# Partially applying themes

**The main focus of Loki Theme Kit is to remove legacy JavaScript and replace it with better solutions. This works with any Luma-based theme. However, not all JavaScript is replaced yet. Here you will find a way to gradually cross-over.**

Because this project is not done yet, some pages (like the checkout with Loki Checkout and CMS pages) are very easy to migrate: You will want a new Loki theme to be applied to those pages. Yet other pages need more work and therefore require a fallback to a regular theme.

To allow for this, you can use the [Yireo_ThemeByRoute](https://github.com/yireo/Yireo_ThemeByRoute) module. It allows to define a JSON file `app/etc/theme-by-route.json` to determine under which routes (aka URLs) which theme should be loaded:

```json
{
  "Loki/luma": [
    "cms/index/index",
    "cms/page/view"
  ]
}
```

## Your own child theme
If you are working with a Luma-based theme, you simply keep it as is. By adding the `LokiTheme_LumaComponents` module, JavaScript will be replaced for the theme is configured in the DI XML type for `LokiTheme\LumaComponents\Config\ThemeConfig`. However, because the gradual migration, it is best to first create a new child theme of your own theme.

Assume that your own theme is called `YireoTraining/default`. First of all, let's create a new theme `YireoTraining/loki` that extends from it. Add a `registration.php` file and a `theme.xml` file. You don't need much more.

Now, let's apply this theme to the relevant pages by adding a file `app/etc/theme-by-route.json`:

```json
{
  "Loki/luma": [
    "cms/index/index",
    "checkout"
  ],
  "YireoTraining/loki": [
    "cms/index/index",
    "checkout"
  ]
}
```

What is left is checking which functionality remains. Where things fail, most likely due to missing JavaScript, new JavaScript needs to be added.