Async script execution in Selenium Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this async JavaScript execution in Selenium?

Consider the following Selenium Java code snippet that executes an asynchronous JavaScript script. What will be the value of result after execution?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
Object result = js.executeAsyncScript(
  "var callback = arguments[arguments.length - 1];" +
  "setTimeout(function() { callback('done'); }, 1000);"
);

A "undefined"

B "done"

C null

D TimeoutException

💡 Hint

Remember that executeAsyncScript waits for the callback to be called before returning.

The async script uses setTimeout to call the callback with 'done' after 1 second. Selenium waits for this callback and returns its argument as the result.

❓ assertion

intermediate

Which assertion correctly verifies async script execution result?

You executed an async script that returns the string "success". Which assertion correctly verifies this in a JUnit test?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
Object result = js.executeAsyncScript(
  "var callback = arguments[arguments.length - 1];" +
  "callback('success');"
);

A assertEquals("success", result);

B assertTrue(result == "success");

C assertSame("success", result);

D assertNotNull(result);

💡 Hint

Use the assertion that compares values for equality.

assertEquals compares the expected and actual values correctly. assertTrue with == compares references, which is unreliable for strings.

🔧 Debug

advanced

Why does this async script cause a TimeoutException?

This Selenium Java code throws a TimeoutException. Identify the cause.

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
Object result = js.executeAsyncScript(
  "var callback = arguments[arguments.length - 1];" +
  "setTimeout(function() { console.log('done'); }, 5000);"
);

A The console.log causes the script to fail.

B The setTimeout delay is too long and causes a timeout error.

C The callback is never called, so Selenium times out waiting.

D executeAsyncScript does not support setTimeout.

💡 Hint

Check if the callback function is invoked in the script.

executeAsyncScript waits for the callback to be called. Here, callback is never called, so Selenium waits until timeout and throws TimeoutException.

❓ framework

advanced

How to set async script timeout in Selenium WebDriver Java?

Which code snippet correctly sets the async script timeout to 5 seconds?

A driver.setAsyncScriptTimeout(5);

B driver.manage().timeouts().pageLoadTimeout(5, TimeUnit.SECONDS);

C driver.manage().timeouts().implicitlyWait(5, TimeUnit.SECONDS);

D driver.manage().timeouts().setScriptTimeout(Duration.ofSeconds(5));

💡 Hint

Use the timeouts() method with setScriptTimeout and Duration.

setScriptTimeout sets the timeout for async scripts. The other options set different timeouts or are invalid.

🧠 Conceptual

expert

What happens if async script callback is called multiple times?

In Selenium Java, if an async script calls the callback function more than once, what is the behavior?

A Selenium returns the value from the first callback call and ignores subsequent calls.

B Selenium throws an exception on the second callback call.

C Selenium waits for all callback calls and returns the last value.

D Selenium concatenates all callback values and returns them.

💡 Hint

Think about how promises or callbacks usually behave in async APIs.

Selenium treats the first callback call as the completion signal and ignores any further calls to the callback.