D3v4 Tree works, but fails in latest d3, why?

Hi,

I have two code bases setup

  1. A D3v4 Repo with a working Tree view. Note by clicking on the black plus marks the tree opens, and the white minus marks make it close, This all works perfectly on D3v4
  2. A d3v6 Repo with exactl the same stixtree.js file (copy and paste over). Yet this time, clicking on the boxes withe the plus signs does not open the graph.`

Why does the same code work in D3v4, but not on D3v7? Can you help please?