# Third-party library manifest file rules

This topic explains what Third-party Library Manifests (_library.manifest_ files) are, why you might need to use them, and the rules for doing so. For details of adding third-party code libraries to your _BladeRunner_ application, see [How Can I Add Third-party Libraries to an App?](add-third-party-libraries.md)

Third-party _library.manifest_ files allow you to specify JavaScript and CSS files that will be loaded for a third-party library, and also let you specify dependencies between different third-party libraries. Any image files referred to by the third-party CSS will be loaded implicitly.

Manifest files are processed by the _JavaScript bundler_ and the _CSS bundler_, but they are not compulsory; if a _library.manifest_ is not present in the folder of a particular third party library, the _bundlers_ will revert to the default behaviour described under [Rules](#rules), below.

## Manifest File Format

A third-party library manifest is essentially a _Java .properties_ file with the name "_library.manifest_". It contains the following keys:

| Key | Value |
| --- | --- |
| depends | If the library described by this manifest is dependent on any other third-party libraries, they should be listed under this key. Each listed name should correspond to the folder name of that library, as it exists within the `thirdparty-libraries/` directory. Multiple dependencies should be separated by commas. |
| js | This key specifies the JavaScript files that will be included by the JavaScript bundler for this library. If there is more than one JS file, they should be separated by commas. |
| css | This key specifies the CSS files which will be included for this library by the CSS Bundler. If there is more than one, they should be comma-separated. |

**For example:**

![br_3pl_rules_1](../../../images/br_3pl_rules_1.png)

### Contents of a sample library.manifest file

```
depends: amcharts
js: library-file-1.js, library-file-2.js
css: style.css
```

In the above example, the _library.manifest_ file is stating that it has a dependency on _amcharts_ (and its _library.manifest_ contents).

Now, when this library is referenced, it will load _amcharts_ as a dependency.

### Rules

1. Each third-party library can (but does not have to) have one _library.manifest_ file, which is stored in the root folder for that library’s resource files.
2. If "**depends**" is absent from the manifest, the library is considered to have no dependencies.
3. If "**js**" is absent from the manifest, only the first .js file in the library directory will be included by the _JavaScript Bundler_.
4. If "**css**" is absent, no CSS files will be included for the library.

   **📌 NOTE**\
   At time of writing, a known issue means that all CSS files present in the library directory will be included, whether in the manifest or not, but this won’t be the case for long, and if you want to include CSS within a library, it is better to declare it in the manifest.
5. If any of these keys has multiple values, the order in which they are listed determines the include order in which the corresponding library files will be loaded.
6. If a library does _not_ have a _library.manifest_ file, the library will be handled by the default behaviour. This means that the rules for all three keywords being absent will be applied. I.e: 
   1. No dependencies will be assumed.
   2. Only the first _.js_ file in the library folder will be included by the bundlers.
   3. No CSS will be included by the bundlers.