Question: I am developing a node.js app, and I want to use a module I am creating for the node.js server also on the client side. 

An example module would be circle.js:

```
var PI = Math.PI;

exports.area = function (r) {
  return PI * r * r;
};

exports.circumference = function (r) {
  return 2 * PI * r;
};

```

and you do a simple 

```
var circle = require('./circle')

```

to use it in node.

How could I use that same file in the web directory for my client side javascript?

Answer: 
This seems to be how to make a module something you can use on the client side.

<https://caolan.org/posts/writing_for_node_and_the_browser.html>

mymodule.js:

```
(function(exports){

    // your code goes here

   exports.test = function(){
        return 'hello world'
    };

})(typeof exports === 'undefined'? this['mymodule']={}: exports);

```

And then to use the module on the client:

```
<script src="mymodule.js"></script>
<script>
    alert(mymodule.test());
</script>

```

This code would work in node:

```
var mymodule = require('./mymodule');

```
[Webmake](https://github.com/medikoo/modules-webmake) was made to port CommonJS/NodeJS modules to browser. Give it a try