Edge/IE fails to load Apple's JavaScript

We noticed that the JavaScript pulled in as described in "Configuring Your Webpage for Sign In with Apple" uses nonstandard syntax (namely, spread operator for object literals). This is unsupported on Edge and IE browsers. (Compatability chart: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax). We haven't been able to find any mention of the issue in Apple's documentation or developer forum. Is this a known issue that Apple will address? Or are Edge and Internet Explorer browsers not supported for sign-in with apple?