Begin with H5P

Hi everybody,
I would like to work with H5P, but I don't understand how to use xAPIEvent. Could you help me, please?
I work on Drupal 8 and Opigno 2. 

H5P.externalDispatcher.on('xAPI', function (event) {
  console.log(event.data.statement);
});

When I would use the last function, I have an error, on the statement .on whose is not define.
I get this function on the documentation page of H5P: https://h5p.org/documentation/x-api

Why do I want to use this?
I need to build a module that gets the score of H5P exercise. I find this function who is interesting for me.

H5P.externalDispatcher.on('xAPI', function(event){
  if (event.getScore() === event.getMaxScore() && event.getMaxScore() > 0){
    console.log('do something useful here');
  }
});

I think I have a problem with my initialization, I use the following code to init my H5P variable. 

var H5P = window.H5P = window.H5P || {};

Thank's