How to detect iPad Pro as iPad using javascript?

iPadPro reports navigator.platform the browser as 'MacIntel', but that is the same as other platforms.

Currently (2019) difference between iPadPro and the other platforms is that iPadPro is touch enabled.

Here are a couple of helpful methods.

function isIOS() {
  if (/iPad|iPhone|iPod/.test(navigator.platform)) {
    return true;
  } else {
    return navigator.maxTouchPoints &&
      navigator.maxTouchPoints > 2 &&
      /MacIntel/.test(navigator.platform);
  }
}

function isIpadOS() {
  return navigator.maxTouchPoints &&
    navigator.maxTouchPoints > 2 &&
    /MacIntel/.test(navigator.platform);
}

I guess that iPad Pro is upgraded to iPadOS 13 Beta. Since Apple claimed Desktop-Class Browsing with Safari on iPadOS, it seems mobile Safari also mimics macOS behavior and user agent.

So, the short answer is it's not possible.

However you can try workarounds from answers to this question.