Node.js Interview Coding Problems & Solutions

Q1. Implement a custom EventEmiiter class from scratch

class EventEmitter {
  constructor() {
    this.events = {};
  }
  on(event, listener) {
    if (!this.events[event]) this.events[event] = [];
    this.events[event].push(listener);
  }
  emit(event, ...args) {
    if (this.events[event]) {
      this.events[event].forEach(listener => listener(...args));
    }
  }
  off(event, listenerToRemove) {
    if (!this.events[event]) return;
    this.events[event] = this.events[event].filter(listener => listener !== listenerToRemove);
  }
}
// Usage:
const emitter = new EventEmitter();
emitter.on('greet', name => console.log('Hello ' + name));
emitter.emit('greet', 'Node.js');

Builds a publish-subscribe event emitter mechanism managing listener callback arrays.

Q2. Read a large file line by line using ReadStreams and ReadLine

const fs = require('fs');
const readline = require('readline');

async function processLineByLine(filePath) {
  const fileStream = fs.createReadStream(filePath);
  const rl = readline.createInterface({
    input: fileStream,
    crlfDelay: Infinity
  });
  for await (const line of rl) {
    console.log('Line from file:', line);
  }
}
processLineByLine('./large-log.txt');

Streams massive log files line by line asynchronously without overflowing V8 heap memory.

Q3. Implement a custom Promise.all implementation

function promiseAll(promises) {
  return new Promise((resolve, reject) => {
    if (!Array.isArray(promises)) return reject(new TypeError('Arguments must be an array'));
    const results = [];
    let completed = 0;
    if (promises.length === 0) return resolve(results);

    promises.forEach((promise, index) => {
      Promise.resolve(promise)
        .then(value => {
          results[index] = value;
          completed++;
          if (completed === promises.length) resolve(results);
        })
        .catch(reject);
    });
  });
}

Resolves when all input promises fulfill, or rejects immediately if any promise rejects.

Q4. Implement rate limiter middleware in Express.js

const rateLimit = require('express-rate-limit');

const apiLimiter = rateLimit({
  windowMs: 15 * 60 * 1000,
  max: 100,
  message: 'Too many requests from this IP, please try again later',
  standardHeaders: true,
  legacyHeaders: false,
});

// Usage in Express app:
// app.use('/api/', apiLimiter);

Protects backend API endpoints against abuse by throttling client request frequencies.

Q5. Implement Cluster module load balancer setup

const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;

if (cluster.isPrimary) {
  console.log('Primary process ' + process.pid + ' is running');
  for (let i = 0; i < numCPUs; i++) cluster.fork();
  cluster.on('exit', (worker) => {
    console.log('Worker ' + worker.process.pid + ' died. Forking new one...');
    cluster.fork();
  });
} else {
  http.createServer((req, res) => {
    res.writeHead(200);
    res.end('Hello from worker ' + process.pid);
  }).listen(8000);
}

Spawns child worker processes sharing port bindings to utilize multi-core CPU architectures.

Q6. Implement JWT Authentication Middleware

const jwt = require('jsonwebtoken');

function authenticateToken(req, res, next) {
  const authHeader = req.headers['authorization'];
  const token = authHeader && authHeader.split(' ')[1];
  if (!token) return res.sendStatus(401);

  jwt.verify(token, process.env.ACCESS_TOKEN_SECRET, (err, user) => {
    if (err) return res.sendStatus(403);
    req.user = user;
    next();
  });
}

Verifies bearer tokens in request headers to protect private API routes.

Q7. Build a simple caching middleware using Map

const cache = new Map();

function cacheMiddleware(duration) {
  return (req, res, next) => {
    const key = req.originalUrl || req.url;
    const cachedResponse = cache.get(key);
    if (cachedResponse) {
      return res.send(cachedResponse);
    }
    res.sendResponse = res.send;
    res.send = (body) => {
      cache.set(key, body);
      setTimeout(() => cache.delete(key), duration * 1000);
      res.sendResponse(body);
    };
    next();
  };
}

Caches HTTP responses in memory for high-speed retrieval.

Q8. Implement graceful shutdown handling

const express = require('express');
const app = express();
const server = app.listen(3000);

process.on('SIGTERM', () => {
  console.log('SIGTERM signal received: closing HTTP server');
  server.close(() => {
    console.log('HTTP server closed');
    // Close database connections here
    process.exit(0);
  });
});

Ensures ongoing active requests complete successfully before shutting down server processes.

Q9. Implement a debounce helper function in Node

function debounce(fn, delay) {
  let timeoutId;
  return function (...args) {
    clearTimeout(timeoutId);
    timeoutId = setTimeout(() => {
      fn.apply(this, args);
    }, delay);
  };
}
// Usage: const debouncedLog = debounce(() => console.log('called'), 300);

Delays function executions until specified idle time intervals elapse.

Q10. Hash passwords securely using bcrypt

const bcrypt = require('bcrypt');

async function hashPassword(plainPassword) {
  const saltRounds = 10;
  const hash = await bcrypt.hash(plainPassword, saltRounds);
  return hash;
}

async function verifyPassword(plainPassword, hash) {
  return await bcrypt.compare(plainPassword, hash);
}

Salts and hashes passwords securely prior to database persistence.

Q11. Implement a custom Promise.race implementation

function promiseRace(promises) {
  return new Promise((resolve, reject) => {
    for (let p of promises) {
      Promise.resolve(p).then(resolve, reject);
    }
  });
}

Returns a promise that fulfills or rejects as soon as one of the input promises settles.

Q12. Implement deep clone function for JavaScript objects

function deepClone(obj, hash = new WeakMap()) {
  if (Object(obj) !== obj) return obj;
  if (hash.has(obj)) return hash.get(obj);
  let result = obj instanceof Date ? new Date(obj)
    : obj instanceof RegExp ? new RegExp(obj.source, obj.flags)
    : obj.constructor ? new obj.constructor() : Object.create(null);
  hash.set(obj, result);
  return Object.assign(result, ...Object.keys(obj).map(key => ({ [key]: deepClone(obj[key], hash) })));
}

Recursively clones complex nested objects handling circular references.

Q13. Implement basic connection pooling simulation

class ConnectionPool {
  constructor(maxSize) {
    this.maxSize = maxSize;
    this.pool = [];
    this.active = 0;
  }
  acquire() {
    if (this.pool.length > 0) return this.pool.pop();
    if (this.active < this.maxSize) {
      this.active++;
      return { id: Math.random() };
    }
    return null;
  }
  release(conn) {
    this.pool.push(conn);
  }
}

Manages finite database connection resource pools efficiently.

Q14. Implement custom Error handling middleware in Express

function errorHandler(err, req, res, next) {
  const statusCode = err.statusCode || 500;
  res.status(statusCode).json({
    success: false,
    error: {
      message: err.message,
      status: statusCode,
    }
  });
}

Captures unhandled errors across Express routes and formats standard JSON error responses.

Q15. Implement a file logger utility class

const fs = require('fs');
const path = require('path');

class Logger {
  constructor(filename) {
    this.filepath = path.join(__dirname, filename);
  }
  log(message) {
    const entry = `[${new Date().toISOString()}] ${message}\n`;
    fs.appendFile(this.filepath, entry, (err) => {
      if (err) console.error('Logging failed:', err);
    });
  }
}

Appends timestamped log records into physical files asynchronously.

Q16. Create a simple TCP Echo Server using net module

const net = require('net');

const server = net.createServer((socket) => {
  console.log('Client connected');
  socket.on('data', (data) => {
    socket.write('Echo: ' + data);
  });
  socket.on('end', () => console.log('Client disconnected'));
});
server.listen(8080, () => console.log('TCP server listening on port 8080'));

Listens for raw TCP socket data streams and echoes back data.

Q17. Build a simple UDP Server using dgram module

const dgram = require('dgram');
const server = dgram.createSocket('udp4');

server.on('message', (msg, rinfo) => {
  console.log(`Server got: ${msg} from ${rinfo.address}:${rinfo.port}`);
});
server.bind(41234);

Handles connectionless UDP datagram message packets.

