where sensors detect when a certain temperature is reached.
Such systems will have event handlers that respond to events and ensure the appropriate action is taken.
The test pyramid shows the proportion of unit tests, integration tests, and end-to-end tests needed to develop an application fully. The test pyramid aids in developing a robust testing suite and determines the frequency and order of assessments.
Error-first callback pass errors and data. An error object is the first thing you pass to such functions and the second thing is the associated data. Error-first callback allows you to pass an error object, check if anything is wrong and then handle it. If no issue is detected, you go ahead with subsequent arguments.
Long-term support (LTS) is a software release that gets extended support from the developers. The extended support can be 2-5 years, unlike regular programs, which only get 6 months to 1-year support.
A URL module will split up (parse) a web address into readable parts. You need to include the require() method to use the URL module.
Libuv is a cross-platform library written in C programming language, and it provides an asynchronous, event-driven programming style. Libuv provides an event loop and callback-based notifications of I/O.
Test stubs are spies/ functions with pre-programmed behavior. Stubs can wrap up existing functions or can be anonymous.
You can use stubs when;
Package.json is the heart of a Node.js project. This file records important metadata about a project which is needed before publishing to NPM. Package.json defines a project’s functional attributes that NPM uses to run scripts, install dependencies and identify the entry point to the package.
JSON is the short form for JavaScript Object Notation. It is a lightweight format for transporting and storing data and is often used when data is sent from a web server to a web page.
A package.json file is written in JSON format.
Express.js is a Node.js framework with robust features for creating mobile and web applications.
You can install this minimalistic web framework using this command;
npm install express --save“require” command. For instance, “var http=require (“HTTP”)” will load the HTTP library.
These are functions that are called after a certain task is complete. Such a setting allows the program to run another piece of code and prevent blocking.
Modules are reusable JavaScript codes that help developers adhere to the DRY (Don’t Repeat Yourself) programming principle. Such modules also aid in breaking down complex logic into small, simple, and manageable chunks.
I/O is the short form for input/output. It refers to the interaction of the program with the system’s network and disk. Talking to databases, reading/writing data from/to a disk, and making HTTP requests are examples of I/O operations.
Exit codes are a specific group of codes that finish off processes.
Some of the most common Node.js exit codes are;
The reactor pattern in Node.js is used to avoid blocking I/O operations. A reactor pattern has a handler associated with Input/Output operations.
A reactor pattern follows this pattern;
When a message is sent through the asynchronous architecture. The server stores the information, and it will be notified when the task is completed.
Non-blocking APIs respond immediately with whatever data is available. However, it does not block executions but keeps running as per the requests.
V8 JavaScript was developed for Chromium and Google Chrome web browsers to improve JavaScript execution on web browsers. Instead of using an interpreter, the V8 translates JS code to more efficient code to achieve faster JavaScript execution speeds.
In a synchronous function, code executes in a particular sequence based on the instructions given by the program.
In an asynchronous function, code can execute in parallel. The next operation can occur in such a setting even if another process is being processed.
Various package installers come with configurations to manage packages in Node.js projects. Most of these packages use npm or yarn. Luckily, both provide access to almost all JavaScript libraries with extended functionalities.
This is a piece of code that runs between various asynchronous function calls.
We have covered most of the questions you will likely encounter in a Node.js interview. However, you must also ensure that you possess Node.js technical skills. Good luck as you prepare for the next interview.
You may also explore some NodeJS frameworks to speed up web and API development.
