Modifying element attributes with JS in Selenium Python - Build an Automation Script

Modify an element's attribute using JavaScript in Selenium

Preconditions (2)

Step 1: Open the target web page in the browser

Step 2: Locate the element with id 'username-input'

Step 3: Use JavaScript to change the element's 'placeholder' attribute to 'Enter your username'

Step 4: Verify that the placeholder attribute of the element is updated correctly

✅ Expected Result: The input element with id 'username-input' has its placeholder attribute changed to 'Enter your username'

Automation Requirements - Selenium with Python

Assertions Needed:

Verify the placeholder attribute of the element is 'Enter your username'

Best Practices:

Use explicit waits to ensure the element is present before interacting

Use Selenium's execute_script method to run JavaScript

Use By.ID locator for element identification

Use assert statements for verification

Automated Solution

Selenium Python

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

# Initialize the WebDriver (example with Chrome)
driver = webdriver.Chrome()

try:
    # Open the target web page
    driver.get('https://example.com')

    # Wait until the element with id 'username-input' is present
    wait = WebDriverWait(driver, 10)
    element = wait.until(EC.presence_of_element_located((By.ID, 'username-input')))

    # Use JavaScript to modify the placeholder attribute
    driver.execute_script("arguments[0].setAttribute('placeholder', 'Enter your username')", element)

    # Verify the placeholder attribute is updated
    updated_placeholder = element.get_attribute('placeholder')
    assert updated_placeholder == 'Enter your username', f"Expected placeholder to be 'Enter your username' but got '{updated_placeholder}'"

finally:
    driver.quit()

This script starts by opening the browser and navigating to the target page.

It waits explicitly for the element with id 'username-input' to be present to avoid errors.

Then it uses Selenium's execute_script method to run JavaScript that changes the element's placeholder attribute.

Finally, it retrieves the updated attribute and asserts it matches the expected value.

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

Common Mistakes - 4 Pitfalls

{'mistake': 'Using time.sleep instead of explicit waits', 'why_bad': 'It can cause flaky tests because the element might not be ready when the sleep ends.', 'correct_approach': "Use Selenium's explicit waits like WebDriverWait with expected_conditions."}

Using incorrect locator strategies like XPath with absolute paths

Not verifying the attribute change after executing JavaScript

Not closing the browser after test execution

Bonus Challenge

Now add data-driven testing to modify the placeholder attribute with three different values: 'Enter username', 'Type your user ID', and 'User login here'.

Show Hint

Practice

1. What does the following Selenium Python code do?
driver.execute_script("arguments[0].setAttribute('disabled', 'true')", element)

easy

A. It changes the element's text to 'true'.

B. It enables the web element by removing the 'disabled' attribute.

C. It disables the web element by setting its 'disabled' attribute to true.

D. It deletes the element from the page.

Solution

1. Step 1: Understand the JavaScript command

   The JavaScript code uses setAttribute to add or change the 'disabled' attribute of the element to 'true'.

2. Step 2: Effect on the web element

   Setting 'disabled' to 'true' makes the element disabled, meaning user interaction is blocked.

3. Final Answer:

   It disables the web element by setting its 'disabled' attribute to true. -> Option C

4. Quick Check:

   setAttribute('disabled', 'true') disables element [OK]

Hint: setAttribute('disabled', 'true') disables element [OK]

Common Mistakes:

• Confusing 'disabled' attribute with changing text content
• Thinking it removes the element
• Assuming it enables the element instead

2. Which of the following is the correct syntax to change an element's attribute 'class' to 'active' using Selenium Python's execute_script?

easy

A. driver.execute_script("arguments[0].setAttribute('class', 'active')", element)

B. driver.execute_script("element.setAttribute('class', 'active')")

C. driver.execute_script("arguments.setAttribute('class', 'active')", element)

D. driver.execute_script("arguments[0].setAttribute('class' = 'active')", element)

Solution

1. Step 1: Identify correct use of arguments in execute_script

   In Selenium, arguments[0] refers to the first argument passed after the script string, which is the element.

2. Step 2: Check JavaScript syntax for setAttribute

   The correct syntax is setAttribute('attributeName', 'value'). driver.execute_script("arguments[0].setAttribute('class', 'active')", element) uses this correctly with arguments[0].

