Essential Core Modules in Node.js

Back to Node.js
Arjit Sharma
02 Mins

Node.js comes with a rich set of built-in (core) modules that let you work with files, paths, URLs, operating system data, and networking. Core modules are built into Node.js and do not require installation via npm.

ModulePurpose
httpCreate web servers
fsFile system operations
pathPath manipulation
urlParse and format URLs
osGet system info
eventsEvent-driven architecture
processControl runtime & env vars
cryptoHashing and encryption utilities

Working with File System (fs)

Node’s fs module lets you read and write files.

const fs = require("node:fs");
const fs_p = require("fs/promises");

// Write file
fs.writeFile("hello.txt", "Hello, FileSystem!", (err) => {
  if (err) throw err;
  console.log("File saved!");
});

// Read file
fs.readFile("hello.txt", "utf8", (err, data) => {
  if (err) throw err;
  console.log(data);
});

// Read file (Promises) - Modern Node versions support promise-based file operations:
async function readFilePromise() {
  const data = await fs_p.readFile("hello.txt", "utf8");
  console.log(data);
}

Note - For large files, streaming (fs.createReadStream) is preferred over readFile to avoid high memory usage.

Path Module (path)

File paths differ between operating systems (/ vs ). The path module ensures your code works everywhere

const path = require("path");

// __dirname gives the absolute path of the current file’s directory.
const fullPath = path.join(__dirname, "public", "index.html");
console.log(fullPath);
console.log(path.extname(fullPath)); // '.html'

Commonly used methods:

  • path.join()
  • path.resolve()
  • path.extname()
  • path.basename()

URL Parsing (url)

Break down URLs into useful components. This is especially useful when building APIs or routing logic.

const { URL } = require("url");

const myUrl = new URL("http://localhost:3000/search?name=Arjit&age=25");

console.log(myUrl.pathname);                 // '/search'
console.log(myUrl.searchParams.get("name")); // 'Arjit'

In modern Node.js, URL is globally available, so you can use it directly without importing.

MIME Type Handling

When serving files, browsers need to know what kind of content they’re receiving.

This is done using MIME types. Node.js does not automatically determine MIME types when serving files, so external libraries are commonly used.

npm install mime-types

const mime = require("mime-types");

console.log(mime.lookup("index.html")); // 'text/html'
console.log(mime.contentType("json"));  // 'application/json'

// If mime.lookup() fails, it can return false.
 mime.lookup(filePath) || "application/octet-stream";

MIME types ensure: HTML renders correctly, JSON is parsed properly, Images and videos display as expected

Putting It Together: Serving a File

Here’s a simple example combining fs, path, and MIME types:

const http = require("http");
const fs = require("fs");
const path = require("path");
const mime = require("mime-types");

const server = http.createServer((req, res) => {
  const filePath = path.join(__dirname, "public", "index.html");
  const contentType = mime.lookup(filePath);

  fs.readFile(filePath, (err, content) => {
    if (err) {
      res.writeHead(500);
      res.end("Server Error");
      return;
    }

    res.writeHead(200, { "Content-Type": contentType });
    res.end(content);
  });
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});
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