示例：判断是否是苹果设备

   const isIos = /ipad|iPhone|Mac/i.test(window.navigator.userAgent)

一、只读属性 window.navigator

二、检测浏览器并返回浏览器名称字符串

var sBrowser, sUsrAg = navigator.userAgent;

// The order matters here, and this may report false positives for unlisted browsers.

if (sUsrAg.indexOf("Firefox") > -1) {
  sBrowser = "Mozilla Firefox";
} else if (sUsrAg.indexOf("Opera") > -1 || sUsrAg.indexOf("OPR") > -1) {
  sBrowser = "Opera";
} else if (sUsrAg.indexOf("Trident") > -1) {
  sBrowser = "Microsoft Internet Explorer";
} else if (sUsrAg.indexOf("Edge") > -1) {
  sBrowser = "Microsoft Edge";
} else if (sUsrAg.indexOf("Chrome") > -1) {
  sBrowser = "Google Chrome or Chromium";
} else if (sUsrAg.indexOf("Safari") > -1) {
  sBrowser = "Apple Safari";
} else {
  sBrowser = "unknown";
}

alert("当前浏览器为: " + sBrowser);

三、MDN官方链接

https://developer.mozilla.org/zh-CN/docs/Web/API/Window/navigator