Detect private browsing mode in mobile Safari on iOS5

gistfile1.js

var testKey = 'qeTest', storage = window.sessionStorage;

try {

	// Try and catch quota exceeded errors
	storage.setItem(testKey, '1');
	storage.removeItem(testKey);
} catch (error) {
	if (error.code === DOMException.QUOTA_EXCEEDED_ERR && storage.length === 0)
		alert('Hello, private browser.');
	else throw error;
}