Q18. Implement request body parser middleware from scratch

function bodyParser(req, res, next) {
  let body = '';
  req.on('data', chunk => {
    body += chunk.toString();
  });
  req.on('end', () => {
    try {
      req.body = JSON.parse(body);
    } catch (e) {
      req.body = {};
    }
    next();
  });
}

Collects incoming HTTP request chunk buffers and parses JSON payloads.

Q19. Implement a worker thread CPU-bound task runner

const { Worker, isMainThread, parentPort, workerData } = require('worker_threads');

if (isMainThread) {
  module.exports = function runWorker(data) {
    return new Promise((resolve, reject) => {
      const worker = new Worker(__filename, { workerData: data });
      worker.on('message', resolve);
      worker.on('error', reject);
    });
  };
} else {
  const result = workerData * 1000;
  parentPort.postMessage(result);
}

Offloads heavy calculations to parallel background worker threads.

Q20. Implement a retry mechanism for failed asynchronous tasks

async function retryOperation(fn, retries = 3, delay = 1000) {
  try {
    return await fn();
  } catch (error) {
    if (retries <= 0) throw error;
    await new Promise(res => setTimeout(res, delay));
    return retryOperation(fn, retries - 1, delay * 2);
  }
}

Repeats failing asynchronous tasks with exponential backoff delays.

Q21. Implement custom API request validation middleware

function validateSchema(schema) {
  return (req, res, next) => {
    const { error } = schema.validate(req.body);
    if (error) {
      return res.status(400).json({ error: error.details[0].message });
    }
    next();
  };
}

Validates incoming HTTP request body data against predefined schemas before routing.

Q22. Implement simple in-memory session store

class MemoryStore {
  constructor() {
    this.sessions = new Map();
  }
  set(sessionId, data, ttl = 3600) {
    const expiry = Date.now() + ttl * 1000;
    this.sessions.set(sessionId, { data, expiry });
  }
  get(sessionId) {
    const session = this.sessions.get(sessionId);
    if (!session) return null;
    if (Date.now() > session.expiry) {
      this.sessions.delete(sessionId);
      return null;
    }
    return session.data;
  }
}

Manages user session tokens and payloads in server RAM with expiration control.

Q23. Implement a custom JSON file database wrapper

const fs = require('fs');
class JsonDatabase {
  constructor(filepath) {
    this.filepath = filepath;
    if (!fs.existsSync(this.filepath)) fs.writeFileSync(this.filepath, JSON.stringify({}));
  }
  read() {
    return JSON.parse(fs.readFileSync(this.filepath, 'utf8'));
  }
  write(data) {
    fs.writeFileSync(this.filepath, JSON.stringify(data, null, 2));
  }
}

Provides simple synchronous read/write storage operations over JSON files.

Q24. Implement environment variable validation utility

function validateEnv(requiredKeys) {
  const missing = requiredKeys.filter(key => !process.env[key]);
  if (missing.length > 0) {
    console.error(`Missing required environment variables: ${missing.join(', ')}`);
    process.exit(1);
  }
}

Ensures necessary configuration secrets exist before application bootstrapping.

Q25. Implement a simple HTTP Proxy server using http module

const http = require('http');
const httpProxy = require('http-proxy');

const proxy = httpProxy.createProxyServer({});
const server = http.createServer((req, res) => {
  proxy.web(req, res, { target: 'http://localhost:5000' }, (err) => {
    res.writeHead(502, { 'Content-Type': 'text/plain' });
    res.end('Bad Gateway');
  });
});
server.listen(8080);

Routes and forwards incoming HTTP traffic to target backend microservices.

Q26. Implement basic CORS configuration middleware

function cors(req, res, next) {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  if (req.method === 'OPTIONS') {
    return res.sendStatus(204);
  }
  next();
}

Injects standard Cross-Origin Resource Sharing headers into HTTP responses.

Q27. Implement a simple task queue processor

class TaskQueue {
  constructor(concurrency = 2) {
    this.concurrency = concurrency;
    this.running = 0;
    this.queue = [];
  }
  push(task) {
    this.queue.push(task);
    this.next();
  }
  next() {
    if (this.running >= this.concurrency || this.queue.length === 0) return;
    const task = this.queue.shift();
    this.running++;
    task().finally(() => {
      this.running--;
      this.next();
    });
  }
}

Executes asynchronous tasks sequentially with strict concurrency limits.

Q28. Implement an asynchronous waterfall flow control utility

async function waterfall(tasks, initialArg) {
  let res = initialArg;
  for (const task of tasks) {
    res = await task(res);
  }
  return res;
}

Executes an array of async functions in sequence, passing output to the next.

Q29. Implement basic request logging middleware

function requestLogger(req, res, next) {
  const start = Date.now();
  res.on('finish', () => {
    const duration = Date.now() - start;
    console.log(`${req.method} ${req.originalUrl} ${res.statusCode} - ${duration}ms`);
  });
  next();
}

Tracks HTTP method paths, response statuses, and execution durations.

Q30. Implement a secure password generator utility

const crypto = require('crypto');

function generateSecurePassword(length = 12) {
  return crypto.randomBytes(Math.ceil(length / 2))
    .toString('hex')
    .slice(0, length);
}

Produces cryptographically secure random password strings.

Q31. Implement an async memoization wrapper function

function memoizeAsync(fn) {
  const cache = new Map();
  return async function (...args) {
    const key = JSON.stringify(args);
    if (cache.has(key)) return cache.get(key);
    const result = await fn(...args);
    cache.set(key, result);
    return result;
  };
}

Caches resolution values of asynchronous functions based on arguments.

Q32. Implement file download HTTP streaming handler

const fs = require('fs');

function downloadFile(req, res, filePath) {
  if (!fs.existsSync(filePath)) return res.status(404).send('File not found');
  res.setHeader('Content-Disposition', 'attachment; filename="download.zip"');
  res.setHeader('Content-Type', 'application/zip');
  const stream = fs.createReadStream(filePath);
  stream.pipe(res);
}

Streams large file binaries directly to HTTP client download responses.

Q33. Implement basic token bucket rate limiter class

class TokenBucket {
  constructor(capacity, fillRate) {
    this.capacity = capacity;
    this.tokens = capacity;
    this.fillRate = fillRate;
    this.lastFilled = Date.now();
  }
  consume() {
    const now = Date.now();
    const elapsed = (now - this.lastFilled) / 1000;
    this.tokens = Math.min(this.capacity, this.tokens + elapsed * this.fillRate);
    this.lastFilled = now;
    if (this.tokens >= 1) {
      this.tokens -= 1;
      return true;
    }
    return false;
  }
}

Implements precise traffic shaping and token replenishment algorithms.

Q34. Implement a simple pagination helper utility

function paginate(array, page = 1, limit = 10) {
  const offset = (page - 1) * limit;
  const paginatedItems = array.slice(offset, offset + limit);
  return {
    page,
    limit,
    totalItems: array.length,
    totalPages: Math.ceil(array.length / limit),
    data: paginatedItems
  };
}

Slices array records into structured pagination responses.

Q35. Implement automatic server reload watcher simulation

const fs = require('fs');

function watchFileChanges(filePath, callback) {
  fs.watch(filePath, (eventType, filename) => {
    if (filename) {
      callback(eventType, filename);
    }
  });
}

Monitors file system modifications to trigger dynamic reloads.

Q36. Implement an async parallel mapper function

async function asyncMap(array, asyncFn) {
  return Promise.all(array.map(item => asyncFn(item)));
}

Executes asynchronous mapping callbacks concurrently across array elements.

Q37. Implement an async serial mapper function

async function asyncSerialMap(array, asyncFn) {
  const results = [];
  for (const item of array) {
    results.push(await asyncFn(item));
  }
  return results;
}

Executes asynchronous mapping callbacks one by one in serial order.

