JavaScript executor basics in Selenium Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JavaScript executor call in Selenium?

Consider the following Python Selenium code snippet that uses JavaScript executor to get the page title. What will be printed?

Selenium Python

title = driver.execute_script('return document.title;')
print(title)

A Prints the entire HTML content of the page

B Prints None because execute_script returns nothing

C Raises a SyntaxError in Python

D Prints the current page title as a string

💡 Hint

Remember that execute_script can return values from JavaScript to Python.

The JavaScript code 'return document.title;' returns the page title string to Python, so the variable 'title' holds that string and prints it.

❓ assertion

intermediate

Which assertion correctly verifies the page background color using JavaScript executor?

You want to check if the page background color is exactly 'rgb(255, 255, 255)'. Which Python assertion with JavaScript executor is correct?

Selenium Python

color = driver.execute_script('return window.getComputedStyle(document.body).backgroundColor;')

A assert color != 'rgb(255, 255, 255)'

B assert color == 'rgb(255, 255, 255)'

C assert color = 'rgb(255, 255, 255)'

D assert color is 'rgb(255, 255, 255)'

💡 Hint

Use the equality operator '==' for value comparison in assertions.

Option B uses the correct equality operator '==' to compare the string values. Option B uses assignment '=' which is invalid in assert. Option B asserts the opposite. Option B uses 'is' which checks identity, not value equality.

❓ locator

advanced

Which JavaScript executor code correctly scrolls to an element by its ID?

You want to scroll the page to an element with id 'footer' using JavaScript executor in Selenium Python. Which code snippet is correct?

A driver.execute_script('document.getElementById("footer").scrollIntoView();')

B driver.execute_script('document.querySelector("#footer").scrollTo();')

C driver.execute_script('document.getElementById("footer").scrollToView();')

D driver.execute_script('document.querySelector("footer").scrollIntoView();')

💡 Hint

Use the correct JavaScript method to scroll an element into view.

Option A correctly uses getElementById and scrollIntoView(). Option A uses scrollTo() which is not a method of elements. Option A uses a non-existent method scrollToView(). Option A uses querySelector with 'footer' which selects elements by tag name, not id.

🔧 Debug

advanced

Why does this JavaScript executor call raise an error?

This Python Selenium code raises an error. Identify the cause.

Selenium Python

driver.execute_script('return document.querySelectorAll(".btn").forEach(el => el.click())')

A Python cannot execute JavaScript with arrow functions

B Syntax error in the JavaScript arrow function

C forEach returns undefined, so returning it causes an error

D document.querySelectorAll does not exist

💡 Hint

Check what the forEach method returns in JavaScript.

The forEach method returns undefined in JavaScript. Returning undefined from execute_script is allowed but if Python expects a value, it may cause issues. The error is likely due to returning undefined. The arrow function syntax is correct, and querySelectorAll exists. Python can execute any JavaScript string.

❓ framework

expert

In Selenium Python, which approach correctly waits for an element to be clickable before clicking it using JavaScript executor?

You want to wait until an element with id 'submit' is clickable, then click it using JavaScript executor. Which code snippet correctly implements this?

Selenium Python

from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

wait = WebDriverWait(driver, 10)

A

wait.until(EC.element_to_be_clickable((By.ID, 'submit')))
driver.execute_script('document.getElementById("submit").click();')

B

driver.execute_script('document.getElementById("submit").click();')
wait.until(EC.element_to_be_clickable((By.ID, 'submit')))

C

wait.until(EC.presence_of_element_located((By.ID, 'submit')))
driver.execute_script('document.getElementById("submit").click();')

D

wait.until(EC.visibility_of_element_located((By.ID, 'submit')))
driver.execute_script('document.getElementById("submit").click();')

💡 Hint

Wait for the element to be clickable before clicking it.

Option A waits for the element to be clickable, which means visible and enabled, then clicks it via JavaScript executor. Option A clicks before waiting, which may fail. Option A waits only for presence, not clickability. Option A waits for visibility but not necessarily enabled state.

