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Node Js · Question Set
File System & Streams interview questions for placements and exams.
Questions
14
Included in this set
Subject
Node Js
Explore more sets
Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for Node Js.
The Buffer class is used to handle binary data directly, especially in file streams or TCP connections. Buffers are similar to arrays of integers but represent raw memory. This allows efficient reading and writing of binary data.
const buf = Buffer.from('Hello');
console.log(buf.toString());For complete preparation, combine this set with full subject-wise practice for Node Js. You can also explore other subjects and sets from the links below.
Common file system flags include: 'r' for read, 'w' for write, 'a' for append, 'r+' for read/write, and 'wx' for write only if the file doesn’t already exist.
Callback hell occurs when multiple asynchronous functions are nested within each other, creating deep and unreadable code. It can be solved by using Promises or async/await for cleaner control flow.
// Callback Hell Example
fs.readFile('a.txt', () => {
fs.readFile('b.txt', () => {
fs.readFile('c.txt', () => {
console.log('done');
});
});
});A control flow function manages the order in which asynchronous functions are executed. It ensures that dependent functions wait for the previous ones to finish before running, avoiding messy callback chains.
Both create new processes. `spawn()` launches a new process with a given command. `fork()` is a special case of `spawn()` that creates a new Node.js instance for parallel execution, ideal for running multiple workers.
const { fork, spawn } = require('child_process');
const child = fork('worker.js'); // new Node process
const run = spawn('ls', ['-lh']); // system commandPiping connects the output of one stream directly into another stream, commonly used to transfer data efficiently between files or network responses. It eliminates manual data handling.
const fs = require('fs');
fs.createReadStream('input.txt').pipe(fs.createWriteStream('output.txt'));Use the `fs.open()` method to open a file. It takes a filename, flag (like 'r' for read or 'w' for write), and a callback. Always handle errors to avoid crashes.
const fs = require('fs');
fs.open('example.txt', 'r', (err, fd) => {
if (err) throw err;
console.log('File opened successfully');
});The Reactor Pattern is the design model behind Node.js’s non-blocking I/O system. It uses an event demultiplexer that listens for events and dispatches them to handlers asynchronously, improving performance and scalability.
The Test Pyramid represents the ideal balance of test types: more unit tests at the bottom, fewer integration tests in the middle, and even fewer end-to-end tests at the top. It ensures faster, stable, and maintainable testing strategies.
Node.js uses Google’s V8 engine because it compiles JavaScript directly into machine code for high performance. It supports just-in-time (JIT) compilation, making Node.js fast and efficient for both server and network operations.
Middleware functions in Node.js (especially in Express) process incoming requests before they reach route handlers. They can modify requests, add headers, handle authentication, or terminate the request-response cycle.
app.use((req,res,next)=>{
console.log('Request Time:', Date.now());
next();
});Common HTTP request methods include: GET (retrieve data), POST (create or modify), PUT (update), DELETE (remove), and PATCH (partial update). Node’s `http` and Express frameworks support them all.
Control flow manages async function calls by defining clear execution order. It executes one function, waits for its callback or promise, and then triggers the next one. Libraries like `async` simplify this with series or parallel task control.
REPL stands for Read-Eval-Print Loop. It is a Node.js command-line tool that allows developers to quickly test code snippets. You can type JavaScript directly into the terminal, and Node.js will execute and return results immediately — useful for debugging and experimenting.