function-location

locateV8() returns the absolute source file path for a function or class at runtime.

Install

npm install function-location

Supports Node.js 20 through 26 on Linux x64 (glibc), Windows x64, and macOS (x64 and arm64).

Usage

import { locateV8 } from 'function-location';

class ExampleClass {}
function exampleFunction() {}

locateV8(ExampleClass);     // /path/to/file.ts
locateV8(exampleFunction);  // /path/to/file.ts

API

locateV8(input: Function): string | undefined

• Works for classes, functions, methods, arrow functions, and async/generator functions, named or anonymous.
• Bound functions resolve to the location of their target function.
• Functions compiled with vm resolve to the script filename.
• Returns undefined when no source file exists: builtins (Math.max, Array), functions created by eval or new Function, and proxies.
• Throws TypeError: Function argument expected when input is not a function.

Performance sample

This library uses a synchronous native addon lookup instead of the inspector protocol.

Sample comparison against an inspector-protocol baseline:

Approach	Median time / call	Relative speed
locateV8	0.0254 µs	14438.93x faster
inspector protocol	367.4543 µs	baseline

Results vary by environment; treat them as sample measurements only. Methodology and raw samples: docs/BENCHMARK.md

Links

• Contributing / support matrix
• MIT License