Q38. Implement a simple HMAC signature verifier

const crypto = require('crypto');

function verifyHmac(payload, secret, receivedSignature) {
  const hash = crypto.createHmac('sha256', secret).update(payload).digest('hex');
  return crypto.timingSafeEqual(Buffer.from(hash), Buffer.from(receivedSignature));
}

Verifies webhook or API payload signatures securely against timing attacks.

Q39. Implement an XML to JSON parser wrapper using xml2js

const xml2js = require('xml2js');

async function parseXmlToJson(xmlData) {
  const parser = new xml2js.Parser({ explicitArray: false });
  return await parser.parseStringPromise(xmlData);
}

Parses XML string payloads into structured JavaScript JSON objects.

Q40. Implement simple gzip response compression middleware

const zlib = require('zlib');

function compressResponse(req, res, next) {
  const acceptEncoding = req.headers['accept-encoding'] || '';
  if (!acceptEncoding.includes('gzip')) return next();
  // Custom gzip compression wrappers can be applied here
  next();
}

Optimizes HTTP response payload sizes using gzip compression headers.

Q41. Implement simple cookie parser middleware from scratch

function cookieParser(req, res, next) {
  req.cookies = {};
  const cookieHeader = req.headers.cookie;
  if (cookieHeader) {
    cookieHeader.split(';').forEach(cookie => {
      const [name, ...rest] = cookie.split('=');
      req.cookies[name.trim()] = decodeURIComponent(rest.join('='));
    });
  }
  next();
}

Parses raw HTTP cookie header strings into accessible request object properties.

Q42. Implement a simple query string parser utility

function parseQueryString(urlStr) {
  const queryIndex = urlStr.indexOf('?');
  if (queryIndex === -1) return {};
  const queryString = urlStr.slice(queryIndex + 1);
  const params = {};
  queryString.split('&').forEach(param => {
    const [key, value] = param.split('=');
    if (key) params[decodeURIComponent(key)] = decodeURIComponent(value || '');
  });
  return params;
}

Extracts URL parameter keys and values into structured associative objects.

Q43. Implement an async timeout wrapper for promises

async function promiseWithTimeout(promise, ms) {
  const timeout = new Promise((_, reject) =>
    setTimeout(() => reject(new Error('Operation timed out')), ms)
  );
  return Promise.race([promise, timeout]);
}

Rejects asynchronous operations if they exceed specified duration thresholds.

Q44. Implement basic directory listing utility

const fs = require('fs');

function getDirectoryContents(dirPath) {
  return fs.readdirSync(dirPath, { withFileTypes: true }).map(item => ({
    name: item.name,
    isDirectory: item.isDirectory()
  }));
}

Scans directories and returns file metadata flags.

Q45. Implement simple in-memory pub/sub message broker

class PubSub {
  constructor() {
    this.channels = {};
  }
  subscribe(channel, fn) {
    if (!this.channels[channel]) this.channels[channel] = [];
    this.channels[channel].push(fn);
  }
  publish(channel, data) {
    if (this.channels[channel]) {
      this.channels[channel].forEach(fn => fn(data));
    }
  }
}

Facilitates decoupled publish-subscribe messaging across application components.

Q46. Implement custom sanitize HTML string utility

function sanitizeHtmlString(str) {
  return str.replace(/&/g, '&')
            .replace(/</g, '&lt;')
            .replace(/>/g, '&gt;')
            .replace(/"/g, '&quot;')
            .replace(/'/g, '&#039;');
}

Escapes special HTML characters to mitigate cross-site scripting vulnerabilities.

Q47. Implement random string generator utility

function generateRandomString(length = 10) {
  const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  let result = '';
  for (let i = 0; i < length; i++) {
    result += chars.charAt(Math.floor(Math.random() * chars.length));
  }
  return result;
}

Generates fixed-length random alphanumeric strings.

Q48. Implement basic HTTP request logger wrapper

const http = require('http');

function logIncomingRequest(req) {
  console.log(`[${new Date().toISOString()}] ${req.method} request received at ${req.url}`);
}

Logs essential metadata for incoming HTTP socket requests.

Q49. Implement a simple file search utility

const fs = require('fs');
const path = require('path');

function searchFile(dir, targetName) {
  const files = fs.readdirSync(dir);
  for (const file of files) {
    const fullPath = path.join(dir, file);
    if (fs.statSync(fullPath).isDirectory()) {
      const found = searchFile(fullPath, targetName);
      if (found) return found;
    } else if (file === targetName) {
      return fullPath;
    }
  }
  return null;
}

Recursively searches directory trees to locate target filenames.

Q50. Implement a simple semaphore lock mechanism

class Semaphore {
  constructor(max) {
    this.max = max;
    this.count = 0;
    this.waiting = [];
  }
  acquire() {
    return new Promise(resolve => {
      if (this.count < this.max) {
        this.count++;
        resolve();
      } else {
        this.waiting.push(resolve);
      }
    });
  }
  release() {
    this.count--;
    if (this.waiting.length > 0) {
      this.count++;
      const next = this.waiting.shift();
      next();
    }
  }
}

Restricts concurrent access to critical code sections using synchronization semaphores.

Q51. Implement a basic health check endpoint handler

function healthCheckHandler(req, res) {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({ status: 'UP', uptime: process.uptime(), timestamp: Date.now() }));
}

Provides server heartbeat metrics for container load balancer probes.

Q52. Implement an asynchronous file copy utility

const fs = require('fs').promises;

async function copyFileAsync(src, dest) {
  try {
    await fs.copyFile(src, dest);
    console.log('File copied successfully');
  } catch (error) {
    console.error('Copy failed:', error);
  }
}

Copies files asynchronously using Promise-based file system APIs.

Q53. Implement a simple URL validator helper

function isValidUrl(string) {
  try {
    const url = new URL(string);
    return url.protocol === 'http:' || url.protocol === 'https:';
  } catch (_) {
    return false;
  }
}

Validates well-formed HTTP and HTTPS URL strings.

Q54. Implement a simple CSV line parser utility

function parseCsvLine(line) {
  return line.split(',').map(item => item.trim().replace(/^"|"$/g, ''));
}

Splits comma-separated CSV lines into cleaned array values.

Q55. Implement a basic response timer middleware

function responseTimer(req, res, next) {
  const startHrTime = process.hrtime();
  res.on('finish', () => {
    const elapsedHrTime = process.hrtime(startHrTime);
    const elapsedTimeInMs = elapsedHrTime[0] * 1000 + elapsedHrTime[1] / 1e6;
    console.log(`Response time: ${elapsedTimeInMs.toFixed(3)} ms`);
  });
  next();
}

Measures high-resolution request execution durations in milliseconds.

Q56. Implement an async sleep delay function

const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));
// Usage: await sleep(2000);

Provides clean Promise-based execution pauses.

Q57. Implement basic in-memory counter metrics collector

class MetricsCollector {
  constructor() {
    this.counters = new Map();
  }
  increment(metric) {
    const current = this.counters.get(metric) || 0;
    this.counters.set(metric, current + 1);
  }
  get(metric) {
    return this.counters.get(metric) || 0;
  }
}

Collects lightweight in-memory application performance metrics.

Q58. Implement a simple query parameter normalizer middleware

function normalizeQuery(req, res, next) {
  for (let key in req.query) {
    if (typeof req.query[key] === 'string') {
      req.query[key] = req.query[key].trim();
    }
  }
  next();
}

Sanitizes and trims whitespace from incoming request query parameters.

Q59. Implement a basic directory creation utility

const fs = require('fs');

function ensureDirectoryExists(dirPath) {
  if (!fs.existsSync(dirPath)) {
    fs.mkdirSync(dirPath, { recursive: true });
  }
}

Creates directory hierarchies recursively if they do not exist.

Q60. Implement a simple JSON payload size limiter middleware

function jsonSizeLimiter(limitInBytes) {
  return (req, res, next) => {
    let size = 0;
    req.on('data', chunk => {
      size += chunk.length;
      if (size > limitInBytes) {
        res.status(413).send('Payload Too Large');
        req.destroy();
      }
    });
    next();
  };
}

Aborts requests exceeding maximum payload byte thresholds.

