How to get current state of expanded/collapsed groups?

Question

I'm unable to capture current state of a tree data grid which includes capturing the expanded & collapsed groups.

I am trying to capture the expanded groups in slickgrid so as to retain their expanded state after I have refreshed the grid. I am trying to capture the grouping keys of all groups that have been expanded but I have been unable to do so.

this.gridDataViewObj.onGroupExpanded.subscribe(result => {
  console.log(result);
});