title: “Waits”
weight: 4
WebDriver can generally be said to have a blocking API.
Because it is an out-of-process library that
instructs the browser what to do,
and because the web platform has an intrinsically asynchronous nature,
WebDriver does not track the active, real-time state of the DOM.
This comes with some challenges that we will discuss here.
From experience,
most intermittent issues that arise from use of Selenium and WebDriver
are connected to race conditions that occur between
the browser and the user’s instructions.
An example could be that the user instructs the browser to navigate to a page,
then gets a no such element error
when trying to find an element.
Consider the following document:
<!doctype html>
<meta charset=utf-8>
<title>Race Condition Example</title>
<script>
var initialised = false;
window.addEventListener("load", function() {
var newElement = document.createElement("p");
newElement.textContent = "Hello from JavaScript!";
document.body.appendChild(newElement);
initialised = true;
});
</script>
The WebDriver instructions might look innocent enough:
{{< code-tab >}}
{{< code-panel language=“java” >}}
driver.get(“file:///race_condition.html”);
WebElement element = driver.findElement(By.tagName(“p”));
assertEquals(element.getText(), “Hello from JavaScript!”);
{{< / code-panel >}}
{{< code-panel language=“python” >}}
driver.navigate(“file:///race_condition.html”)
el = driver.find_element(By.TAG_NAME, “p”)
assert el.text == “Hello from JavaScript!”
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
driver.Navigate().GoToUrl(“file:///race_condition.html”);
IWebElement element = driver.FindElement(By.TagName(“p”));
assertEquals(element.Text, “Hello from JavaScript!”);
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
require ‘selenium-webdriver’
driver = Selenium::WebDriver.for :firefox
begin
Navigate to URL
driver.get ‘file:///race_condition.html’
Get and store Paragraph Text
search_form = driver.find_element(:css,‘p’).text
“Hello from JavaScript!”.eql? search_form
ensure
driver.quit
end
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
await driver.get(‘file:///race_condition.html’);
const element = driver.findElement(By.css(‘p’));
assert.strictEqual(await element.getText(), ‘Hello from JavaScript!’);
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
driver.get(“file:///race_condition.html”)
val element = driver.findElement(By.tagName(“p”))
assert(element.text == “Hello from JavaScript!”)
{{< / code-panel >}}
{{< / code-tab >}}
The issue here is that the default
[page load strategy]({{< ref “/documentation/webdriver/drivers/options/” >}})
used in WebDriver listens for the document.readyState
to change to "complete" before returning from the call to navigate.
Because the p element is
added after the document has completed loading,
this WebDriver script might be intermittent.
It “might” be intermittent because no guarantees can be made
about elements or events that trigger asynchronously
without explicitly waiting—or blocking—on those events.
Fortunately, the normal instruction set available on
the [WebElement]({{< ref “/documentation/webdriver/elements/” >}}) interface—such
as WebElement.click and WebElement.sendKeys—are
guaranteed to be synchronous,
in that the function calls will not return
(or the callback will not trigger in callback-style languages)
until the command has been completed in the browser.
The advanced user interaction APIs,
[Keyboard]({{< ref “https://www.selenium.dev/documentation/en/webdriver/keyboard” >}})
and [Mouse]({{< ref “/documentation/webdriver/actions_api/mouse/” >}}),
are exceptions as they are explicitly intended as
“do what I say” asynchronous commands.
Waiting is having the automated task execution
elapse a certain amount of time before continuing with the next step.
To overcome the problem of race conditions
between the browser and your WebDriver script,
most Selenium clients ship with a wait package.
When employing a wait,
you are using what is commonly referred to
as an explicit wait.
Explicit wait
Explicit waits are available to Selenium clients
for imperative, procedural languages.
They allow your code to halt program execution,
or freeze the thread,
until the condition you pass it resolves.
The condition is called with a certain frequency
until the timeout of the wait is elapsed.
This means that for as long as the condition returns a falsy value,
it will keep trying and waiting.
Since explicit waits allow you to wait for a condition to occur,
they make a good fit for synchronising the state between the browser and its DOM,
and your WebDriver script.