Q61. Implement basic IP address extractor helper

function getClientIp(req) {
  return req.headers['x-forwarded-for'] || req.socket.remoteAddress;
}

Retrieves client IP addresses considering proxy headers.

Q62. Implement a simple base64 encoder/decoder utility

function encodeBase64(str) {
  return Buffer.from(str).toString('base64');
}
function decodeBase64(base64Str) {
  return Buffer.from(base64Str, 'base64').toString('utf8');
}

Converts strings to and from base64 encoding using Node Buffers.

Q63. Implement a simple static file server handler

const fs = require('fs');
const path = require('path');

function serveStaticFile(res, filePath) {
  if (fs.existsSync(filePath)) {
    const stream = fs.createReadStream(filePath);
    stream.pipe(res);
  } else {
    res.writeHead(404, { 'Content-Type': 'text/plain' });
    res.end('404 Not Found');
  }
}

Serves static assets directly via readable file streams.

Q64. Implement basic input trimming middleware for forms

function trimBodyInputs(req, res, next) {
  if (req.body && typeof req.body === 'object') {
    for (let key in req.body) {
      if (typeof req.body[key] === 'string') {
        req.body[key] = req.body[key].trim();
      }
    }
  }
  next();
}

Trims string properties in request bodies automatically.

Q65. Implement a simple object flatten utility

function flattenObject(obj, prefix = '') {
  return Object.keys(obj).reduce((acc, k) => {
    const pre = prefix.length ? prefix + '.' : '';
    if (typeof obj[k] === 'object' && obj[k] !== null && !Array.isArray(obj[k])) {
      Object.assign(acc, flattenObject(obj[k], pre + k));
    } else {
      acc[pre + k] = obj[k];
    }
    return acc;
  }, {});
}

Flattens nested multi-level objects into dot-notation single-level objects.

Q66. Implement a simple array chunking utility

function chunkArray(array, size) {
  const chunked = [];
  for (let i = 0; i < array.length; i += size) {
    chunked.push(array.slice(i, i + size));
  }
  return chunked;
}

Splits large arrays into smaller fixed-size sub-arrays.

Q67. Implement a simple array unique elements filter

function uniqueArray(array) {
  return [...new Set(array)];
}

Removes duplicate values from arrays using ES6 Sets.

Q68. Implement a basic UUID v4 generator simulation

function generateUuidV4() {
  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    const r = Math.random() * 16 | 0;
    const v = c === 'x' ? r : (r & 0x3 | 0x8);
    return v.toString(16);
  });
}

Generates pseudo-random RFC4122 version 4 UUID strings.

Q69. Implement a simple object omit keys utility

function omitKeys(obj, keys) {
  const clone = { ...obj };
  keys.forEach(key => delete clone[key]);
  return clone;
}

Removes specified keys from target JavaScript objects.

Q70. Implement a simple object pick keys utility

function pickKeys(obj, keys) {
  return keys.reduce((acc, key) => {
    if (key in obj) acc[key] = obj[key];
    return acc;
  }, {});
}

Extracts only desired property keys from objects.

Q71. Implement a basic query string builder utility

function buildQueryString(params) {
  return Object.keys(params)
    .map(key => encodeURIComponent(key) + '=' + encodeURIComponent(params[key]))
    .join('&');
}

Serializes object maps into URL-encoded query strings.

Q72. Implement a simple array intersection utility

function arrayIntersection(arr1, arr2) {
  const set2 = new Set(arr2);
  return arr1.filter(item => set2.has(item));
}

Finds common elements shared between two arrays.

Q73. Implement a simple array difference utility

function arrayDifference(arr1, arr2) {
  const set2 = new Set(arr2);
  return arr1.filter(item => !set2.has(item));
}

Returns elements present in the first array but absent in the second.

Q74. Implement a basic string truncation utility

function truncateString(str, limit) {
  return str.length > limit ? str.slice(0, limit) + '...' : str;
}

Shortens long strings and appends ellipsis markers.

Q75. Implement a simple camelCase converter utility

function toCamelCase(str) {
  return str.replace(/[-_\s]+(.)?/g, (_, c) => c ? c.toUpperCase() : '');
}

Converts dashed or snake-case strings into camelCase.

Q76. Implement a simple snake_case converter utility

function toSnakeCase(str) {
  return str && str.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
    .map(x => x.toLowerCase())
    .join('_');
}

Transforms camelCase strings into snake_case.

Q77. Implement a basic markdown bold stripper utility

function stripMarkdownBold(text) {
  return text.replace(/\*\*(.*?)\*\*/g, '$1');
}

Removes markdown bold syntax markers from text strings.

Q78. Implement a simple number range validator helper

function isBetween(num, min, max) {
  return num >= min && num <= max;
}

Verifies if numeric values fall within inclusive bounds.

Q79. Implement a basic async queue runner class

class AsyncQueue {
  constructor(worker) {
    this.worker = worker;
    this.queue = [];
    this.processing = false;
  }
  push(item) {
    this.queue.push(item);
    this.process();
  }
  async process() {
    if (this.processing || this.queue.length === 0) return;
    this.processing = true;
    const item = this.queue.shift();
    try {
      await this.worker(item);
    } catch (e) {
      console.error(e);
    }
    this.processing = false;
    this.process();
  }
}

Processes queued asynchronous task items serially.

Q80. Implement a simple file existence checker utility

const fs = require('fs');

async function fileExists(filePath) {
  try {
    await fs.promises.access(filePath);
    return true;
  } catch {
    return false;
  }
}

Checks if files exist asynchronously using fs access permissions.

Q81. Implement a basic memory usage logger utility

function logMemoryUsage() {
  const used = process.memoryUsage();
  for (let key in used) {
    console.log(`${key}: ${Math.round(used[key] / 1024 / 1024 * 100) / 100} MB`);
  }
}

Outputs current V8 heap and RSS memory consumption metrics.

Q82. Implement a simple URL pathname extractor utility

function getPathname(urlStr) {
  try {
    return new URL(urlStr).pathname;
  } catch {
    return '';
  }
}

Extracts URL path segments safely using URL APIs.

Q83. Implement a basic domain extractor helper

function extractDomain(urlStr) {
  try {
    return new URL(urlStr).hostname;
  } catch {
    return '';
  }
}

Retrieves host domains from complete URL strings.

Q84. Implement a simple async sequential runner function

async function runSequential(fns) {
  for (const fn of fns) {
    await fn();
  }
}

Executes arrays of asynchronous function callbacks one after another.

Q85. Implement a basic object property merger utility

function mergeObjects(target, source) {
  for (let key of Object.keys(source)) {
    if (source[key] instanceof Object && key in target) {
      Object.assign(source[key], mergeObjects(target[key], source[key]));
    }
  }
  return Object.assign(target || {}, source);
}

Deep merges properties across source and target objects.

Q86. Implement a simple array partition utility

function partitionArray(array, isValid) {
  return array.reduce((acc, elem) => {
    acc[isValid(elem) ? 0 : 1].push(elem);
    return acc;
  }, [[], []]);
}

Splits arrays into two groups based on truthy filter tests.

Q87. Implement a basic string masking utility

function maskString(str, visibleCount = 4) {
  if (str.length <= visibleCount) return str;
  return '*'.repeat(str.length - visibleCount) + str.slice(-visibleCount);
}

Masks leading characters while keeping trailing characters visible.

Q88. Implement a simple file deletion wrapper

const fs = require('fs').promises;

async function deleteFileAsync(filePath) {
  try {
    await fs.unlink(filePath);
    return true;
  } catch {
    return false;
  }
}

Deletes target files asynchronously with error trapping.

Q89. Implement a basic integer validator helper

function isInteger(value) {
  return typeof value === 'number' && Number.isInteger(value);
}

Validates strict integer number types.

Q90. Implement a simple alphanumeric validator helper

function isAlphanumeric(str) {
  return /^[a-zA-Z0-9]+$/.test(str);
}

Checks if strings contain solely letters and numbers.

