How to use the RuntimeApi in HTML5 Apps?

Wendigo

Hi Community,
I'm developing an HTML5 game and would like to access the file system for storing my save games. (Unfortunately I can't use the localStorage since the reboots caused by the memory bug on the Fairphone2 sometimes erase the stored data)
In the docs I found an article about the RuntimeApi which contains a function called "getApplicationWritableLocation". So I assume that it is possible to access the filesystem via JavaScript from within the HTML5 App. I have never accessed the Ubuntu Touch specific API before and the documentation is scarce. So I'm a little lost.

String getApplicationWritableLocation() Retrieves the fileystem location where the application is allowed to write its data in.

https://api-docs.ubports.com/sdk/apps/html5/RuntimeApi/RuntimeApi.html

My questions:

How do I access the API in the first place. Do I need to require/import something or can I just access the "external" object?
This is the example from the doc page above:

var api = external.getUnityObject('1.0');
    api.RuntimeApi.getApplication(function(application) {
      console.log('Application name: ' + application.getApplicationName());
    });

Where can I find information about the actual function that can read/write to the path retrieved by "ApplicationWritableLocation"?

Many thanks in advance

Edit:
After a little research I found this old site from Ubuntu that references Apache Cordova which indeed has a File API:
https://docs.ubuntu.com/phone/en/apps/html-5/api
But unfortunately they dropped Ubuntu support last year.
Looks like I really need to use the functionality from the RuntimeApi from Ubuntu Touch (if there is one at all).

L-00081

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