XF 2.1 Using mustache in HTML widget


As I read in previous discussions, mustache.js is built into XenForo.
I found the correct syntax and implemented it (with no errors!),
but for some reason it does not render the data I want:
I have a JS file (as a template) with a JSON that contains the data I need.
All works fine on codePen and locally on my computer but no data is sent to the widget.

When writing the script directly into the widget code- into script tags- other widgets get affected too, and do not display the data they are supposed to display.

Any idea what I am doing wrong?