Internet Explorer 11 error?

Hi,

Internet Explorer is logging a JS error related to the ecs.js file in the plugin.

function ECS_do_action(name, ...params){
  if(ECS_hooks[name]) 
     ECS_hooks[name].forEach(func => func(...params));
}

The error can be seen on any page of the website. Site URL is https://www.aheadstudy.org but is behind basic authentication right now (I can provide credentials separately if needed). Has this issue come up before? It may not be ECS as there are other JS errors, but this is the first one that appears.

Thank you,
Ben