Javascript 硒“；NoSuchAlertError:无警报打开“；错误

在Selenium中，我单击一个按钮，出现一个警报框，我试图接受警报框，但它给了我一个错误

          element.click();
          driver.switchTo().alert().accept();

这很不一致。。。有时测试通过，有时它给我错误

错误如下所示：

NoSuchAlertError: no alert open
  (Session info: chrome=34.0.1847.131)
  (Driver info: chromedriver=2.9.248307,platform=Mac OS X 10.9.2 x86_64)
      at new bot.Error (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/atoms/error.js:109:18)
      at Object.bot.response.checkResponse (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/atoms/response.js:106:9)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/webdriver.js:276:20
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1465:10
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:678:49
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/http/http.js:96:5
      at IncomingMessage.<anonymous> (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/http/index.js:114:7)
      at IncomingMessage.EventEmitter.emit (events.js:117:20)
      at _stream_readable.js:920:16
      at process._tickCallback (node.js:415:13)
  ==== async task ====
  WebDriver.switchTo().alert()
      at webdriver.WebDriver.schedule (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/webdriver.js:267:15)
      at webdriver.WebDriver.TargetLocator.alert (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/webdriver.js:1429:27)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/test/bandbooking/form.js:87:39
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at then (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:478:7)
      at Object.webdriver.promise.asap (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:723:11)
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1609:25)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at then (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:478:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:369:18)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at then (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:478:7)
      at Object.webdriver.promise.asap (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:723:11)
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1609:25)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at then (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:478:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:369:18)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1465:10
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at then (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:478:7)
      at Object.webdriver.promise.asap (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:723:11)
      at newFrame.then.e (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1614:25)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at webdriver.promise.ControlFlow.resolveFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1519:9)
      at webdriver.promise.ControlFlow.getNextTask_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1488:12)
      at webdriver.promise.ControlFlow.runEventLoop_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1446:59)
      at wrapper [as _onTimeout] (timers.js:252:14)
      at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
  ==== async task ====
      at Context.<anonymous> (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/testing/index.js:126:14)
      at Test.Runnable.run (/usr/local/lib/node_modules/mocha/lib/runnable.js:196:15)
      at Runner.runTest (/usr/local/lib/node_modules/mocha/lib/runner.js:374:10)
      at /usr/local/lib/node_modules/mocha/lib/runner.js:452:12
      at next (/usr/local/lib/node_modules/mocha/lib/runner.js:299:14)
      at /usr/local/lib/node_modules/mocha/lib/runner.js:309:7
      at next (/usr/local/lib/node_modules/mocha/lib/runner.js:247:23)
      at /usr/local/lib/node_modules/mocha/lib/runner.js:271:7
      at done (/usr/local/lib/node_modules/mocha/lib/runnable.js:185:5)
      at /usr/local/lib/node_modules/mocha/lib/runnable.js:199:9
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/testing/index.js:92:5
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1465:10
      at Object.webdriver.promise.asap (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:732:5)
      at newFrame.then.e (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1614:25)
      at /Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/goog/base.js:1178:15
      at webdriver.promise.ControlFlow.runInNewFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1598:20)
      at notify (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:428:12)
      at notifyAll (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:397:7)
      at resolve (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:375:7)
      at fulfill (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:493:5)
      at webdriver.promise.ControlFlow.resolveFrame_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1519:9)
      at webdriver.promise.ControlFlow.getNextTask_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1488:12)
      at webdriver.promise.ControlFlow.runEventLoop_ (/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/promise.js:1446:59)
      at wrapper [as _onTimeout] (timers.js:252:14)
      at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)

NoSuchAlertError:未打开警报
（会话信息：chrome=34.0.1847.131）
（驱动程序信息：chromedriver=2.9.248307，平台=Mac OS X 10.9.2 x86_64）
在新的bot.Error（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/atoms/Error.js:109:18）
在Object.bot.response.checkResponse（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/atoms/response.js:106:9）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/webdriver.js:276:20
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
在notifyAll（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:397:7）
解析时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:375:7）
完成时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:493:5）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1465:10
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
在notifyAll（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:397:7）
解析时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:375:7）
完成时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:493:5）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
在notifyAll（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:397:7）
解析时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:375:7）
完成时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:493:5）
位于/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:678:49
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/http/http.js:96:5
在收到消息时。（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/http/index.js:114:7）
在IncomingMessage.EventEmitter.emit（events.js:117:20）
at_stream_readable.js:920:16
在进程中调用（node.js:415:13）
==异步任务====
WebDriver.switchTo（）.alert（）
在webdriver.webdriver.schedule（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumdriver/lib/webdriver/webdriver.js:267:15）
位于webdriver.webdriver.TargetLocator.alert（/Users/kstrife/Desktop/experiments/seleniumNode/selenium-webdriver/lib/webdriver/webdriver.js:1429:27）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/test/bandbooking/form.js:87:39
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
在notifyAll（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:397:7）
解析时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:375:7）
完成时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:493:5）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
在notifyAll（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:397:7）
解析时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:375:7）
完成时（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:493:5）
at/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/goog/base.js:1178:15
位于webdriver.promise.ControlFlow.runInNewFrame（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:1598:20）
在notify（/Users/kstrife/Desktop/experiments/seleniumNode/seleniumwebdriver/lib/webdriver/promise.js:428:12）
当时（/Users/k）
element.click();
driver.sleep(1000);
driver.switchTo().alert().accept();

element.click();
while (true)
{
    try
    {
        driver.switchTo().alert().accept();
        break;
    }
    catch (NoSuchAlertError error)
    {
        Thread.sleep(100);
    }
}

int count = 0;
do{
   if (driver.getWindowHandles().size() > 1) {
     // Alert is present
     driver.switchTo().alert().accept();
     break;
   }
} while(count < 100);

WebDriverWait wait = new WebDriverWait(driver, 10);
WebElement element = wait.until(ExpectedConditions.alertIsPresent());

driver.switchTo().alert().accept();

// this is the documented solution, which doesn't work
driver.switchTo().alert().dismiss().then(null, function(e) {
  if (e.code !== webdriver.ErrorCode.NO_SUCH_ALERT) {
    throw e;
  }
});

driver.switchTo().alert().thenCatch(function (e) {
    // 27 maps to bot.ErrorCode.NO_MODAL_DIALOG_OPEN: http://selenium.googlecode.com/git/docs/api/javascript/source/lib/atoms/error.js.src.html#l31
    if (e.code !== 27) { throw e; }
})
.then(function (alert) {
    if (alert) { return alert.dismiss(); }
});