JS Use a class method at google chart setOnLoadCallback

I had a working JS code to display some google chart on page. I thought I refactor this into a JS class like this (cleared and minimized the code for the sample):

class MyChar {
   show(title) {
      this.title = title;
      google.charts.load('current', { 'packages': ['bar'] });

    _googleChartOnLoadCallback() {
        console.log("_googleChartOnLoadCallback is called", this.title);
       // do stuff needed here

I want to call this like this:

var myChart = new MyChart();
myChart.show("My cool chart");

I expected to see on the developer console the title, but got an error pointing to the 1st line of the _googleChartOnLoadCallback method:

Uncaught (in promise) TypeError: this is undefined

The google chart loader is (of the html head):

<script type="text/javascript" src="https://www.gstatic.com/charts/loader.js"></script>

My question is: can or cannot use a class method on a callback – or am I missing something? If I cannot use a callback – then how to insert (add) chart specific data to the callback func?

Thanks in advance!


Found a solution:

var f = this._googleChartOnLoadCallback.bind(this);