# Module format

Caplin Trader 4 uses the [CommonJS](https://en.wikipedia.org/wiki/CommonJS) module format, while retaining support for Caplin Trader 3’s module format, [NamespacedJS](http://bladerunnerjs.org/docs/reference/namespaced_style_code/).

Modules written in CommonJS format and modules written in NamespacedJS format are fully interoperable in Caplin Trader 4 and can reference, extend and inherit from each other.

To take advantage of advances in JavaScript tooling, the next major release of Caplin Trader following Caplin Trader 4 will drop support for NamespacedJS modules.

## A comparison of NamespacedJS and CommonJS formats

This section compares two functionally-equivalent source files for an example module, `Bar`. One source file is written in NamespacedJS format and the other source file is written in CommonJS format.

### CommonJS module format

The `Bar` module is defined in a file named `abc/def/Bar.js`. The only object revealed by the module is the object assigned to `module.exports`. The externally-defined class, `Foo`, is referenced by its fully qualified name in the invocation of `require`; thereafter, the class is referenced by a local variable.

To learn more about module format in BladeRunnerJS, see [Modules](http://bladerunnerjs.org/docs/concepts/modules/) on the [BladeRunnerJS](http://bladerunnerjs.org/) website.

```js
var Foo = require('abc/def/Foo');

function Bar() { 
     this.foo = new Foo(); 
     this.foo.doFoo();
     this.doBar();
} 

Bar.prototype.doBar = function(){
    alert("Doing bar!");
}

module.exports = Bar;
```

### NamespacedJS module format

The `Bar` module is defined in a file named `abc/def/Bar.js`. Variables that are declared with a namespace prefix are accessible from outside of the module. The externally-defined class, `Foo`, must be fully qualified in order for BladeRunnerJS’s class loader to correctly locate the file in which the class is defined: `abc/def/Foo.js`.

```js
abc.def.Bar = function() { 
    this.foo = new abc.def.Foo(); 
    this.foo.doFoo();
    this.doBar();
}

abc.def.Bar.prototype.doBar = function() {
    alert("Doing bar!");
};
```

## Migration path from NamespacedJS to CommonJS format

Caplin Trader 4 supports modules of both formats: NamespacedJS and CommonJS. The next major release of Caplin Trader will drop support for NamespacedJS.

In order to maintain a clean upgrade path from Caplin Trader 4 to future releases of Caplin Trader, it is recommended that you migrate your NamespacedJS modules to CommonJS format.

### Migrating your modules to CommonJS

Caplin provide a command-line tool to automate the majority of the work in converting NamespacedJS code to CommonJS formatted modules. The tool supports stepped migration: one blade, bladeset, or library at a time. For instructions and to download the tool, see the [caplin/gc-cli](https://github.com/caplin/gc-cli) page on GitHub. Please raise any issues with the tool by posting to the [caplin/gc-cli](https://github.com/caplin/gc-cli) repository or by contacting the Caplin support team.

For information on CommonJS compliance in Caplin Trader, see [BladeRunnerJS Wiki: CommonJS compliance](https://github.com/BladeRunnerJS/brjs/wiki/BladeRunnerJS-CommonJs-Compliance).

### Using existing NamespacedJS modules with Caplin Trader 4

By default, Caplin Trader 4’s build tool, BladeRunnerJS, assumes that a module’s directory hierarchy contains JavaScript files in CommonJS module format.

To indicate to BladeRunnerJS that a module’s directory hierarchy contains NamespacedJS-formatted code, in the root of the directory hierarchy, create a file called `.js-style` containing the text 'namespaced-js'. To create the file `.js-style` in one step from the Linux command line, execute the following command from the root of the module’s directory hierarchy:

```
echo namespaced-js > .js-style
```

For more information on using NamespacedJS modules within Caplin Trader 4, see [Namespaced-style code](http://bladerunnerjs.org/docs/reference/namespaced_style_code/) on the BladeRunnerJS website.

## Modules in Caplin Trader 4.4

Caplin Trader 4.4 is the first version of Caplin Trader 4 to be released with all SDK modules in CommonJS format. This changes some aspects of the bundling process and may have implications for your code. For more information, see the [CT 4.4 Upgrade Guide](../ct-44-upgrade-guide.md).

---

**See also:**

* [BladeRunnerJS Wiki: CommonJS compliance](https://github.com/BladeRunnerJS/brjs/wiki/BladeRunnerJS-CommonJs-Compliance)
* [BladeRunnerJS.org: Modules](http://bladerunnerjs.org/docs/concepts/modules/)
* [BladeRunnerJS.org: Namespaced style code](http://bladerunnerjs.org/docs/reference/namespaced_style_code/)
* [BladeRunnerJS.org: Classes](http://bladerunnerjs.org/docs/concepts/classes/)
* [BladeRunnerJS.org: Interfaces](http://bladerunnerjs.org/docs/concepts/interfaces/)
* [BladeRunnerJS.org: Libraries](http://bladerunnerjs.org/docs/concepts/libraries/)
* [BladeRunnerJS.org: Assets](http://bladerunnerjs.org/docs/concepts/assets/)