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.

Practice

1. What is the main purpose of using JavascriptExecutor in Selenium Java?

easy

A. To locate elements on the page using JavaScript selectors

B. To execute JavaScript code directly in the browser during a test

C. To start the Selenium WebDriver session

D. To generate test reports automatically

Solution

1. Step 1: Understand the role of JavascriptExecutor

   JavascriptExecutor allows running JavaScript code inside the browser from Selenium tests.

2. Step 2: Identify the main use case

   It is mainly used to perform actions or retrieve information that Selenium WebDriver cannot do directly.

3. Final Answer:

   To execute JavaScript code directly in the browser during a test -> Option B

4. Quick Check:

   JavascriptExecutor runs JS code in browser [OK]

Hint: Remember: JavascriptExecutor runs JS code inside browser [OK]

Common Mistakes:

• Confusing JavascriptExecutor with element locators
• Thinking it starts WebDriver sessions
• Assuming it generates reports

2. Which of the following is the correct way to cast a WebDriver instance to JavascriptExecutor in Selenium Java?

easy

A. JavascriptExecutor js = driver.executeScript();

B. JavascriptExecutor js = driver.getJavascriptExecutor();

C. JavascriptExecutor js = new JavascriptExecutor(driver);

D. JavascriptExecutor js = (JavascriptExecutor) driver;

Solution

1. Step 1: Recall the casting syntax in Java

   To use JavascriptExecutor, you cast the WebDriver instance like this: (JavascriptExecutor) driver.

2. Step 2: Check each option

   JavascriptExecutor js = (JavascriptExecutor) driver; uses correct casting syntax. The other options are invalid method calls or constructors.

3. Final Answer:

   JavascriptExecutor js = (JavascriptExecutor) driver; -> Option D

4. Quick Check:

   Cast driver to JavascriptExecutor using (JavascriptExecutor) [OK]

Hint: Casting uses (JavascriptExecutor) before driver [OK]

Common Mistakes:

• Using non-existent methods like getJavascriptExecutor()
• Trying to instantiate JavascriptExecutor with new keyword
• Calling executeScript() without casting

3. What will be the output of the following code snippet?

JavascriptExecutor js = (JavascriptExecutor) driver;
String title = (String) js.executeScript("return document.title;");
System.out.println(title);

medium

A. Prints the current page's title

B. Throws a ClassCastException

C. Prints 'undefined'

D. Prints the URL of the page

Solution

1. Step 1: Understand the JavaScript executed

   The script returns document.title, which is the page's title as a string.

2. Step 2: Check the casting and output

   The returned object is cast to String and printed, so it outputs the page title.

3. Final Answer:

   Prints the current page's title -> Option A

4. Quick Check:

   executeScript returns document.title string [OK]

Hint: executeScript returns JS value; cast to String for title [OK]

Common Mistakes:

• Expecting URL instead of title
• Not casting return value to String
• Confusing output with undefined or errors

4. Identify the error in the following code snippet:

JavascriptExecutor js = (JavascriptExecutor) driver;
js.executeScript("arguments[0].click();");

medium

A. Incorrect casting of driver to JavascriptExecutor

B. executeScript method does not exist

C. Missing WebElement argument to click()

D. JavaScript syntax error in the string

Solution

1. Step 1: Analyze the executeScript call

   The script uses arguments[0].click(); which requires a WebElement passed as an argument.

2. Step 2: Check the method call parameters

   No WebElement is passed to executeScript, so it will fail at runtime.

3. Final Answer:

   Missing WebElement argument to click() -> Option C

4. Quick Check:

   arguments[0] needs a WebElement passed [OK]

Hint: Pass WebElement as argument when using arguments[0] [OK]

Common Mistakes:

• Forgetting to pass WebElement argument
• Assuming casting is wrong
• Thinking executeScript method is missing

5. You want to scroll a page to a specific WebElement using JavaScript in Selenium Java. Which code snippet correctly achieves this?

hard

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

B. js.executeScript("window.scrollTo(element);");

C. js.executeScript("scrollToElement(arguments[0]);", element);

D. js.executeScript("document.scrollTo(arguments[0]);");

Solution

1. Step 1: Recall JavaScript method to scroll to element

   The correct JS method is scrollIntoView(true) called on the element.

2. Step 2: Check the Selenium executeScript usage

   Pass the WebElement as an argument and use arguments[0].scrollIntoView(true); to scroll.

3. Final Answer:

   js.executeScript("arguments[0].scrollIntoView(true);", element); -> Option A

4. Quick Check:

   Use scrollIntoView with element argument [OK]

Hint: Use arguments[0].scrollIntoView(true) with element [OK]

Common Mistakes:

• Using window.scrollTo with element (invalid)
• Calling non-existent scrollToElement function
• Not passing element as argument