Updated May 9, 2023
Introduction to Node.js Interview Questions and Answers
Node.js Interview Questions are a set of questions that are asked during an interview for a job related to Node.js technology. The questions examine a candidate’s proficiency and knowledge in Node.js development. It helps the interviewer analyze the person’s ability to develop scalable and secure Node.js applications.
The following article guides cracking the most common Node.js Interview Questions. Although each interview and job scope differs, these selected questions would help one break down the 2023 Node.js Interview Questions.
The article divides the questions into two categories:
Part 1 – Node.js Interview Questions (Basic)
Q1) What is Node.Js, and explain its features?
Answer:
Node.js is a runtime platform built on Google Chrome’s JavaScript engine. It uses a single-threaded model that employs the concurrency model for its events to loop. Rather than blocking an application, it enables the registration of a callback to a new application, allowing the current application to continue. This results in handling concurrent operations without creating multiple threads of execution. Node.js uses JavaScript with C or C++ to interact with a filesystem. Its main features are:
- Node.js library: Since all developers are already comfortable with JavaScript, Node.js has a library built over JavaScript, making it easy for developers to use.
- Single-Threaded and Highly Scalable: It uses a single thread for event looping. While responses may not reach the server on time, this does not block any operations. Regular servers have limited lines to handle requests, but Node.js creates a single thread to manage many requests.
- No Buffer: These applications do not need any buffer and send the data output in chunks.
- Concurrent Request Handling with Asynchronous Event-Driven I/O: All nodes of API in Node.js are asynchronous, enabling a node to receive a request for an operation. It can take new requests while working in the background. As a result, it handles all requests concurrently and does not wait for previous responses.
Q2) What is REPL in Node.js?
Answer:
REPL stands for Read-Eval-Print Loop. One can write programs that accept, evaluate, and print commands using these operations. It supports an environment similar to Linux or UNIX, where a developer can enter commands and receive a response with the output. The REPL performs the following functions:
- READ: It reads input from the user, parses it into JavaScript, and stores it in memory.
- EVAL: It executes the data structure that stores the information.
- PRINT: It prints the output received from executing the command.
- LOOP: It loops the above command until the developer presses Ctrl + C twice.
Q3) What is Callback Hell?
Answer:
Callback hell refers to nested callbacks that callback a procedure many times, rendering the code unreadable.
downloadPhoto('http://coolcats.com/cat.gif', displayPhoto)
function displayPhoto (error, photo) {
if (error) console.error('Download error!', error)
else console.log('Download finished', photo)
}
console.log('Download started')First, in Node.js, the ‘display photo’ function is declared. Then, the ‘downloadPhoto’ process is called, and it passes ‘displayPhoto’ as its callback.
Q4) What is Tracing?
Answer:
Tracing in Node.js allows you to collect information generated by V8. You can start Node.js with the ‘-trace-events-enabled’ flag to enable tracing. The specific categories of data to be recorded can be specified with the ‘–trace-event-categories’ flag. To view the logs generated by tracing, navigate to ‘chrome://tracing’ in the Chrome browser.
Q5) How to avoid Callback Hell?
Answer:
Node.js uses only a single thread, which can lead to queued events. Thus, whenever a long-running query finishes its execution, it runs the callback associated with the question. To address this issue, the following mechanisms can be followed:
- Modular code: Splitting code into smaller modules and joining them to the main module can achieve the desired result.
- Promise Mechanism: It is an alternate way to write async code, ensuring either a development or an error. They take two optional arguments, and depending on the promise’s state, one will be called.
- Use of Generators: These routines wait and resume using the “yield” keyword. They can suspend and resume asynchronous operations.
- Async Mechanism: The method provides a sequential flow of execution. It has <async.waterfall> API that can pass data from one process to another using the next callback. The caller is the primary method and is called only once through a callback.
Part 2 – Node.js Interview Questions (Advanced)
Q6) How to load HTML in Node.js?
Answer:
To load HTML in Node.js, we should change the ‘Content-type’ in the HTML code from plain text to HTML text. Here is an example where a static file is created on the server:
fs.readFile(filename, "binary", function(err, file) {
if(err) {
response.writeHead(500, {"Content-Type": "text/plain"});
response.write(err + "\n");
response.end();
return;
}
response.writeHead(200);
response.write(file, "binary");
response.end();
});
This code can be modified to load as HTML page instead of plain text.
fs.readFile(filename, "binary", function(err, file) {
if(err) {
response.writeHead(500, {"Content-Type": "text/html"});
response.write(err + "\n");
response.end();
return;
}
response.writeHead(200, {"Content-Type": "text/html"});
response.write(file);
response.end();
});Q7) Explain EventEmitter in Node.js?
Answer:
This is one of the most popular Node.js interview questions. The event module in Node.js can have an EventEmitter class, which is helpful in raising and handling custom events. One can access it with the below code:
// Import events module
var events = require('events');
// Create an eventEmitter object
var eventEmitter = new events.EventEmitter();When an error occurs, it also calls an error event. When a new listener is added, the ‘newListener’ event is triggered. Similarly, when a listener is removed, ‘removeListener’ is called.
Q8) What is NPM?
Answer:
NPM stands for Node Package Manager and has two main functions:
- It works on Online Repository for node.js packages, which is available at <nodejs.org>.
- It works as a command-line utility and does version management.
One can verify the version using the below command:
npm –versionTo install any module, one can use:
npm install <Module Name>Q9) Explain the use of method spawn() and fork()?
Answer:
The method works to launch a new process with a given set of commands. The command is as follows:
child_process.spawn(command[, args][, options])The fork method is a special case for the spawn() method. One can use it as follows:
child_process.fork(modulePath[, args][, options])Q10) Explain the control flow function and the steps to execute it?
Answer:
A control flow function is a code that runs between asynchronous function calls. To execute the code, follow these steps:
- Control the order of execution.
- Collect the data.
- Limit concurrency.
- Call the next step in the program.
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