JavaScript executor basics in Selenium Python - Build an Automation Script

Use JavaScript executor to scroll and get page title

Preconditions (2)

Step 1: Open the browser and navigate to https://example.com

Step 2: Use JavaScript executor to scroll down 500 pixels vertically

Step 3: Use JavaScript executor to get the page title

Step 4: Verify the page title matches 'Example Domain'

✅ Expected Result: The page scrolls down 500 pixels and the page title is 'Example Domain'

Automation Requirements - Selenium with Python

Assertions Needed:

Verify the page title is exactly 'Example Domain'

Best Practices:

Use explicit waits to ensure page is loaded before executing JavaScript

Use driver.execute_script() for JavaScript execution

Avoid hardcoded waits like time.sleep()

Use clear and descriptive variable names

Automated Solution

Selenium Python

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

# Setup Chrome WebDriver
service = Service()
driver = webdriver.Chrome(service=service)

try:
    driver.get('https://example.com')

    # Wait until the page title contains 'Example Domain'
    WebDriverWait(driver, 10).until(EC.title_contains('Example Domain'))

    # Scroll down 500 pixels vertically using JavaScript executor
    driver.execute_script('window.scrollBy(0, 500);')

    # Get the page title using JavaScript executor
    page_title = driver.execute_script('return document.title;')

    # Assert the page title is exactly 'Example Domain'
    assert page_title == 'Example Domain', f"Expected title 'Example Domain' but got '{page_title}'"

finally:
    driver.quit()

This script opens the browser and navigates to https://example.com.

It waits explicitly until the page title contains 'Example Domain' to ensure the page is fully loaded.

Then it uses driver.execute_script() to scroll down 500 pixels vertically.

Next, it uses JavaScript executor again to get the page title directly from the browser.

Finally, it asserts that the page title exactly matches 'Example Domain'.

The try-finally block ensures the browser closes even if the test fails.

Common Mistakes - 4 Pitfalls

Using time.sleep() instead of explicit waits

Not using driver.execute_script() for JavaScript execution

Not verifying the page title after getting it with JavaScript

Using vague or incorrect selectors for elements when not needed

Bonus Challenge

Now add data-driven testing to scroll different pixel values: 100, 300, and 700

Show Hint

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