I'm trying to detect if the user is using Windows 11 in order to serve the correct binaries when they click a download button. I've found Microsoft's suggestion for how to do this here. They suggest using the navigator.userAgentData.getHighEntropyValues function which returns a promise containing the platform version. Here is the code they suggest:

navigator.userAgentData.getHighEntropyValues(["platformVersion"])
 .then(ua => {
   if (navigator.userAgentData.platform === "Windows") {
     const majorPlatformVersion = parseInt(ua.platformVersion.split('.')[0]);
     if (majorPlatformVersion >= 13) {
       console.log("Windows 11 or later");
      }
      else if (majorPlatformVersion > 0) {
        console.log("Windows 10");
      }
      else {
        console.log("Before Windows 10");
      }
   }
   else {
     console.log("Not running on Windows");
   }
 });

My problem is that this function is asynchronous and returns a promise instead of returning the value. I don't want to have to convert all of the code I use to parse user agents for every platform in to an async function.

At first, I thought I would use await instead of using the promise like this:

let ua = await navigator.userAgentData.getHighEntropyValues(["platformVersion"])

However, this meant that I would need to make the function that contains it async. And since this same code needs to work on older browsers that don't support async and ones that do, I can't do that.

Is there a way to detect if the user is using Windows 11 without this API? Or using this API but in a way that doesn't require async?