Is there a use for anonymous functions when writing a nodejs module. I understand that we use anonymous function to limit the scope of the variables/functions used to a specific module. However, in nodejs, we use modules.exports to made a function or variable available outside the module, hence shouldn't an anonymous function be unnecessary?

The reason I ask this is because popular node modules (like async.js) extensively use anonymous functions.

Example with anonymous function

1) test_module.js

(function(){

var test_module = {}; 
var a = "Hello";
var b = "World";

test_module.hello_world = function(){

    console.log(a + " " + b);

};

module.exports = test_module;


}());

2) test.js

var test_module = require("./test_module");

test_module.hello_world();


try {   
    console.log("var a is " + a + "in this scope");
}
catch (err){

    console.log(err);
}

try {   
    console.log("var a is " + b + "in this scope");
}
catch (err){

    console.log(err);
}

Output:

Hello World
[ReferenceError: a is not defined]
[ReferenceError: b is not defined]

Example without anonymous function

1) test_module2.js

var test_module = {}; 
var a = "Hello";
var b = "World";

test_module.hello_world = function(){

    console.log(a + " " + b);

};

module.exports = test_module;

2) test2.js

var test_module = require("./test_module2");

test_module.hello_world();


try {   
    console.log("var a is " + a + "in this scope");
}
catch (err){

    console.log(err);
}

try {   
    console.log("var a is " + b + "in this scope");
}
catch (err){

    console.log(err);
}

Output:

Hello World
[ReferenceError: a is not defined]
[ReferenceError: b is not defined]

Is there a use for anonymous functions when writing a nodejs module. I understand that we use anonymous function to limit the scope of the variables/functions used to a specific module. However, in nodejs, we use modules.exports to made a function or variable available outside the module, hence shouldn't an anonymous function be unnecessary?

The reason I ask this is because popular node modules (like async.js) extensively use anonymous functions.

Example with anonymous function

1) test_module.js

(function(){

var test_module = {}; 
var a = "Hello";
var b = "World";

test_module.hello_world = function(){

    console.log(a + " " + b);

};

module.exports = test_module;


}());

2) test.js

var test_module = require("./test_module");

test_module.hello_world();


try {   
    console.log("var a is " + a + "in this scope");
}
catch (err){

    console.log(err);
}

try {   
    console.log("var a is " + b + "in this scope");
}
catch (err){

    console.log(err);
}

Output:

Hello World
[ReferenceError: a is not defined]
[ReferenceError: b is not defined]

Example without anonymous function

1) test_module2.js

var test_module = {}; 
var a = "Hello";
var b = "World";

test_module.hello_world = function(){

    console.log(a + " " + b);

};

module.exports = test_module;

2) test2.js

var test_module = require("./test_module2");

test_module.hello_world();


try {   
    console.log("var a is " + a + "in this scope");
}
catch (err){

    console.log(err);
}

try {   
    console.log("var a is " + b + "in this scope");
}
catch (err){

    console.log(err);
}

Output:

Hello World
[ReferenceError: a is not defined]
[ReferenceError: b is not defined]

• javascript
• node.js

• 4 Node.js modules provide encapsulation them-selves. So there is no need to wrap assignment of module.exports this way. You might need it if you have nested classes. But that fact itself would actually hint to wrap this nested class into another module... – Kirill Slatin Commented Apr 7, 2015 at 13:11

1 Answer 1

You absolutely DO NOT need the anonymous function

Node guarantees you a clean "namespace" to work in with each file

The only things "visible" from each file/module are things that you explicitly export using module.exports

Your test_module2.js is much preferred though I would still make a couple changes. Most notably, you don't have to define myModule as an object in your file. You can think of the file as a module already.

test_module3.js

var a = "Hello";
var b = "World";

function helloWorld() {
  console.log(a, b);
}

exports.helloWorld = helloWorld;