3. Final Answer:

   driver.execute_script("arguments[0].setAttribute('class', 'active')", element) -> Option A

4. Quick Check:

   Use arguments[0].setAttribute('class', 'active') [OK]

Hint: Use arguments[0] for element in execute_script [OK]

Common Mistakes:

• Using 'element' directly inside the script string
• Wrong JavaScript syntax like '=' inside setAttribute
• Using 'arguments' without index

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

element = driver.find_element(By.ID, 'submit-btn')
driver.execute_script("arguments[0].setAttribute('data-test', 'passed')", element)
attr_value = element.get_attribute('data-test')
print(attr_value)

medium

A. SyntaxError

B. data-test

C. None

D. passed

Solution

1. Step 1: Modify attribute using JavaScript

   The script sets the 'data-test' attribute of the element to 'passed'.

2. Step 2: Retrieve the attribute value

   Calling get_attribute('data-test') fetches the updated value, which is 'passed'.

3. Final Answer:

   passed -> Option D

4. Quick Check:

   setAttribute then get_attribute returns new value [OK]

Hint: get_attribute returns updated attribute after JS change [OK]

Common Mistakes:

• Expecting None because attribute was not originally present
• Confusing attribute name with value
• Thinking JavaScript changes don't reflect in Selenium

4. Identify the error in the following code snippet that tries to change an element's 'title' attribute:

element = driver.find_element(By.CSS_SELECTOR, '.btn')
driver.execute_script("arguments[0].setAttribute('title', title)", element)

medium

A. The variable 'title' is not defined in the JavaScript context.

B. The element locator is incorrect.

C. The setAttribute method is misspelled.

D. execute_script cannot modify attributes.

Solution

1. Step 1: Analyze JavaScript string in execute_script

   The script uses 'title' as a variable inside the string, but it is not defined in JavaScript context.

2. Step 2: Understand variable passing in execute_script

   To pass a Python variable, it must be included as an argument and referenced via arguments[1] or similar.

3. Final Answer:

   The variable 'title' is not defined in the JavaScript context. -> Option A

4. Quick Check:

   JS variables must be passed explicitly [OK]

Hint: Pass variables as arguments, not inline strings [OK]

Common Mistakes:

• Using Python variables directly inside JS string
• Ignoring need for arguments[n] in execute_script
• Assuming locator error without checking script

5. You want to toggle a checkbox's 'checked' attribute using Selenium Python and JavaScript. Which code snippet correctly toggles the checkbox state?

hard

A. driver.execute_script("arguments[0].setAttribute('checked', !arguments[0].checked)", checkbox_element)

B. driver.execute_script("arguments[0].checked = !arguments[0].checked", checkbox_element)

C. driver.execute_script("arguments[0].checked = 'false'", checkbox_element)

D. driver.execute_script("arguments[0].removeAttribute('checked')", checkbox_element)

Solution

1. Step 1: Understand checkbox 'checked' property vs attribute

   The 'checked' property is a boolean that controls checkbox state; toggling it flips the state.

2. Step 2: Evaluate each option's effect

   driver.execute_script("arguments[0].checked = !arguments[0].checked", checkbox_element) uses JavaScript to toggle the boolean property correctly. driver.execute_script("arguments[0].setAttribute('checked', !arguments[0].checked)", checkbox_element) tries to set attribute with a boolean, which converts to string and may not work as expected. driver.execute_script("arguments[0].checked = 'false'", checkbox_element) sets 'checked' to string 'false', which does not uncheck. driver.execute_script("arguments[0].removeAttribute('checked')", checkbox_element) removes 'checked' attribute but does not toggle back on.

3. Final Answer:

   driver.execute_script("arguments[0].checked = !arguments[0].checked", checkbox_element) -> Option B

4. Quick Check:

   Toggle boolean property 'checked' to flip checkbox [OK]

Hint: Toggle checkbox by flipping 'checked' boolean property [OK]

Common Mistakes:

• Using setAttribute with boolean values
• Setting 'checked' to string 'false' instead of boolean
• Removing attribute without toggling back