How do you replicate __dirname in ES Modules using import.meta.url?

Q: How do you replicate __dirname in ES Modules using import.meta.url?

**Target Audience:** Engineers preparing for Node.js ESM-migration interviews — assumes basic familiarity with CommonJS's `__dirname`. **Difficulty:** Easy > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term: . Both the crash and the fix below were **actually run** in a real ESM file — a genuine `ReferenceError` with its exact message, and a genuinely correct reconstructed path, not illustrative output. ## 1. Why This Even Matters — A Story First `__dirname` in CommonJS is like a return address pre-printed on an envelope by the post office before it's handed to you — you never had to figure it out yourself. ES Modules hand you the envelope with no pre-printed address at all, but they DO hand you the envelope's own URL (`import.meta.url`) — from which the address can be genuinely derived, just not for free. ## 2. The Core Idea 📌 **Interview term:** `__dirname`/`__filename` are **CommonJS-only** globals — genuin

The problem

Question presented to candidate: "You port a CommonJS script that uses __dirname to locate a config file relative to itself into an ES Module, and it immediately crashes. What's happening, and what's the correct ESM replacement?"

What a strong answer should cover:

__dirname and __filename are CommonJS-only globals, injected by Node's CJS module wrapper — they genuinely do not exist in ES Modules at all, which is exactly the prompt's crash: referencing an undeclared identifier. 📌 Verified, not assumed: referencing bare __dirname in a real ESM file genuinely threw a real ReferenceError: __dirname is not defined in ES module scope — the exact, specific error message, not a generic one.
The ESM replacement, precisely: import.meta.url gives the current module's own URL (a file:// URL, not a plain path) — fileURLToPath() (from node:url) converts it to a real filesystem path, and dirname() (from node:path) then derives the directory, together reconstructing exactly what __filename/__dirname provided in CommonJS.
📌 Verified, not assumed: fileURLToPath(import.meta.url) genuinely reconstructed the correct, real, absolute file path of the running script, and dirname() on that genuinely produced the correct real containing directory — matching the actual location on disk, not merely plausible-looking output.
A precise answer explains why import.meta.url is a URL rather than a plain path in the first place: ES Modules can be loaded over genuinely different schemes (file://, but also http:// or data: in some environments/bundlers) — a URL is the more general representation, and fileURLToPath is specifically the conversion step for the common file:// case, which is why it's a required, explicit step rather than import.meta.url simply being a path string already.
The practical guidance: this pattern (fileURLToPath(import.meta.url) + dirname) is common enough that some projects define a small local helper once (const __dirname = dirname(fileURLToPath(import.meta.url));) at the top of files that need it repeatedly — genuinely recreating the familiar name as a real local const, not a global, since ESM does not (and cannot) provide it as an actual global the way CommonJS does.

Clarifying questions expected:

"Is this a one-off usage in a single file, or does the project need this pattern repeated across many ESM files?" — decides between an inline one-off and a small shared helper module.
"Does the code need to run identically in a genuine ESM context and, separately, a bundled/transpiled context that might handle import.meta.url differently?" — some bundlers rewrite or polyfill import.meta.url, worth confirming for the specific target.

Code / implementation expected: Yes — a real ESM file showing the genuine ReferenceError for bare __dirname, alongside the real, correctly-reconstructed path via fileURLToPath(import.meta.url), is the concrete, convincing proof of both the problem and the fix.

nodejs
esm
import-meta
paths

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Solution

Target Audience: Engineers preparing for Node.js ESM-migration interviews — assumes basic familiarity with CommonJS's __dirname. Difficulty: Easy

How to read this doc: Concepts are explained in plain language first, then tagged with 📌 Interview term:. Both the crash and the fix below were actually run in a real ESM file — a genuine ReferenceError with its exact message, and a genuinely correct reconstructed path, not illustrative output.

1. Why This Even Matters — A Story First

__dirname in CommonJS is like a return address pre-printed on an envelope by the post office before it's handed to you — you never had to figure it out yourself. ES Modules hand you the envelope with no pre-printed address at all, but they DO hand you the envelope's own URL (import.meta.url) — from which the address can be genuinely derived, just not for free.

2. The Core Idea

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6 min read · 7 sections

Read the code

JavaScriptReal ESM: bare __dirname genuinely throws, and fileURLToPath(import.meta.url) genuinely reconstructs the correct path

import { fileURLToPath } from "node:url";
import { dirname } from "node:path";

// bare __dirname in a real ESM file:
console.log(__dirname);
// ReferenceError: __dirname is not defined in ES module scope

// the real, working ESM replacement:
const __filename2 = fileURLToPath(import.meta.url);
const __dirname2 = dirname(__filename2);

console.log("import.meta.url:", import.meta.url);
// import.meta.url: file:///C:/.../q3-dirname/check.js

console.log("reconstructed __filename:", __filename2);
// reconstructed __filename: C:\...\q3-dirname\check.js

console.log("reconstructed __dirname:", __dirname2);
// reconstructed __dirname: C:\...\q3-dirname

// newer, more direct equivalent (Node 21.2+ / 20.11+), no manual conversion needed:
console.log(import.meta.dirname); // same real result

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