Node.js Interview Questions for Freshers

scripts maps short names to shell commands, so the team runs npm run dev instead of remembering long commands. npm adds node_modules/.bin to the path, so locally installed tools like jest or tsc work without a global install. start and test can be run without run. Dependencies live in dependencies, not here.

require runs the module once, caches it, and returns its module.exports object. Anything not attached to module.exports stays private to the file. A common bug is writing exports = { ... }, which only reassigns the local shortcut and breaks the link; use module.exports = { ... } or add properties with exports.name = ....

False. __dirname, __filename and require are CommonJS module wrappers and don't exist in ES modules. In ESM use import.meta.dirname and import.meta.filename (available in current Node.js releases), or derive them from import.meta.url with fileURLToPath. This trips people up when they switch a project to "type": "module".

process.argv is an array of strings: index 0 is the path to the Node.js executable, index 1 is the script path, and your own arguments start at index 2. So process.argv[2] is "hello". For real command-line tools, Node's built-in util.parseArgs handles flags and options so you don't parse the array by hand.

path.join joins the segments with the platform's separator and then normalises the result, resolving .. and .. So /a/b/../c becomes /a/c. Build file paths with path.join or path.resolve rather than string concatenation, which breaks on Windows and leaves double slashes behind.

http.createServer((req, res) => { ... }) gives you a request handler, and server.listen(3000) starts it. Frameworks like Express are built on top of it. net is lower-level raw TCP, fs is for files, and url parses addresses. The node: prefix makes it clear you mean the built-in module, not an npm package with the same name.

Node.js provides process, Buffer, timers, console and, in CommonJS, require and module. window and document are browser APIs for pages and don't exist in Node.js; the global object is globalThis. Code shared between browser and server should check for these before using them.

Runtime packages such as Express go in dependencies. Tools you only need while developing, such as test runners, linters and TypeScript, go in devDependencies. A production install with npm ci --omit=dev skips the dev ones, giving smaller images and fewer packages that could carry vulnerabilities.

The promise versions don't block the event loop, so prefer them in servers. writeFile overwrites by default; use appendFile to add. existsSync is fine in startup code, but checking then reading creates a race, so it's usually better to just try the operation and handle ENOENT. recursive: true also stops mkdir failing if the folder exists.

npx runs a package binary. If the project has it in node_modules, that copy runs; otherwise npx can fetch it temporarily, which is handy for one-off generators. It avoids global installs, which drift between machines. Be careful running unfamiliar package names with npx: a typo can execute someone else's code.