Nodejs export is not a function

I have the following in a module file:

module.exports = {
    myfunc: myfunc
};

var myfunc = function(callback){    
        callback(err,reply);    
};

In an other file I got the reference to that module

var mymodule = require('./modules/mymodule');
mymodule.myfunc(function(err, reply){ ... });

When I call the mymodule.myfunc() I get an error saying "property 'myfunc' is not a function". This happens only with exported functions. The same module exports some 'string' fields and these are working just fine.

asked Jan 13, 2014 at 13:49

When you assign module.exports, the myfunc function is still undefined. Try to assign it after declaring it:

var myfunc = function(callback){    
    callback(err,reply);    
};

module.exports = {
    myfunc: myfunc
};

answered Jan 13, 2014 at 14:04

AiorosAioros

4,3231 gold badge16 silver badges20 bronze badges

3

To preserve your original ordering of module.exports at the top of your file, change your var myfunc initialization to a function myfunc declaration so that the latter is hoisted.

module.exports = {
    myfunc: myfunc
};

function myfunc(callback){    
    callback(err,reply);    
};

Declarations are hoisted, but initializations are not, which is why your original example did not work. w3schools has a practical description of JavaScript Hoisting.

answered Apr 16, 2017 at 15:18

Ken LinKen Lin

1,61720 silver badges17 bronze badges

1

All we need is an easy explanation of the problem, so here it is.

I’m trying to use badPort function inside another function (getPort) in module.exports like so:

DEFAULT_PORT = 80;

module.exports = {
        badPort:
                (c_port, min=80, max=90) => {
                        return isNaN(c_port) || !between(c_port, min, max);
                },
        getPort:
                (c_port, min=80, max=90) => {
                        console.log(this.badPort(c_port));
                        return this.badPort(c_port) ? 80 : c_port;
                },
};     

However, when I use this.badPort(c_port) it throws an exception:

TypeError: this.badPort is not a function

But it’s clearly a function as initialised right above it.

If however I take out the (), this.badPort always returns undefined.

Why is this happening and how would I be able to correctly use the function inside module.exports? Is it possible to also declare the "Global variable" DEFAULT_PORT in module.exports this way?

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

You can do it, by changing this to module.exports:

DEFAULT_PORT = 80;

module.exports = {
        badPort:
                (c_port, min=80, max=90) => {
                        return isNaN(c_port) || !between(c_port, min, max);
                },
        getPort:
                (c_port, min=80, max=90) => {
                        console.log(module.exports.badPort(c_port));
                        return module.exports.badPort(c_port) ? 80 : c_port;
                },
};

And about second question… you would have to redefine your module, to use that variable externally, like this:

module.exports.DEFAULT_PORT = 80;

Then you will have access to it:

var mod = require('mymodule');
console.log(mod.DEFAULT_PORT);

I am not aware of any other way.

Method 2

Have you try this to change ":" by "=" like:

DEFAULT_PORT = 80;

module.exports = {
    badPort = (c_port, min=80, max=90) => {
                    return isNaN(c_port) || !between(c_port, min, max);
            },
    getPort = (c_port, min=80, max=90) => {
                    console.log(this.badPort(c_port));
                    return this.badPort(c_port) ? 80 : c_port;
            },
};  

Method 3

To reference badPort from the other function you can write it this way:

DEFAULT_PORT = 80;

const badPort = (c_port, min=80, max=90) => {
  return isNaN(c_port) || !between(c_port, min, max);
};

const getPort = (c_port, min=80, max=90) => {
  console.log(badPort(c_port));

  return badPort(c_port) ? 80 : c_port;
};

module.exports = {
  badPort,
  getPort
};     

And if you’re curious on how to import it correctly, here is an example of a correct import from another js file in the same directory:

const port = require('./port.js');
console.log(port.badPort(1000));

And your default port can be an environment variable using process.env https://nodejs.org/dist/latest-v8.x/docs/api/process.html

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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