Executing JavaScript in Selenium Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JavaScript execution in Selenium?

Consider the following Selenium Java code snippet that executes JavaScript to get the page title. What will be the value of pageTitle after execution?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
String pageTitle = (String) js.executeScript("return document.title;");

A "" (empty string)

B The current page's title as a String

C null

D Throws a ClassCastException

💡 Hint

Remember that executeScript returns an Object that you can cast to the expected type.

The JavaScript executed returns the document's title as a string. Selenium's executeScript returns an Object, which can be cast to String safely here.

❓ assertion

intermediate

Which assertion correctly verifies JavaScript execution result?

You execute JavaScript to get the number of links on a page. Which assertion correctly checks that the number is 10?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
Long linkCount = (Long) js.executeScript("return document.getElementsByTagName('a').length;");

A assertEquals(10, linkCount);

B assertTrue(linkCount == 10);

C assertEquals(10L, linkCount);

D assertEquals("10", linkCount);

💡 Hint

Check the type returned by executeScript for numeric values.

executeScript returns a Long for numeric JavaScript values. So comparing with 10L (long literal) is correct.

🔧 Debug

advanced

Why does this JavaScript execution throw an exception?

This Selenium Java code throws a ClassCastException. What is the cause?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
String result = (String) js.executeScript("return 5 + 5;");

A executeScript returns a Long for numeric results, not a String

B The JavaScript syntax is invalid

C Casting to String is always safe here

D executeScript cannot return primitive values

💡 Hint

Check the Java type returned for JavaScript numeric results.

JavaScript numeric results are returned as Long in Java, so casting to String causes ClassCastException.

🧠 Conceptual

advanced

What is the best way to scroll to an element using JavaScript in Selenium?

You want to scroll the page so a specific WebElement is visible. Which JavaScript snippet executed via Selenium is best?

Selenium Java

JavascriptExecutor js = (JavascriptExecutor) driver;
WebElement element = driver.findElement(By.id("myElement"));

A js.executeScript("element.scrollIntoView();");

B js.executeScript("window.scrollTo(0, 1000);");

C js.executeScript("document.body.scrollTop = 1000;");

D js.executeScript("arguments[0].scrollIntoView();", element);

💡 Hint

Use arguments to pass WebElement safely to JavaScript.

Passing the element as an argument and calling scrollIntoView on it is the correct and reliable way.

❓ framework

expert

How to safely execute asynchronous JavaScript and get result in Selenium Java?

You want to execute asynchronous JavaScript that calls a callback when done. Which Selenium method and approach is correct?

A Use executeAsyncScript and call arguments[arguments.length - 1]() in JS when done

B Use executeScript and wait manually for result

C Use executeScript and return a Promise from JS

D Use executeAsyncScript but do not call the callback in JS

💡 Hint

Asynchronous JS requires a callback to signal completion.

executeAsyncScript waits until the JS calls the last argument as a callback to return the result.