Question

75

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

rated 0 times [ 77] [ 2] / answers: 1 / hits: 37895 / 12 Years ago, mon, november 5, 2012, 12:00:00

Here is some sample code from three files:

// foo.js

var myFunc = require(./myFunc);

function foo(){

   myFunc(message);

}



// bar.js

var myFunc = require(./myFunc);

function bar(){

   myFunc(message);

}



// myFunc.js

module.exports = myFunc;

function myFunc(arg1){

   console.log(arg1);

   // Here I need the file path of the caller function

   // For example, /path/to/foo.js and /path/to/bar.js

}

I need to get the file path of the caller function dynamically, without any extra argument passing, for myFunc.

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adilene

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3 Years ago

answered 12 Years ago mustafaericho · Accepted Answer

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.