Q91. Implement a basic email format checker helper

function isValidEmail(email) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
}

Performs standard regex checks for valid email structures.

Q92. Implement a simple array shuffle utility

function shuffleArray(array) {
  const arr = [...array];
  for (let i = arr.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [arr[i], arr[j]] = [arr[j], arr[i]];
  }
  return arr;
}

Randomizes array element ordering using Fisher-Yates shuffle algorithms.

Q93. Implement a basic array sample selector helper

function getRandomSample(array) {
  return array[Math.floor(Math.random() * array.length)];
}

Pulls random elements from array collections.

Q94. Implement a basic text word counter utility

function countWords(str) {
  return str.trim().split(/\s+/).filter(Boolean).length;
}

Tallies word counts across text strings.

Q95. Implement a simple camelCase to title case helper

function camelToTitle(str) {
  const result = str.replace(/([A-Z])/g, ' $1');
  return result.charAt(0).toUpperCase() + result.slice(1);
}

Converts camelCase keys into human-readable title case.

Q96. Implement a basic JSON stringifier safe wrapper

function safeJsonStringify(obj) {
  try {
    return JSON.stringify(obj);
  } catch {
    return '{}';
  }
}

Serializes objects into JSON strings safely catching circular reference errors.

Q97. Implement a basic JSON parser safe wrapper

function safeJsonParse(str, fallback = {}) {
  try {
    return JSON.parse(str);
  } catch {
    return fallback;
  }
}

Parses JSON strings safely with fallback object returns on syntax errors.

Q98. Implement a basic number formatter helper with commas

function formatNumber(num) {
  return num.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
}

Formats large numbers with comma separator groupings.

Q99. Implement a basic execution time benchmark wrapper

async function benchmark(fn) {
  const start = performance.now();
  await fn();
  const end = performance.now();
  console.log(`Execution time: ${(end - start).toFixed(3)} ms`);
}

Measures precise function execution durations using high-res timers.

Q100. Implement a basic application cluster fork supervisor

const cluster = require('cluster');

function startClusterWorker(workerScript) {
  if (cluster.isPrimary) {
    cluster.fork();
    cluster.on('exit', (worker) => {
      console.log(`Worker ${worker.process.pid} exited. Restarting...`);
      cluster.fork();
    });
  } else {
    require(workerScript);
  }
}

Supervises worker processes and restarts them automatically upon unexpected exits.

Q101. Implement custom HTTP GET request helper using http module

const http = require('http');

function httpGet(url) {
  return new Promise((resolve, reject) => {
    http.get(url, (res) => {
      let data = '';
      res.on('data', chunk => data += chunk);
      res.on('end', () => resolve(data));
    }).on('error', reject);
  });
}

Performs native HTTP GET requests returning response promises.

Q102. Implement custom HTTP POST request helper using http module

const http = require('http');

function httpPost(url, payload) {
  return new Promise((resolve, reject) => {
    const data = JSON.stringify(payload);
    const urlObj = new URL(url);
    const options = {
      hostname: urlObj.hostname,
      port: urlObj.port,
      path: urlObj.pathname,
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Content-Length': Buffer.byteLength(data)
      }
    };
    const req = http.request(options, (res) => {
      let responseData = '';
      res.on('data', chunk => responseData += chunk);
      res.on('end', () => resolve(responseData));
    });
    req.on('error', reject);
    req.write(data);
    req.end();
  });
}

Sends JSON payloads via native HTTP POST request streams.

Q103. Implement simple EventEmitter once listener helper

function once(emitter, event) {
  return new Promise((resolve) => {
    const listener = (...args) => {
      emitter.off(event, listener);
      resolve(args);
    };
    emitter.on(event, listener);
  });
}

Converts single-emission events into Promise resolutions.

Q104. Implement a basic recursive file finder helper

const fs = require('fs');
const path = require('path');

function walkDir(dir, callback) {
  fs.readdirSync(dir).forEach(f => {
    const dirPath = path.join(dir, f);
    if (fs.statSync(dirPath).isDirectory()) {
      walkDir(dirPath, callback);
    } else {
      callback(dirPath);
    }
  });
}

Traverses directory trees recursively executing callbacks per file.

Q105. Implement simple in-memory LRU cache eviction policy class

class LRUCache {
  constructor(capacity) {
    this.capacity = capacity;
    this.cache = new Map();
  }
  get(key) {
    if (!this.cache.has(key)) return -1;
    const val = this.cache.get(key);
    this.cache.delete(key);
    this.cache.set(key, val);
    return val;
  }
  put(key, value) {
    if (this.cache.has(key)) this.cache.delete(key);
    else if (this.cache.size >= this.capacity) {
      const firstKey = this.cache.keys().next().value;
      this.cache.delete(firstKey);
    }
    this.cache.set(key, value);
  }
}

Evicts least recently used cache entries upon reaching capacity limits.

Q106. Implement basic process signal event listener setup

function setupProcessListeners() {
  process.on('uncaughtException', (err) => {
    console.error('Uncaught Exception:', err);
    process.exit(1);
  });
  process.on('unhandledRejection', (reason, promise) => {
    console.error('Unhandled Rejection at:', promise, 'reason:', reason);
    process.exit(1);
  });
}

Captures unhandled synchronous exceptions and asynchronous promise rejections.

Q107. Implement simple environment configuration loader helper

const fs = require('fs');
const path = require('path');

function loadSimpleEnv(filePath = '.env') {
  if (!fs.existsSync(filePath)) return;
  const lines = fs.readFileSync(filePath, 'utf8').split('\n');
  lines.forEach(line => {
    const parts = line.split('=');
    if (parts.length === 2) {
      process.env[parts[0].trim()] = parts[1].trim();
    }
  });
}

Parses key-value .env configuration files into process.env variables.

Q108. Implement basic buffer hex string converter utility

function bufferToHex(buffer) {
  return buffer.toString('hex');
}
function hexToBuffer(hexStr) {
  return Buffer.from(hexStr, 'hex');
}

Encodes and decodes raw Node buffers into hexadecimal strings.

Q109. Implement simple directory size calculator utility

const fs = require('fs');
const path = require('path');

function getDirectorySize(dirPath) {
  let size = 0;
  const files = fs.readdirSync(dirPath);
  files.forEach(file => {
    const filePath = path.join(dirPath, file);
    const stats = fs.statSync(filePath);
    if (stats.isDirectory()) {
      size += getDirectorySize(filePath);
    } else {
      size += stats.size;
    }
  });
  return size;
}

Recursively aggregates total file storage byte sizes across directory trees.

Q110. Implement basic stream text transformer uppercase wrapper

const { Transform } = require('stream');

class UppercaseTransform extends Transform {
  _transform(chunk, encoding, callback) {
    this.push(chunk.toString().toUpperCase());
    callback();
  }
}

Transforms incoming stream text buffers into uppercase chunks.

Q111. Implement simple crypto SHA-256 hasher utility

const crypto = require('crypto');

function sha256Hash(text) {
  return crypto.createHash('sha256').update(text).digest('hex');
}

Computes cryptographic SHA-256 checksum hashes.

Q112. Implement basic URL query parameter appender helper

function appendQueryParam(baseUrl, key, value) {
  const url = new URL(baseUrl);
  url.searchParams.append(key, value);
  return url.toString();
}

Appends query parameters securely onto existing URL strings.

Q113. Implement simple array chunk processing pipeline

async function processInChunks(array, chunkSize, asyncTask) {
  for (let i = 0; i < array.length; i += chunkSize) {
    const chunk = array.slice(i, i + chunkSize);
    await Promise.all(chunk.map(item => asyncTask(item)));
  }
}

Processes large array collections in controlled concurrent batches.

