How to use hotjar with ember ?

I need to use hotjar for work, but i have some difficulties to set it up. The project is an ember project, and i have found this project to integrate hotjar : https://github.com/byrnedo/ember-hotjar

In this github page, it says : "in routes and controller you will have _hj.push available", but i can't manage to make it work and i can't find any information about how to set it up.

I added this in config/environment.js :

hotjar: {
  id: my-id
},

And in a route, if i do this :

console.log(this.get('_hj'))

I get this result in the console :

ƒ () {
    (window.hj.q = window.hj.q || []).push(arguments);
  }

Meaning that hotjar is successfully installed, but when i'm trying to something like :

this.get('_hj').push('trigger', 'hello_world');

An error appears saying :

Uncaught TypeError: this.get(...).push is not a function

Does anyone know how to make it work or if i'm making something wrong ?