To remedy our buggy instruction set from earlier,
we could employ a wait to have the findElement call
wait until the dynamically added element from the script
has been added to the DOM:
{{< code-tab >}}
{{< code-panel language=“java” >}}
WebDriver driver = new ChromeDriver();
driver.get(“https://google.com/ncr”);
driver.findElement(By.name(“q”)).sendKeys(“cheese” + Keys.ENTER);
// Initialize and wait till element(link) became clickable - timeout in 10 seconds
WebElement firstResult = new WebDriverWait(driver, Duration.ofSeconds(10))
.until(ExpectedConditions.elementToBeClickable(By.xpath(“//a/h3”)));
// Print the first result
System.out.println(firstResult.getText());
{{< / code-panel >}}
{{< code-panel language=“python” >}}
from selenium.webdriver.support.ui import WebDriverWait
def document_initialised(driver):
return driver.execute_script(“return initialised”)
driver.navigate(“file:///race_condition.html”)
WebDriverWait(driver).until(document_initialised)
el = driver.find_element(By.TAG_NAME, “p”)
assert el.text == “Hello from JavaScript!”
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
driver = new ChromeDriver();
driver.Url = “https://www.google.com/ncr”;
driver.FindElement(By.Name(“q”)).SendKeys(“cheese” + Keys.Enter);
WebDriverWait wait = new WebDriverWait(driver, TimeSpan.FromSeconds(10));
IWebElement firstResult = wait.Until(e => e.FindElement(By.XPath(“//a/h3”)));
Console.WriteLine(firstResult.Text);
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
require ‘selenium-webdriver’
driver = Selenium::WebDriver.for :firefox
wait = Selenium::WebDriver::Wait.new(:timeout => 10)
def document_initialised(driver)
driver.execute_script(‘return initialised’)
end
begin
driver.get ‘file:///race_condition.html’
wait.until{document_initialised driver}
search_form = driver.find_element(:css,‘p’).text
“Hello from JavaScript!”.eql? search_form
ensure
driver.quit
end
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
const documentInitialised = () =>
driver.executeScript(‘return initialised’);
await driver.get(‘file:///race_condition.html’);
await driver.wait(() => documentInitialised(), 10000);
const element = driver.findElement(By.css(‘p’));
assert.strictEqual(await element.getText(), ‘Hello from JavaScript!’);
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
driver.get(“https://google.com/ncr”)
driver.findElement(By.name(“q”)).sendKeys(“cheese” + Keys.ENTER)
// Initialize and wait till element(link) became clickable - timeout in 10 seconds
val firstResult = WebDriverWait(driver, Duration.ofSeconds(10))
.until(ExpectedConditions.elementToBeClickable(By.xpath(“//a/h3”)))
// Print the first result
println(firstResult.text)
{{< / code-panel >}}
{{< / code-tab >}}
We pass in the condition as a function reference
that the wait will run repeatedly until its return value is truthy.
A “truthful” return value is anything that evaluates to boolean true
in the language at hand, such as a string, number, a boolean,
an object (including a WebElement),
or a populated (non-empty) sequence or list.
That means an empty list evaluates to false.
When the condition is truthful and the blocking wait is aborted,
the return value from the condition becomes the return value of the wait.
With this knowledge,
and because the wait utility ignores no such element errors by default,
we can refactor our instructions to be more concise:
{{< code-tab >}}
{{< code-panel language=“java” >}}
WebElement foo = new WebDriverWait(driver, Duration.ofSeconds(3))
.until(driver → driver.findElement(By.name(“q”)));
assertEquals(foo.getText(), “Hello from JavaScript!”);
{{< / code-panel >}}
{{< code-panel language=“python” >}}
from selenium.webdriver.support.ui import WebDriverWait
driver.navigate(“file:///race_condition.html”)
el = WebDriverWait(driver).until(lambda d: d.find_element_by_tag_name(“p”))
assert el.text == “Hello from JavaScript!”
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
using (var driver = new FirefoxDriver())
{
var foo = new WebDriverWait(driver, TimeSpan.FromSeconds(3))
.Until(drv => drv.FindElement(By.Name(“q”)));
Debug.Assert(foo.Text.Equals(“Hello from JavaScript!”));
}
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
driver.get ‘file:///race_condition.html’
wait = Selenium::WebDriver::Wait.new(:timeout => 10)
ele = wait.until { driver.find_element(css: ‘p’)}
foo = ele.text
assert_match foo, ‘Hello from JavaScript’
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
let ele = await driver.wait(until.elementLocated(By.css(‘p’)),10000);
let foo = await ele.getText();
assert(foo == “Hello from JavaScript”);
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
driver.get(“file:///race_condition.html”)
val ele = WebDriverWait(driver, Duration.ofSeconds(10))
.until(ExpectedConditions.presenceOfElementLocated(By.tagName(“p”)))
assert(ele.text == “Hello from JavaScript!”)
