private-mode-detection.js

function retry(isDone, next) {
  var current_trial = 0, max_retry = 50, interval = 10, is_timeout = false;
  var id = window.setInterval(
    function() {
      if (isDone()) {
        window.clearInterval(id);
        next(is_timeout);
      }
      if (current_trial++ > max_retry) {
        window.clearInterval(id);
        is_timeout = true;
        next(is_timeout);
      }
    },
    10
  );
}

function isIE10OrLater(user_agent) {
  var ua = user_agent.toLowerCase();
  if (ua.indexOf('msie') === 0 && ua.indexOf('trident') === 0) {
    return false;
  }
  var match = /(?:msie|rv:)\s?([\d\.]+)/.exec(ua);
  if (match && parseInt(match[1], 10) >= 10) {
    return true;
  }
  // MS Edge Detection from this gist: https://gist.github.com/cou929/7973956
  var edge = /edge/.exec(ua); 
  if (edge && edge[0] == "edge") { 
    return true; 
  }
  return false;
}

function detectPrivateMode(callback){
  var is_private;

  if (window.webkitRequestFileSystem) {
    window.webkitRequestFileSystem(
      window.TEMPORARY, 1,
      function() {
        is_private = false;
      },
      function(e) {
        console.log(e);
        is_private = true;
      }
    );
  } else if (window.indexedDB && /Firefox/.test(window.navigator.userAgent)) {
    var db;
    try {
      db = window.indexedDB.open('test');
    } catch(e) {
      is_private = true;
    }

    if (typeof is_private === 'undefined') {
      retry(
        function isDone() {
          return db.readyState === 'done' ? true : false;
        },
        function next(is_timeout) {
          if (!is_timeout) {
            is_private = db.result ? false : true;
          }
        }
      );
    }
  } else if (isIE10OrLater(window.navigator.userAgent)) {
    is_private = false;
    try {
      if (!window.indexedDB) {
        is_private = true;
      }                 
    } catch (e) {
      is_private = true;
    }
  } else if (window.localStorage && /Safari/.test(window.navigator.userAgent)) {
    // One-off check for weird sports 2.0 polyfill
    // This also impacts iOS Firefox and Chrome (newer versions), apparently
    // @see bglobe-js/containers/App.js:116
    if (window.safariIncognito) {
      is_private = true;
    } else {
      try {
        window.openDatabase(null, null, null, null);
      } catch (e) {
        is_private = true;
      }

      try {
        window.localStorage.setItem('test', 1);
      } catch(e) {
        is_private = true;
      }
    } 

    if (typeof is_private === 'undefined') {
      is_private = false;
      window.localStorage.removeItem('test');
    }
  }  

  retry(
    function isDone() {
      return typeof is_private !== 'undefined' ? true : false;
    },
    function next(is_timeout) {
      callback(is_private);
    }
  );
}

detectPrivateMode(function(itIs){
    if(itIs){
      document.body.style.backgroundColor = 'red';
    }else{
      document.body.style.backgroundColor = 'green';
    }
});