Modify HTML with Javascript in a webview

[M V]

I've got some HTML loaded in a webview inside a tasker scene which I want to be modified when a particular element is clicked. I wrote some javascript that handles this fine while in a browser but I haven't been able to use it inside tasker. How would I go about doing that?

This is the javascript that I have

document.getElementById('icon').onclick = function() {
  var x = document.getElementById('material');
  x.classList.toggle("active");
}