I got an error that is "UnhandledPromiseRejectionWarning: NoSuchSessionError: no such session"

Question

Premise · What I want to realize

I'm trying to automate testing with Selenium × Node.js, but it got blocked at the investigation stage...

testing environment

• Mac OS10.12.6
• Node 8.11.1
• Selenium Server 3.12.0
• Selenium WebDriver 4.0.0
• ChromeDriver 2.38

What I did

1. Installation of Node.js

From official site

2. Installation of selenium-webdriver

Install via npm

$ npm install selenium-webdriver

3. Installation of selenium-server

Install via Homebrew

$ brew install selenium-server-standalone

4. Install of ChromeDriver

ChromeDriver - WebDriver for Chrome

→ Move the file after downloading the driver

$ mv /Users/username/Downloads/chromedriver ./
$ ls -la
total 31920 
drwxr-xr-x 7 username staff 238 5 24 17:42 . 
drwxr-xr-x+ 55 username staff 1870 5 24 17:42 .. 
-rwxr-xr-x@ 1 username staff 11917200 4 20 16:39 chromedriver 
drwxr-xr-x 41 username staff 1394 5 24 16:45 node_modules 
-rw-r--r-- 1 username staff 9367 5 24 16:45 package-lock.json

5. Start-up the Selenium Server

$ selenium-server -port 4444 & [1] 33415 C02SY1XFGTFJ:selenium username$ 18:04:14.512 INFO [GridLauncherV3.launch] - Selenium build info: version: '3.11.0', revision: 'e59cfb3' 18:04:14.513 INFO [GridLauncherV3$1.launch] - Launching a standalone Selenium Server on port 4444 2018-05-24 18:04:14.624:INFO::main: Logging initialized @441ms to org.seleniumhq.jetty9.util.log.StdErrLog 18:04:14.882 INFO [SeleniumServer.boot] - Welcome to Selenium for Workgroups.... 18:04:14.882 INFO [SeleniumServer.boot] - Selenium Server is up and running on port 4444

Problems occurring · Error messages

Write a test code as a sample

$ vim sample.js

// Initialization of WebDriver
const webdriver = require('selenium-webdriver');
// Browser selection
const browser = new webdriver.Builder().forBrowser('chrome').build();

// Get page title
browser.get('http://example.selenium.jp/reserveApp/').then(()=>{
    browser.getTitle().then(title => console.log('Page title:',title))
});

// Exit the browser
browser.close();
browser.quit();

When you execute the above code, ...

$ node sample.js 
(node:13216) UnhandledPromiseRejectionWarning: NoSuchSessionError: no such session
  (Driver info: chromedriver=2.38.552518 (183d19265345f54ce39cbb94cf81ba5f15905011),platform=Mac OS X 10.12.6 x86_64)
    at Object.checkLegacyResponse (/Users/ko-kamenashi/selenium/node_modules/selenium-webdriver/lib/error.js:585:15)
    at parseHttpResponse (/Users/ko-kamenashi/selenium/node_modules/selenium-webdriver/lib/http.js:533:13)
at Executor.execute (/Users/ko-kamenashi/selenium/node_modules/selenium-webdriver/lib/http.js:468:26)
at <anonymous>
at process._tickCallback (internal/process/next_tick.js:188:7)
(node:13216) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:13216) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

I got the errors. What shoud I do? Could you lend me a hand? Thank you for your reading.

Answer 1

The error is here: const browser = new webdriver.Builder().forBrowser('chrome').build();

Best way: 
(async ()=> { 
await const browser = new webdriver.Builder().forBrowser('chrome').build();
)();