XLS to JSON from file

I want to get some data from a .xls file into my app. Unfortunately I found almost nothing to manage that.
This: https://ciphertrick.com/2016/06/05/read-excel-files-convert-json-node-js/ was the only hint, but I don’t think, that is really compatible with ionic 2.
Can please anybody help me?

The workflow should look like this:

  1. Choose a file from the system (the above link works with a simpel form, so no specific native file chooser for ios/android is needed)
  2. The XLS should be converted to JSON and then stored.

https://github.com/SheetJS/js-xlsx/issues/525#issuecomment-285437898 Shows how to deal with XLS, but the file chooser part is not that clear to me.

Thanks in advance!