How can one get the file path of the caller function in node.js?

You need to fiddle with the inner workings of v8. See: the wiki entry about the JavaScript Stack Trace API.

I’ve based a little test on some code in a proposed commit and it seems to work. You end up with an absolute path.

// omfg.js

module.exports = omfg

function omfg() {
  var caller = getCaller()
  console.log(caller.filename)
}

// private

function getCaller() {
  var stack = getStack()

  // Remove superfluous function calls on stack
  stack.shift() // getCaller --> getStack
  stack.shift() // omfg --> getCaller

  // Return caller's caller
  return stack[1].receiver
}

function getStack() {
  // Save original Error.prepareStackTrace
  var origPrepareStackTrace = Error.prepareStackTrace

  // Override with function that just returns `stack`
  Error.prepareStackTrace = function (_, stack) {
    return stack
  }

  // Create a new `Error`, which automatically gets `stack`
  var err = new Error()

  // Evaluate `err.stack`, which calls our new `Error.prepareStackTrace`
  var stack = err.stack

  // Restore original `Error.prepareStackTrace`
  Error.prepareStackTrace = origPrepareStackTrace

  // Remove superfluous function call on stack
  stack.shift() // getStack --> Error

  return stack
}

And a test that includes omfg module:

#!/usr/bin/env node
// test.js

var omfg = require("./omfg")

omfg()

And you will get on the console the absolute path of test.js.

---

EXPLANATION

This is not so much a “node.js” issue as it is a “v8” issue.

See: Stack Trace Collection for Custom Exceptions

Error.captureStackTrace(error, constructorOpt) adds to the error parameter a stack property, which evaluates by default to a String (by way of FormatStackTrace). If Error.prepareStackTrace(error, structuredStackTrace) is a Function, then it is called instead of FormatStackTrace.

So, we can override Error.prepareStackTrace with our own function that will return whatever we want–in this case, just the structuredStackTrace parameter.

Then, structuredStackTrace[1].receiver is an object representing the caller.