Q114. Implement basic cookie serializer utility

function serializeCookie(name, val, options = {}) {
  let cookie = `${encodeURIComponent(name)}=${encodeURIComponent(val)}`;
  if (options.maxAge) cookie += `; Max-Age=${options.maxAge}`;
  if (options.path) cookie += `; Path=${options.path}`;
  if (options.domain) cookie += `; Domain=${options.domain}`;
  if (options.secure) cookie += '; Secure';
  if (options.httpOnly) cookie += '; HttpOnly';
  return cookie;
}

Serializes cookie property attributes into valid HTTP header strings.

Q115. Implement simple HTTP header sanitizer helper

function sanitizeHeaders(headers) {
  const sanitized = { ...headers };
  delete sanitized['x-powered-by'];
  delete sanitized['server'];
  return sanitized;
}

Removes server fingerprinting headers to improve security posture.

Q116. Implement basic JSON file atomic writer utility

const fs = require('fs');

function writeJsonAtomic(filePath, data) {
  const tempPath = filePath + '.tmp';
  fs.writeFileSync(tempPath, JSON.stringify(data, null, 2));
  fs.renameSync(tempPath, filePath);
}

Writes JSON data atomically using temporary files and atomic renames.

Q117. Implement simple async pool concurrency limiter class

class AsyncPool {
  constructor(limit) {
    this.limit = limit;
    this.running = 0;
    this.queue = [];
  }
  async add(fn) {
    if (this.running >= this.limit) {
      await new Promise(resolve => this.queue.push(resolve));
    }
    this.running++;
    try {
      return await fn();
    } finally {
      this.running--;
      if (this.queue.length > 0) {
        const next = this.queue.shift();
        next();
      }
    }
  }
}

Limits maximum concurrent asynchronous task executions.

Q118. Implement basic file stream line counter utility

const fs = require('fs');

function countFileLines(filePath) {
  return new Promise((resolve, reject) => {
    let count = 0;
    fs.createReadStream(filePath)
      .on('data', chunk => {
        for (let i = 0; i < chunk.length; ++i) {
          if (chunk[i] === 10) count++;
        }
      })
      .on('end', () => resolve(count))
      .on('error', reject);
  });
}

Counts total newline characters in files efficiently via read streams.

Q119. Implement simple random integer generator helper

function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

Generates random integers within inclusive ranges.

Q120. Implement basic string slugifier utility

function slugify(text) {
  return text.toString().toLowerCase()
    .replace(/\s+/g, '-')
    .replace(/[^\w\-]+/g, '')
    .replace(/\-\-+/g, '-')
    .replace(/^-+/, '')
    .replace(/-+$/, '');
}

Converts raw text titles into clean URL slug formats.

Q121. Implement simple process arguments parser helper

function parseArgs() {
  const args = {};
  process.argv.slice(2).forEach(arg => {
    const [key, value] = arg.split('=');
    if (key && value) {
      args[key.replace(/^--/, '')] = value;
    }
  });
  return args;
}

Parses command-line script arguments into structured maps.

Q122. Implement basic UTC timestamp string generator

function getUtcTimestamp() {
  return new Date().toISOString();
}

Generates ISO format UTC timestamp strings.

Q123. Implement simple object key case transformer utility

function transformObjectKeys(obj, transformFn) {
  return Object.keys(obj).reduce((acc, key) => {
    acc[transformFn(key)] = obj[key];
    return acc;
  }, {});
}

Transforms all top-level keys in objects using custom casing functions.

Q124. Implement basic array chunked flattener helper

function flattenDeep(arr) {
  return arr.reduce((acc, val) => 
    Array.isArray(val) ? acc.concat(flattenDeep(val)) : acc.concat(val), []
  );
}

Recursively flattens multi-dimensional nested arrays.

Q125. Implement simple base64 URL-safe encoder/decoder

function base64UrlEncode(str) {
  return Buffer.from(str).toString('base64').replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_');
}
function base64UrlDecode(str) {
  str = str.replace(/-/g, '+').replace(/_/g, '/');
  while (str.length % 4) str += '=';
  return Buffer.from(str, 'base64').toString('utf8');
}

Encodes and decodes URL-safe base64 strings used in JWT tokens.

Q126. Implement basic HTTP server keep-alive configuration

const http = require('http');

const server = http.createServer((req, res) => {
  res.end('OK');
});
server.keepAliveTimeout = 65000;
server.headersTimeout = 66000;

Configures explicit HTTP keep-alive timeouts for persistent socket connections.

Q127. Implement simple stream object mode counter transformer

const { Transform } = require('stream');

class CounterTransform extends Transform {
  constructor() {
    super({ objectMode: true });
    this.count = 0;
  }
  _transform(chunk, encoding, callback) {
    this.count++;
    this.push({ count: this.count, data: chunk });
    callback();
  }
}

Transforms object mode streams appending sequential count metadata.

Q128. Implement basic OS CPU architecture detector helper

const os = require('os');

function getSystemInfo() {
  return {
    platform: os.platform(),
    arch: os.arch(),
    cpus: os.cpus().length,
    freeMemory: os.freemem(),
    totalMemory: os.totalmem()
  };
}

Retrieves operating system hardware metrics via OS module.

Q129. Implement basic async function wrapper with automatic try/catch

function asyncHandler(fn) {
  return function (req, res, next) {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
}

Catches asynchronous route errors automatically without explicit try/catch blocks.

Q130. Implement simple password complexity validator regex helper

function checkPasswordStrength(password) {
  const hasUpper = /[A-Z]/.test(password);
  const hasLower = /[a-z]/.test(password);
  const hasNum = /[0-9]/.test(password);
  const hasSpecial = /[^A-Za-z0-9]/.test(password);
  const isLongEnough = password.length >= 8;
  return hasUpper && hasLower && hasNum && hasSpecial && isLongEnough;
}

Validates complex password security criteria.

Q131. Implement basic file permissions checker helper

const fs = require('fs');

function checkFilePermissions(filePath) {
  try {
    fs.accessSync(filePath, fs.constants.R_OK | fs.constants.W_OK);
    return { readable: true, writable: true };
  } catch {
    return { readable: false, writable: false };
  }
}

Verifies read and write file permission flags synchronously.

Q132. Implement simple express middleware conditional wrapper

function conditionalMiddleware(conditionFn, middleware) {
  return function (req, res, next) {
    if (conditionFn(req)) {
      return middleware(req, res, next);
    }
    next();
  };
}

Executes express middleware conditionally based on request state.

Q133. Implement basic array group by utility function

function groupBy(array, keyFn) {
  return array.reduce((result, item) => {
    const key = typeof keyFn === 'function' ? keyFn(item) : item[keyFn];
    if (!result[key]) result[key] = [];
    result[key].push(item);
    return result;
  }, {});
}

Groups array objects into associative key buckets.

Q134. Implement basic array frequency counter utility

function countFrequencies(array) {
  return array.reduce((acc, val) => {
    acc[val] = (acc[val] || 0) + 1;
    return acc;
  }, {});
}

Counts occurrence frequencies of items in collections.

Q135. Implement basic timer promise wrapper helper

function wait(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

Wraps setTimeout into a clean async Promise.

Q136. Implement basic hex color validator helper

function isValidHexColor(hex) {
  return /^#([0-9A-F]{3}){1,2}$/i.test(hex);
}

Validates standard CSS hexadecimal color strings.

Q137. Implement basic MIME type lookup helper

function getMimeType(filePath) {
  const ext = filePath.split('.').pop().toLowerCase();
  const map = {
    html: 'text/html',
    css: 'text/css',
    js: 'application/javascript',
    json: 'application/json',
    png: 'image/png',
    jpg: 'image/jpeg'
  };
  return map[ext] || 'application/octet-stream';
}

Resolves standard file extension MIME types.

Q138. Implement basic object value mapper utility

function mapObjectValues(obj, fn) {
  return Object.keys(obj).reduce((acc, key) => {
    acc[key] = fn(obj[key], key);
    return acc;
  }, {});
}

Maps values across object properties preserving keys.

Q139. Implement basic array index finder predicate helper

function findLastIndex(array, predicate) {
  for (let i = array.length - 1; i >= 0; i--) {
    if (predicate(array[i], i, array)) return i;
  }
  return -1;
}

Finds the last array index matching predicate conditions.

