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Node Js · Question Set
Event Loop 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 Event Loop is the core of Node.js’s asynchronous architecture. It continuously checks the event queue and executes callbacks or promises when their operations complete. It allows Node.js to handle thousands of requests on a single thread.
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.
First, import Express, create an app using `express()`, define routes, and start listening on a port. Express automatically handles HTTP requests and responses.
const express=require('express');
const app=express();
app.get('/',(req,res)=>res.send('Hello World'));
app.listen(3000);Streams are objects that let you read or write data continuously. There are four types: Readable, Writable, Duplex, and Transform. They make data handling efficient, especially for large files.
const fs=require('fs');
fs.createReadStream('input.txt').pipe(fs.createWriteStream('output.txt'));Use `npm install package-name` to add, `npm update package-name` to update, and `npm uninstall package-name` to remove a dependency.
npm install express npm update express npm uninstall express
package.json holds project metadata like name, version, dependencies, and scripts. It is created using `npm init` and allows npm to install and manage required packages for your project.
{ "name": "my-app", "dependencies": { "express": "^4.18.0" } }EventEmitter is a core module that allows objects to emit and listen for events. It forms the base for asynchronous communication in Node.js. You can register listeners with `.on()` and trigger them with `.emit()`.
const EventEmitter=require('events');
const emitter=new EventEmitter();
emitter.on('greet',()=>console.log('Hello!'));
emitter.emit('greet');Node.js provides asynchronous (non-blocking) and synchronous (blocking) APIs. Asynchronous APIs allow other code to execute while waiting for results, whereas synchronous APIs block the event loop until completion.
The URL module helps parse, resolve, and format URLs. It splits a web address into parts like hostname, path, and query parameters, making it easy to work with HTTP requests.
const url=require('url');
const q=url.parse('https://example.com/home?id=10',true);
console.log(q.host, q.query.id);Express.js is a minimal and flexible web framework built on Node.js. It simplifies handling routes, requests, and middleware to build RESTful APIs and web apps quickly.
Use the HTTP module, call `createServer()` with a callback that handles requests and responses, and listen on a port.
const http=require('http');
http.createServer((req,res)=>{
res.write('Hello World');
res.end();
}).listen(8080);All Node.js APIs are asynchronous, meaning they don’t block execution. The server can process other requests while waiting for one operation to finish. Results are handled using callbacks, promises, or async/await.
You can write async functions using `async` and `await`. The function waits for a Promise to resolve before executing the next line, making async code easy to read and debug.
async function getData(){
const res=await fetch('https://api.com');
const data=await res.json();
console.log(data);
}Event-driven programming means the flow of the program is determined by events such as user actions or messages from other programs. In Node.js, events trigger callback functions through the EventEmitter system, allowing non-blocking, asynchronous behavior.
process.nextTick() executes a callback immediately after the current operation, before the next event loop iteration. setImmediate() schedules the callback for the next iteration of the event loop, after I/O events. nextTick() runs sooner.
process.nextTick(()=>console.log('Next Tick'));
setImmediate(()=>console.log('Immediate'));