{{< / code-panel >}}
{{< / code-tab >}}
In that example, we pass in an anonymous function
(but we could also define it explicitly as we did earlier so it may be reused).
The first and only argument that is passed to our condition
is always a reference to our driver object, WebDriver
(called d in the example).
In a multi-threaded environment, you should be careful
to operate on the driver reference passed in to the condition
rather than the reference to the driver in the outer scope.
Because the wait will swallow no such element errors
that are raised when the element is not found,
the condition will retry until the element is found.
Then it will take the return value, a WebElement,
and pass it back through to our script.
If the condition fails,
e.g. a truthful return value from the condition is never reached,
the wait will throw/raise an error/exception called a timeout error.
Options
The wait condition can be customised to match your needs.
Sometimes it is unnecessary to wait the full extent of the default timeout,
as the penalty for not hitting a successful condition can be expensive.
The wait lets you pass in an argument to override the timeout:
{{< code-tab >}}
{{< code-panel language=“java” >}}
new WebDriverWait(driver, Duration.ofSeconds(3)).until(ExpectedConditions.elementToBeClickable(By.xpath(“//a/h3”)));
{{< / code-panel >}}
{{< code-panel language=“python” >}}
WebDriverWait(driver, timeout=3).until(some_condition)
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
new WebDriverWait(driver, TimeSpan.FromSeconds(3)).Until(ExpectedConditions.ElementToBeClickable(By.XPath(“//a/h3”)));
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
wait = Selenium::WebDriver::Wait.new(:timeout => 10)
wait.until { driver.find_element(:id, ‘message’).displayed? }
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
await driver.wait(until.elementLocated(By.id(‘foo’)), 30000);
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
WebDriverWait(driver, Duration.ofSeconds(3)).until(ExpectedConditions.elementToBeClickable(By.xpath(“//a/h3”)))
{{< / code-panel >}}
{{< / code-tab >}}
Expected conditions
Because it is quite a common occurrence
to have to synchronise the DOM and your instructions,
most clients also come with a set of predefined expected conditions.
As might be obvious by the name,
they are conditions that are predefined for frequent wait operations.
The conditions available in the different language bindings vary,
but this is a non-exhaustive list of a few:
- alert is present
- element exists
- element is visible
- title contains
- title is
- element staleness
- visible text
You can refer to the API documentation for each client binding
to find an exhaustive list of expected conditions:
- Java’s org.openqa.selenium.support.ui.ExpectedConditions class
- Python’s selenium.webdriver.support.expected_conditions class
- .NET’s OpenQA.Selenium.Support.UI.ExpectedConditions type
Implicit wait
There is a second type of wait that is distinct from
explicit wait called implicit wait.
By implicitly waiting, WebDriver polls the DOM
for a certain duration when trying to find any element.
This can be useful when certain elements on the webpage
are not available immediately and need some time to load.
Implicit waiting for elements to appear is disabled by default
and will need to be manually enabled on a per-session basis.
Mixing explicit waits and implicit waits
will cause unintended consequences, namely waits sleeping for the maximum
time even if the element is available or condition is true.
Warning:
Do not mix implicit and explicit waits.
Doing so can cause unpredictable wait times.
For example, setting an implicit wait of 10 seconds
and an explicit wait of 15 seconds
could cause a timeout to occur after 20 seconds.
An implicit wait is to tell WebDriver to poll the DOM
for a certain amount of time when trying to find an element or elements
if they are not immediately available.
The default setting is 0, meaning disabled.
Once set, the implicit wait is set for the life of the session.
