[解決済み] JavaScriptまたはjQueryを使用してMac OS XまたはWindowsコンピュータを検出する最良の方法

var is_OSX = /(Mac|iPhone|iPod|iPad)/i.test(navigator.platform);
var is_iOS = /(iPhone|iPod|iPad)/i.test(navigator.platform);

var is_Mac = navigator.platform.toUpperCase().indexOf('MAC') >= 0;
var is_iPhone = navigator.platform == "iPhone";
var is_iPod = navigator.platform == "iPod";
var is_iPad = navigator.platform == "iPad";

/* Output */
var out = document.getElementById('out');
if (!is_OSX) out.innerHTML += "This NOT a Mac or an iOS Device!";
if (is_Mac) out.innerHTML += "This is a Mac Computer!\n";
if (is_iOS) out.innerHTML += "You're using an iOS Device!\n";
if (is_iPhone) out.innerHTML += "This is an iPhone!";
if (is_iPod) out.innerHTML += "This is an iPod Touch!";
if (is_iPad) out.innerHTML += "This is an iPad!";
out.innerHTML += "\nPlatform: " + navigator.platform;

<pre id="out"></pre>

setTimeout(test, 1000); //delay for demonstration

function test() {

  var mac = /(Mac|iPhone|iPod|iPad)/i.test(navigator.platform);

  if (mac) {
    document.getElementById('close').classList.add("left");
  }
}

#window {
  position: absolute;
  margin: 1em;
  width: 300px;
  padding: 10px;
  border: 1px solid gray;
  background-color: #DDD;
  text-align: center;
  box-shadow: 0px 1px 3px #000;
}
#close {
  position: absolute;
  top: 0px;
  right: 0px;
  width: 22px;
  height: 22px;
  margin: -12px;
  box-shadow: 0px 1px 3px #000;
  background-color: #000;
  border: 2px solid #FFF;
  border-radius: 22px;
  color: #FFF;
  text-align: center;
  font: 14px"Comic Sans MS", Monaco;
}
#close.left{
  left: 0px;
}

<div id="window">
  <div id="close">x</div>
  <p>Hello!</p>
  <p>If the "close button" change to the left side</p>
  <p>you're on a Mac like system!</p>
</div>