# Extension

An extension helper allows you to add/render additional libraries and/or append some javascript code just before/after
the generated one. To understand how it works, you will dig into a simple example.

First, you need to create your own extension:

``` php
namespace My\Own\Helper\Extension;

use Ivory\GoogleMap\Helper\Extension\ExtensionHelperInterface;
use Ivory\GoogleMap\Map;

class MyExtensionHelper implements ExtensionHelperInterface
{
    /**
     * {@inheritdoc}
     */
    public function renderLibraries(Map $map)
    {
        // Here, we can render additional libraries...
        return '<script type="text/javascript" src="//your/own/library.js"></script>'.PHP_EOL;
    }

    /**
     * {@inheritdoc}
     */
    public function renderBefore(Map $map)
    {
        // Here, we can render js code just before the generated one.
        return 'var before = \'before\''.PHP_EOL;
    }

    /**
     * {@inheritdoc}
     */
    public function renderAfter(Map $map)
    {
        // Here, we can render js code just after the generated one.
        return 'var after = \'after\''.PHP_EOL;
    }
}
```

Then, you need to register you extension on the map helper. To do that, you must define your extension as service:

``` yaml
services:
    my.own.extension_helper:
        class: My\Own\Helper\Extension\MyExtensionHelper
        public: false
```

When your service (extension) is well registered in the container, you just need to configure it:

``` yaml
ivory_google_map:
    extensions:
        my_extension: my.own.extension_helper
```

Enjoy!