Locate module-relative resources
Build a path to a file shipped beside the current CommonJS module.
Node.js · Pipe
__filename
__filename is a CommonJS module variable containing the current module’s absolute file path, with symbolic links resolved. It is module-local, not a true global.
- Since
- v0.0.1
How it works
In a CommonJS module, __filename is a string containing the absolute path of the current module, with symbolic links resolved. Its value is local to each module rather than a true global, so dependencies see their own file paths.
Syntax
__filenameReturns
A string containing the current CommonJS module's resolved absolute file path.
Key points
- Node.js has provided
__filenamesince version 0.0.1. - It identifies the module containing the reference.
- The returned path is absolute and reflects symlink resolution.
- Use
__dirnamewhen the directory, rather than the full filename, is needed. - Node.js documents these CommonJS-specific variables as available within modules.
Common mistakes
- When the entry file is launched through a command, its resolved path can differ from the path text supplied to Node.js.
Example: Print module location
console.log(__filename);
console.log(__dirname);Run this CommonJS file with Node.js to print its absolute module path and containing directory.
When to use it
Identify the executing module
Log which source file produced a message or error.
Inspect dependency locations
Distinguish the paths of an application module and its dependencies.
Interview questions
QWhat does __filename contain?
__filename is a CommonJS-only module variable whose value is the current module's absolute path, with symlinks resolved. It is scoped to the module, so each dependency receives its own filename.
Follow-up: How would you obtain the equivalent in an ES module? Use the ES module URL context, such as import.meta.url, and convert it with the URL and path utilities when a filesystem path is needed.
QIs __filename a global variable?
It is not a genuine global. Node.js provides it in the scope of CommonJS modules, alongside variables such as __dirname, exports, module, and require().
Follow-up: Why does this distinction matter? A variable that is module-local cannot be assumed to exist in unrelated module scopes or in the same form under another module system.
QWhat happens when different CommonJS modules read __filename?
The value depends on the module where the expression appears. If module a loads dependency b, a sees the absolute path to a.js, while b sees the absolute path to b.js.
Follow-up: How can this help locate resources? Resolve a resource relative to the current module's directory rather than relying on the process's current working directory.
Related
__dirnameCommonJS modulesmodulerequire()