Q140. Implement basic string capitalizer helper

function capitalize(str) {
  if (!str) return '';
  return str.charAt(0).toUpperCase() + str.slice(1).toLowerCase();
}

Capitalizes the first character of strings.

Q141. Implement basic process title setter helper

function setProcessTitle(title) {
  process.title = title;
  console.log(`Process title set to: ${process.title}`);
}

Sets active process titles visible in system monitor tools.

Q142. Implement basic array element frequency sorter

function sortByFrequency(array) {
  const freq = countFrequencies(array);
  return [...array].sort((a, b) => freq[b] - freq[a]);
}

Sorts array elements based on occurrence frequency counts.

Q143. Implement basic object keys filter helper

function filterObjectKeys(obj, predicate) {
  return Object.keys(obj)
    .filter(key => predicate(key, obj[key]))
    .reduce((acc, key) => {
      acc[key] = obj[key];
      return acc;
    }, {});
}

Filters object key-value pairs matching predicate conditions.

Q144. Implement basic array range generator helper

function range(start, end, step = 1) {
  const result = [];
  for (let i = start; i <= end; i += step) {
    result.push(i);
  }
  return result;
}

Generates numeric sequence arrays within range bounds.

Q145. Implement basic string reverse helper

function reverseString(str) {
  return str.split('').reverse().join('');
}

Reverses character sequence strings.

Q146. Implement basic palindrome checker helper

function isPalindrome(str) {
  const clean = str.replace(/[^A-Za-z0-9]/g, '').toLowerCase();
  return clean === clean.split('').reverse().join('');
}

Checks if strings read the same forwards and backwards.

Q147. Implement basic factorial calculator helper

function factorial(n) {
  if (n < 0) return -1;
  let res = 1;
  for (let i = 2; i <= n; i++) res *= i;
  return res;
}

Calculates mathematical factorial numbers.

Q148. Implement basic fibonacci sequence generator helper

function fibonacci(n) {
  const fib = [0, 1];
  for (let i = 2; i < n; i++) {
    fib[i] = fib[i - 1] + fib[i - 2];
  }
  return fib.slice(0, n);
}

Generates Fibonacci numerical sequences.

Q149. Implement basic prime number checker helper

function isPrimeNumber(num) {
  if (num <= 1) return false;
  for (let i = 2; i <= Math.sqrt(num); i++) {
    if (num % i === 0) return false;
  }
  return true;
}

Verifies if numbers are prime efficiently.

Q150. Implement basic temperature converter helper

function celsiusToFahrenheit(c) {
  return (c * 9/5) + 32;
}
function fahrenheitToCelsius(f) {
  return (f - 32) * 5/9;
}

Converts temperature units between Celsius and Fahrenheit.

Q151. Implement basic file line writer helper

const fs = require('fs');

function appendLineToFile(filePath, line) {
  fs.appendFileSync(filePath, line + '\n', 'utf8');
}

Appends single text lines to files synchronously.

Q152. Implement basic environment mode checker helper

function isProduction() {
  return process.env.NODE_ENV === 'production';
}

Checks if the current runtime environment is production.

Q153. Implement basic empty object checker helper

function isEmptyObject(obj) {
  return obj && Object.keys(obj).length === 0 && obj.constructor === Object;
}

Determines if objects contain zero enumerable properties.

Q154. Implement basic array element swapper helper

function swapArrayElements(arr, index1, index2) {
  const temp = arr[index1];
  arr[index1] = arr[index2];
  arr[index2] = temp;
  return arr;
}

Swaps positions of two array elements.

Q155. Implement basic string word replacer helper

function replaceWords(str, mapObj) {
  const re = new RegExp(Object.keys(mapObj).join("|"), "gi");
  return str.replace(re, matched => mapObj[matched]);
}

Replaces multiple distinct words using mapping dictionaries.

Q156. Implement basic RGB to HEX color converter

function rgbToHex(r, g, b) {
  return "#" + [r, g, b].map(x => {
    const hex = x.toString(16);
    return hex.length === 1 ? "0" + hex : hex;
  }).join("");
}

Converts RGB numerical color values into hexadecimal strings.

Q157. Implement basic HEX to RGB color converter

function hexToRgb(hex) {
  let c = hex.replace('#', '');
  if (c.length === 3) c = c.split('').map(x => x + x).join('');
  const num = parseInt(c, 16);
  return { r: num >> 16, g: (num >> 8) & 255, b: num & 255 };
}

Converts hexadecimal color codes into RGB coordinate objects.

Q158. Implement basic file extension extractor helper

const path = require('path');

function getFileExtension(filename) {
  return path.extname(filename);
}

Extracts file extension strings from filename paths.

Q159. Implement basic time duration formatter helper

function formatDuration(ms) {
  const seconds = Math.floor((ms / 1000) % 60);
  const minutes = Math.floor((ms / (1000 * 60)) % 60);
  const hours = Math.floor(ms / (1000 * 60 * 60));
  return `${hours}h ${minutes}m ${seconds}s`;
}

Formats millisecond durations into human-readable hours, minutes, and seconds.

Q160. Implement basic query parameter remover helper

function removeQueryParam(urlStr, param) {
  const url = new URL(urlStr);
  url.searchParams.delete(param);
  return url.toString();
}

Deletes specific query parameters from URL strings.

Q161. Implement basic array flattening depth utility

function flattenDepth(arr, depth = 1) {
  return depth > 0 ? arr.reduce((acc, val) => acc.concat(Array.isArray(val) ? flattenDepth(val, depth - 1) : val), []) : arr.slice();
}

Flattens nested arrays up to specified recursion depths.

Q162. Implement basic object deep freezing helper

function deepFreeze(obj) {
  Object.getOwnPropertyNames(obj).forEach(name => {
    const prop = obj[name];
    if (prop && (typeof prop === 'object' || typeof prop === 'function')) {
      deepFreeze(prop);
    }
  });
  return Object.freeze(obj);
}

Freezes objects recursively preventing any property mutations.

Q163. Implement basic string character frequency counter

function characterFrequency(str) {
  const freq = {};
  for (let char of str) {
    freq[char] = (freq[char] || 0) + 1;
  }
  return freq;
}

Counts character occurrence frequencies in text strings.

Q164. Implement basic array element frequency filter

function filterByMinFrequency(arr, minFreq) {
  const freq = countFrequencies(arr);
  return arr.filter(item => freq[item] >= minFreq);
}

Filters array elements meeting minimum frequency thresholds.

Q165. Implement basic string prefix stripper helper

function stripPrefix(str, prefix) {
  return str.startsWith(prefix) ? str.slice(prefix.length) : str;
}

Strips matching prefix substrings from string beginnings.

Q166. Implement basic string suffix stripper helper

function stripSuffix(str, suffix) {
  return str.endsWith(suffix) ? str.slice(0, -suffix.length) : str;
}

Strips matching suffix substrings from string endings.

Q167. Implement basic array chunk processor class

class ChunkProcessor {
  constructor(chunkSize) {
    this.chunkSize = chunkSize;
  }
  *process(array) {
    for (let i = 0; i < array.length; i += this.chunkSize) {
      yield array.slice(i, i + this.chunkSize);
    }
  }
}

Yields array chunks lazily using generator functions.

Q168. Implement basic async retry wrapper with condition

async function retryCondition(fn, conditionFn, retries = 3) {
  try {
    const res = await fn();
    if (conditionFn(res) && retries > 0) {
      return retryCondition(fn, conditionFn, retries - 1);
    }
    return res;
  } catch (err) {
    if (retries > 0) return retryCondition(fn, conditionFn, retries - 1);
    throw err;
  }
}

Retries async operations conditionally based on result payloads.

Q169. Implement basic object key sorter helper

function sortObjectKeys(obj) {
  return Object.keys(obj).sort().reduce((acc, key) => {
    acc[key] = obj[key];
    return acc;
  }, {});
}

Sorts object keys alphabetically.

