WebDriver Bidi APIs

In Selenium 4, new Evented APIs were introduced that allow users to be able to capture events from the browser as they happen rather than using the traditional approach of Request/Response that WebDriver has used for other APIs.

Internally WebDriver will create a WebSocket connection to the browser for events and commands to be transmitted.

The following list of APIs will be growing as the Selenium project works through supporting real world use cases. If there is a missing API, please raise a feature request.

Mutation Observation

Mutation Observation is the ability to capture events via WebDriver BiDi when there are DOM mutations on a specific element in the DOM.

WebDriver driver = new FirefoxDriver();

HasLogEvents logger = (HasLogEvents) driver;

AtomicReference<DomMutationEvent> seen = new AtomicReference<>();
CountDownLatch latch = new CountDownLatch(1);
logger.onLogEvent(domMutation(mutation -> {

WebElement span = driver.findElement(By.cssSelector("span"));

((JavascriptExecutor) driver).executeScript("arguments[0].setAttribute('cheese', 'gouda');", span);

assertThat(latch.await(10, SECONDS)).isTrue();


from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.wait import WebDriverWait

driver = webdriver.Chrome()
async with driver.log.mutation_events() as event:
    driver.find_element(By.ID, "reveal").click()
    WebDriverWait(driver, 5)\
        .until(EC.visibility_of(driver.find_element(By.ID, "revealed")))

assert event["attribute_name"] == "style"
assert event["current_value"] == ""
assert event["old_value"] == "display:none;"


IWebDriver driver = new FirefoxDriver();
driver.Url = "http://www.google.com";
// Please help with a .NET example

require 'selenium-webdriver'
driver = Selenium::WebDriver.for :firefox
  driver.on_log_event(:mutation) { |mutation| mutations.push(mutation) }
  driver.navigate.to url_for('dynamic.html')
  driver.find_element(id: 'reveal').click
  wait.until { mutations.any? }
  mutation = mutations.first
  expect(mutation.element).to eq(driver.find_element(id: 'revealed'))
  expect(mutation.attribute_name).to eq('style')
  expect(mutation.current_value).to eq('')
  expect(mutation.old_value).to eq('display:none;')

let {Builder, By} = require('selenium-webdriver');
driver = new Builder().forBrowser('firefox').build();

(async function test(){

    const cdpConnection = await driver.createCDPConnection('page')
    await driver.logMutationEvents(cdpConnection, function (event) {
        assert.strictEqual(event['attribute_name'], 'style')
        assert.strictEqual(event['current_value'], '')
        assert.strictEqual(event['old_value'], 'display:none;')

    await driver.get("https://www.google.com")

    let element = driver.findElement({ id: 'reveal' })
    await element.click()
    let revealed = driver.findElement({ id: 'revealed' })
    await driver.wait(until.elementIsVisible(revealed), 5000)


val driver = FirefoxDriver()
// Please help us create an example for Kotlin