Practice

1. What is the main purpose of using execute_script in Selenium with Python?

easy

A. To run JavaScript code inside the browser during a test

B. To start the Selenium WebDriver server

C. To locate elements using CSS selectors

D. To take screenshots of the browser window

Solution

1. Step 1: Understand the role of execute_script

   This method allows running JavaScript code inside the browser from Selenium tests.

2. Step 2: Compare with other Selenium functions

   Other functions locate elements or control the browser, but execute_script specifically runs JS code.

3. Final Answer:

   To run JavaScript code inside the browser during a test -> Option A

4. Quick Check:

   execute_script runs JS code [OK]

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

Common Mistakes:

• Confusing execute_script with element locating methods
• Thinking execute_script starts WebDriver server
• Assuming execute_script takes screenshots

2. Which of the following is the correct syntax to run JavaScript code that returns the page title using Selenium's execute_script in Python?

easy

A. driver.execute_script('return document.title')

B. driver.execute_script(document.title)

C. driver.execute_script('document.title')

D. driver.execute_script(return document.title)

Solution

1. Step 1: Check correct string usage for JS code

   The JavaScript code must be passed as a string, so quotes are needed around 'return document.title'.

2. Step 2: Verify the return keyword usage

   To get a value back from JS, 'return' must be used inside the string.

3. Final Answer:

   driver.execute_script('return document.title') -> Option A

4. Quick Check:

   JS code as string with return keyword [OK]

Hint: Always pass JS code as a quoted string with return [OK]

Common Mistakes:

• Passing JS code without quotes
• Omitting the return keyword when expecting a value
• Using invalid syntax without quotes or return

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

title = driver.execute_script('return document.title')
print(title)

medium

A. Prints the WebDriver object reference

B. Prints None because execute_script returns nothing

C. Prints the current page's title as a string

D. Raises a syntax error due to missing quotes

Solution

1. Step 1: Understand what execute_script returns

   When JavaScript code returns a value, execute_script returns it to Python.

2. Step 2: Analyze the JS code 'return document.title'

   This returns the page title as a string, so the variable 'title' holds that string.

3. Final Answer:

   Prints the current page's title as a string -> Option C

4. Quick Check:

   execute_script returns JS value [OK]

Hint: Return keyword in JS returns value to Python [OK]

Common Mistakes:

• Assuming execute_script returns None always
• Confusing JS code string syntax
• Expecting execute_script to print automatically

4. Identify the error in this code snippet:

driver.execute_script(return document.body.style.backgroundColor = 'red')

medium

A. Incorrect method name, should be execute_js

B. Missing quotes around the JavaScript code string

C. Cannot change background color with JavaScript

D. Syntax error due to missing parentheses

Solution

1. Step 1: Check the argument passed to execute_script

   The JavaScript code must be passed as a string, but here it is passed without quotes.

2. Step 2: Confirm method name and JS validity

   The method name is correct and changing background color with JS is valid.

3. Final Answer:

   Missing quotes around the JavaScript code string -> Option B

4. Quick Check:

   JS code must be a quoted string [OK]

Hint: Always wrap JS code in quotes for execute_script [OK]

Common Mistakes:

• Forgetting quotes around JS code
• Thinking method name is wrong
• Believing JS cannot change styles

5. You want to scroll the page down by 500 pixels using Selenium's JavaScript executor in Python. Which code snippet correctly does this?

hard

A. driver.execute_script('window.scrollTo(500, 0)')

B. driver.execute_script('scrollTo(0, 500)')

C. driver.execute_script('scrollBy(500, 0)')

D. driver.execute_script('window.scrollBy(0, 500)')

Solution

1. Step 1: Understand scrolling methods in JavaScript

   window.scrollBy(x, y) scrolls by x and y pixels relative to current position.

2. Step 2: Identify correct parameters for scrolling down

   To scroll down 500 pixels, x=0 and y=500 is correct.

3. Final Answer:

   driver.execute_script('window.scrollBy(0, 500)') -> Option D

4. Quick Check:

   scrollBy(0, 500) scrolls down 500px [OK]

Hint: Use window.scrollBy(0, pixels) to scroll down [OK]

Common Mistakes:

• Swapping x and y values
• Using scrollTo instead of scrollBy incorrectly
• Passing wrong parameters causing horizontal scroll