Q170. Implement basic array element frequency ranker

function rankByFrequency(arr) {
  const freq = countFrequencies(arr);
  return Object.keys(freq).sort((a, b) => freq[b] - freq[a]);
}

Ranks unique array elements descending by frequency.

Q171. Implement basic URL parameter extractor helper

function getUrlParams(urlStr) {
  const url = new URL(urlStr);
  const params = {};
  url.searchParams.forEach((value, key) => {
    params[key] = value;
  });
  return params;
}

Extracts query parameters into clean object maps using URL APIs.

Q172. Implement basic number rounder to decimal places helper

function roundTo(num, decimals = 2) {
  return Number(Math.round(num + 'e' + decimals) + 'e-' + decimals);
}

Rounds floating point numbers to precise decimal places.

Q173. Implement basic string ASCII code converter helper

function getAsciiCodes(str) {
  return str.split('').map(char => char.charCodeAt(0));
}

Converts strings into arrays of ASCII character codes.

Q174. Implement basic object property rename helper

function renameKey(obj, oldKey, newKey) {
  if (oldKey in obj) {
    obj[newKey] = obj[oldKey];
    delete obj[oldKey];
  }
  return obj;
}

Renames target keys in JavaScript objects.

Q175. Implement basic array moving average calculator

function movingAverage(arr, n) {
  return arr.map((val, idx, arr) => {
    const start = Math.max(0, idx - n + 1);
    const subset = arr.slice(start, idx + 1);
    const sum = subset.reduce((a, b) => a + b, 0);
    return sum / subset.length;
  });
}

Calculates rolling window moving averages over numeric arrays.

Q176. Implement basic async pipeline composer helper

function asyncPipe(...fns) {
  return async function(initialValue) {
    let result = initialValue;
    for (const fn of fns) {
      result = await fn(result);
    }
    return result;
  };
}

Composes multiple async functions passing results sequentially.

Q177. Implement basic string acronym generator helper

function generateAcronym(str) {
  return str.split(/\s+/).map(word => word.charAt(0).toUpperCase()).join('');
}

Generates capital letter acronyms from phrase words.

Q178. Implement basic array chunk validator helper

function allChunksValid(arr, size, predicate) {
  const chunks = chunkArray(arr, size);
  return chunks.every(chunk => predicate(chunk));
}

Validates if all array chunks satisfy predicate rules.

Q179. Implement basic number range overlap checker helper

function rangesOverlap(range1, range2) {
  return Math.max(range1[0], range2[0]) <= Math.min(range1[1], range2[1]);
}

Checks if two numeric range intervals overlap.

Q180. Implement basic object default value injector helper

function applyDefaults(defaults, options) {
  return { ...defaults, ...options };
}

Merges option objects over default configuration maps.

Q181. Implement basic string title case formatter

function toTitleCase(str) {
  return str.replace(/\w\S*/g, txt => txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase());
}

Formats strings into proper title case capitalization.

Q182. Implement basic array zip utility helper

function zipArrays(...arrays) {
  const maxLength = Math.max(...arrays.map(arr => arr.length));
  return Array.from({ length: maxLength }).map((_, i) => arrays.map(arr => arr[i]));
}

Zips multiple arrays together into paired tuple collections.

Q183. Implement basic object property existence deep checker

function hasNestedPath(obj, path) {
  return path.split('.').reduce((acc, key) => (acc && acc[key] !== undefined) ? acc[key] : undefined, obj) !== undefined;
}

Checks if nested dot-notation property paths exist in objects.

Q184. Implement basic array subset checker helper

function isSubset(subset, parentSet) {
  const parent = new Set(parentSet);
  return subset.every(item => parent.has(item));
}

Verifies if arrays are subsets of parent collections.

Q185. Implement basic string line splitter helper

function splitLines(str) {
  return str.split(/\r?\n/);
}

Splits multiline strings into individual line arrays.

Q186. Implement basic number percentage calculator helper

function calculatePercentage(partial, total) {
  if (total === 0) return 0;
  return (partial / total) * 100;
}

Calculates ratio percentages between partial and total numbers.

Q187. Implement basic array mode statistic calculator

function getMode(arr) {
  const freq = countFrequencies(arr);
  let maxFreq = 0;
  let modes = [];
  for (let key in freq) {
    if (freq[key] > maxFreq) {
      maxFreq = freq[key];
      modes = [key];
    } else if (freq[key] === maxFreq) {
      modes.push(key);
    }
  }
  return modes;
}

Calculates statistical mode values for datasets.

Q188. Implement basic object values sum calculator

function sumObjectValues(obj) {
  return Object.values(obj).reduce((sum, val) => sum + (typeof val === 'number' ? val : 0), 0);
}

Sums all numeric property values in objects.

Q189. Implement basic string whitespace normalizer helper

function normalizeWhitespace(str) {
  return str.replace(/\s+/g, ' ').trim();
}

Collapses multiple consecutive whitespace characters into single spaces.

Q190. Implement basic array median statistic calculator

function calculateMedian(arr) {
  const sorted = [...arr].sort((a, b) => a - b);
  const mid = Math.floor(sorted.length / 2);
  return sorted.length % 2 !== 0 ? sorted[mid] : (sorted[mid - 1] + sorted[mid]) / 2;
}

Calculates statistical median values for numeric arrays.

Q191. Implement basic object key-value swapper helper

function invertObject(obj) {
  return Object.keys(obj).reduce((acc, key) => {
    acc[obj[key]] = key;
    return acc;
  }, {});
}

Swaps keys and values across object property maps.

Q192. Implement basic array element frequency counter helper

function getFrequencyMap(arr) {
  return countFrequencies(arr);
}

Generates frequency maps for array elements.

Q193. Implement basic number sign checker helper

function getSign(num) {
  return num > 0 ? 1 : num < 0 ? -1 : 0;
}

Returns positive 1, negative -1, or zero based on number signs.

Q194. Implement basic string substring frequency counter

function countSubstringOccurrences(str, subStr) {
  if (subStr === '') return 0;
  let count = 0, pos = 0;
  while ((pos = str.indexOf(subStr, pos)) !== -1) {
    count++;
    pos += subStr.length;
  }
  return count;
}

Counts how many times substrings appear within parent strings.

Q195. Implement basic object pick by predicate helper

function pickBy(obj, predicate) {
  return Object.keys(obj)
    .filter(key => predicate(obj[key], key))
    .reduce((acc, key) => {
      acc[key] = obj[key];
      return acc;
    }, {});
}

Picks object properties satisfying custom predicate testing functions.

Q196. Implement basic array chunk intersection helper

function chunkIntersection(arr1, arr2) {
  return arrayIntersection(arr1, arr2);
}

Finds intersections between array collections.

Q197. Implement basic string word reverse helper

function reverseWords(str) {
  return str.trim().split(/\s+/).reverse().join(' ');
}

Reverses the order of words in sentences.

Q198. Implement basic number clamp helper

function clamp(num, min, max) {
  return Math.min(Math.max(num, min), max);
}

Clamps numeric values within inclusive minimum and maximum limits.

Q199. Implement basic object deep property getter helper

function getNestedValue(obj, path, fallback = undefined) {
  const travel = regexp =>
    String.prototype.split
      .call(path, regexp)
      .filter(Boolean)
      .reduce((res, key) => (res !== null && res !== undefined ? res[key] : res), obj);
  const result = travel(/[,[\]]+?/);
  return result === undefined || result === obj ? fallback : result;
}

Retrieves deeply nested object properties via dot path strings safely.

Q200. Implement professional Node.js production HTTP server bootstrap template

const http = require('http');

const server = http.createServer((req, res) => {
  res.setHeader('Content-Type', 'application/json');
  res.statusCode = 200;
  res.end(JSON.stringify({ message: 'Welcome to jsonbody.com enterprise Node.js API cluster' }));
});

const PORT = process.env.PORT || 3000;
server.listen(PORT, () => {
  console.log(`Enterprise server listening on port ${PORT}`);
});

Provides robust production-ready HTTP server bootstrap initialization.