What is the purpose of `__dirname` and `__filename` in Node.js?

Q: What is the purpose of `__dirname` and `__filename` in Node.js?

**Target Audience:** Engineers preparing for Node.js phone screens — assumes very basic file-path familiarity. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term: . The values below were printed from a **real file on disk**, deliberately not from `node -e`, which was checked first and produces misleading placeholder values instead. ## 1. Why This Even Matters — A Story First A person gives directions as "the store two blocks from here" — which only makes sense if "here" is fixed and known. If "here" secretly means "wherever the person happens to be standing when they say it," the same sentence points to a different store every time depending on where the speaker was standing, which is exactly the bug a relative file path has when it silently depends on the process's launch directory instead of the file's own location. ## 2. The Core Idea 📌 **Interview term:** `__dirname` and `__filename`

01

Understand the problem

Question presented to candidate: "Your code does fs.readFileSync('./config.json') and it works when you run it from the project root, but breaks when a teammate runs it from a different directory. What went wrong, and what should you have used instead?"

What a strong answer should cover:

__dirname and __filename are two of the five parameters supplied by Node's implicit CommonJS module wrapper — the current module file's absolute directory path and absolute file path, respectively.
📌 The bug they fix: a relative path like ./config.json is resolved against the process's current working directory (wherever the node command was actually invoked from), not against the file's own location. path.join(__dirname, "config.json") is resolved against the file's own location, which is what most code actually means when it says "the config file next to me."
__dirname/__filename exist only in CommonJS files — in an ES Module, there is no such implicit variable; the equivalent is derived from import.meta.url (typically via fileURLToPath(import.meta.url) and path.dirname(...) of that).
Running code with node -e "..." or via the REPL produces misleading placeholder values for these (. and [eval]) rather than a real path — a good answer notes this rather than testing/demonstrating the concept that way and drawing the wrong conclusion from it.
process.cwd() is the commonly confused alternative — it returns the current working directory of the process, which changes based on how and from where the script was launched, and is a fundamentally different, session-dependent value from a file's own fixed location.
A precise answer names the practical rule: any path meant to be relative to the source file itself (a config file shipped next to the code, a template, a static asset) should be built with __dirname/import.meta.url, never a bare relative string — those are the correct tool only for a path meant to be relative to wherever the process happens to be invoked from.

Clarifying questions expected:

"Is this CommonJS or an ES Module?" — the mechanism (implicit variable vs. import.meta.url) differs.
"Does the path actually need to be relative to the invoking directory, or to the source file?" — this is the real distinction the bug in the prompt is about.

Code / implementation expected: Yes — showing the actual absolute values from a real file, and the ESM equivalent via import.meta.url, is the concrete deliverable.

global variablespathsmodulescommonjs

02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

Target Audience: Engineers preparing for Node.js phone screens — assumes very basic file-path familiarity. Difficulty: Easy

How to read this doc: Concepts are explained in plain language first, then tagged with 📌 Interview term:. The values below were printed from a real file on disk, d

Solution ready — 2 min read

Classified // press E to declassify

04

Read the code

Real __dirname/__filename values from an actual file, the bug they fix, and the ESM equivalent

// dirtest.cjs — run as: node dirtest.cjs
console.log("__dirname:", __dirname);
console.log("__filename:", __filename);
// __dirname: C:\...\node-batch5
// __filename: C:\...\node-batch5\dirtest.cjs

// BROKEN — depends on wherever "node" was invoked from:
const data = fs.readFileSync("./config.json");
// CORRECT — anchored to this file's own fixed location:
const data2 = fs.readFileSync(path.join(__dirname, "config.json"));

// The ES Modules equivalent (no __dirname/__filename there):
import { fileURLToPath } from "node:url";
import path from "node:path";
const __filenameESM = fileURLToPath(import.meta.url);
const __dirnameESM = path.dirname(__filenameESM);

05

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What is the purpose of `dirname` and `filename` in Node.js?

Understand the problem

Attempt it yourself

Study the solution

Solution ready — 2 min read

Read the code

Join the discussion

Discussion (0)

KEEP THE
STREAK ALIVE.

Understand the problem

Attempt it yourself

Study the solution

Solution ready — 2 min read

Read the code

Join the discussion

Discussion (0)

KEEP THESTREAK ALIVE.

KEEP THE
STREAK ALIVE.