{{< code-tab >}}
{{< code-panel language=“java” >}}
WebDriver driver = new FirefoxDriver();
driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS);
driver.get(“http://somedomain/url_that_delays_loading”);
WebElement myDynamicElement = driver.findElement(By.id(“myDynamicElement”));
{{< / code-panel >}}
{{< code-panel language=“python” >}}
driver = Firefox()
driver.implicitly_wait(10)
driver.get(“http://somedomain/url_that_delays_loading”)
my_dynamic_element = driver.find_element(By.ID, “myDynamicElement”)
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
IWebDriver driver = new ChromeDriver();
driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(10);
driver.Url = “http://somedomain/url_that_delays_loading”;
IWebElement dynamicElement = driver.FindElement(By.Name(“dynamicElement”));
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
require ‘selenium-webdriver’
driver = Selenium::WebDriver.for :firefox
driver.manage.timeouts.implicit_wait = 10
begin
driver.get ‘http://somedomain/url_that_delays_loading’
search_form = driver.find_element(:id,‘dynamic_element’)
ensure
driver.quit
end
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
(async function(){
// Apply timeout for 10 seconds
await driver.manage().setTimeouts( { implicit: 10000 } );
// Navigate to url
await driver.get(‘http://somedomain/url_that_delays_loading’);
let webElement = driver.findElement(By.id(“myDynamicElement”));
}());
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
val driver = FirefoxDriver()
driver.manage().timeouts().implicitlyWait(10, TimeUnit.SECONDS)
driver.get(“http://somedomain/url_that_delays_loading”)
val myDynamicElement = driver.findElement(By.id(“myDynamicElement”))
{{< / code-panel >}}
{{< / code-tab >}}
FluentWait
FluentWait instance defines the maximum amount of time to wait for a condition,
as well as the frequency with which to check the condition.
Users may configure the wait to ignore specific types of exceptions whilst waiting,
such as NoSuchElementException when searching for an element on the page.
{{< code-tab >}}
{{< code-panel language=“java” >}}
// Waiting 30 seconds for an element to be present on the page, checking
// for its presence once every 5 seconds.
Wait wait = new FluentWait(driver)
.withTimeout(Duration.ofSeconds(30))
.pollingEvery(Duration.ofSeconds(5))
.ignoring(NoSuchElementException.class);
WebElement foo = wait.until(new Function<WebDriver, WebElement>() {
public WebElement apply(WebDriver driver) {
return driver.findElement(By.id(“foo”));
}
});
{{< / code-panel >}}
{{< code-panel language=“python” >}}
driver = Firefox()
driver.get(“http://somedomain/url_that_delays_loading”)
wait = WebDriverWait(driver, 10, poll_frequency=1, ignored_exceptions=[ElementNotVisibleException, ElementNotSelectableException])
element = wait.until(EC.element_to_be_clickable((By.XPATH, “//div”)))
{{< / code-panel >}}
{{< code-panel language=“csharp” >}}
using (var driver = new FirefoxDriver())
{
WebDriverWait wait = new WebDriverWait(driver, timeout: TimeSpan.FromSeconds(30))
{
PollingInterval = TimeSpan.FromSeconds(5),
};
wait.IgnoreExceptionTypes(typeof(NoSuchElementException));
var foo = wait.Until(drv => drv.FindElement(By.Id(“foo”)));
}
{{< / code-panel >}}
{{< code-panel language=“ruby” >}}
require ‘selenium-webdriver’
driver = Selenium::WebDriver.for :firefox
exception = Selenium::WebDriver::Error::NoSuchElementError
begin
driver.get ‘http://somedomain/url_that_delays_loading’
wait = Selenium::WebDriver::Wait.new(timeout: 30, interval: 5, message: ‘Timed out after 30 sec’, ignore: exception)
foo = wait.until { driver.find_element(id: ‘foo’)}
ensure
driver.quit
end
{{< / code-panel >}}
{{< code-panel language=“javascript” >}}
const {Builder, until} = require(‘selenium-webdriver’);
(async function example() {
let driver = await new Builder().forBrowser(‘firefox’).build();
await driver.get(‘http://somedomain/url_that_delays_loading’);
// Waiting 30 seconds for an element to be present on the page, checking
// for its presence once every 5 seconds.
let foo = await driver.wait(until.elementLocated(By.id(‘foo’)), 30000, ‘Timed out after 30 seconds’, 5000);
})();
{{< / code-panel >}}
{{< code-panel language=“kotlin” >}}
val wait = FluentWait(driver)
.withTimeout(Duration.ofSeconds(30))
.pollingEvery(Duration.ofSeconds(3))
.ignoring(NoSuchElementException::class.java)
val foo = wait.until {it.findElement(By.id(“foo”)) }
{{< / code-panel >}}
{{< / code-tab >}}