When using Selenium for automated testing or data capture, sometimes the value of the input box (input) cannot be obtained through the regular `get_attribute("value")` method. Although the specific value is displayed on the page and is visible in the "Computed Properties" or "Accessibility" panel of the browser's developer tools, the direct Selenium method may return an empty string or an incorrect value. This article will introduce in detail how to use the JavaScript executor to successfully obtain the values ??of these "hidden" input boxes by temporarily modifying element attributes.

Understanding the question: Why do conventional methods fail?

In web automation, we usually use element.get_attribute("value") to get the current value of the element. However, in some specific scenarios, even if the input box visually displays content, this method may return an empty string, a default value (such as "---"), or an incorrect value. This usually happens when:

1. Elements are disabled or readonly : When an input box is set to disabled or readonly, its value attribute may not be fully exposed by the DOM to regular Selenium queries, or its displayed value may be dynamically rendered by JavaScript rather than directly stored in the value attribute.
2. Values ??are dynamically rendered through CSS or JavaScript : Some complex web applications may display values ??through CSS pseudo-elements, JavaScript calculations, or custom components instead of directly updating the value attribute of the HTML element.
3. Shadow DOM or Custom Elements : In these more advanced scenarios, standard DOM queries may not be able to directly touch the internal values.

When the "Computed Properties" or "Accessibility" panel of the developer tools displays the correct value, but get_attribute("value") fails, this usually implies that the value is calculated by the browser rendering engine or controlled by JavaScript, rather than being stored directly in an HTML attribute.

Common failed attempts

Faced with the above problems, many automation engineers will try the following methods, but often without success:

• element.get_attribute("innerHTML") : For elements, innerHTML is usually empty because it contains no child elements.
• element.text : The text attribute is mainly used to obtain the visible text content. For input boxes, its value is usually not available.
• element.get_attribute("value") : This is the most standard way to get the value of the input box, but in this problem scenario, it returns an incorrect value (such as "---").
• element.get_property("value") : get_property is used to get JavaScript attributes. It usually behaves similarly to get_attribute, but it also failed to work for this problem.

The failure of these attempts showed that we need a more direct, lower-level way to interact with the DOM.

Solution: Use JavaScript executors to modify element state

When the standard Selenium method cannot obtain the value, we can use Selenium's execute_script method to directly execute the JavaScript code. Through JavaScript, we can manipulate DOM elements more flexibly, including modifying their attributes.

For the problem that the value of the input box cannot be obtained, a common and effective strategy is to temporarily remove or modify the attribute that causes the value to be invisible (such as disabled or readonly), and then try to obtain the value attribute again.

Implementation steps

1. Locate the target element : Use Selenium's locator (such as By.XPATH, By.ID) to accurately find the target input box.
2. Execute JavaScript to modify attributes : Use the driver.execute_script() method to execute JavaScript code and set the disabled or readonly attribute of the element to an empty string or false, thereby making it operable.
3. Short wait (optional but recommended) : In some dynamic pages, the DOM may take a short time to update. Adding a short wait (such as time.sleep()) can ensure that the property modification has taken effect.
4. Get the value attribute again : At this point, using element.get_attribute("value") should be able to successfully obtain the correct value.

Sample code

Assuming that the id of the target input box is exttemp, the following is the specific Python Selenium implementation:

 import time
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 WebDriver (such as Chrome)
driver = webdriver.Chrome()
# driver.get("your target URL") # Replace with the actual web page URL

try:
    # Assume the page is loaded and the target element exists # Wait for the element to be visible target_element_locator = (By.XPATH, "//input[@id='exttemp']")
    element = WebDriverWait(driver, 10).until(
        EC.visibility_of_element_located(target_element_locator)
    )

    # Step 1 & 2: Use JavaScript to remove or modify the disabled attribute # Note: This assumes that the problem is caused by the disabled attribute.
    # If it is readonly, change it to "document.getElementById('exttemp').readOnly = false;"
    # Or remove the attribute directly "document.getElementById('exttemp').removeAttribute('disabled');"
    driver.execute_script("document.getElementById('exttemp').disabled='';")

    # Step 3: Wait briefly to ensure the DOM is updated time.sleep(1)

    # Step 4: Get the value attribute of the element again # At this time, since the disabled attribute has been removed, get_attribute("value") should be able to get the correct value retrieved_value = element.get_attribute("value")
    print(f"The input box value successfully obtained: {retrieved_value}")

except Exception as e:
    print(f"An error occurred: {e}")

finally:
    #Close the browser driver.quit()

Code explanation

• driver.execute_script("document.getElementById('exttemp').disabled='';"): This line of code is the heart of the solution. It instructs the browser to execute JavaScript.
  • document.getElementById('exttemp'): Get the target HTML element by ID.
  • .disabled='': Set the disabled attribute of the element to an empty string. In HTML, setting the disabled attribute to the empty string or any non-empty value (like disabled="false" will actually still disable the element) will enable the element. A more rigorous approach is to removeAttribute('disabled') or set element.disabled = false;.
• time.sleep(1): Provides a buffer time of 1 second to allow the browser to complete DOM updates. In actual projects, it can be adjusted or replaced with a more intelligent explicit wait based on page response speed.
• element.get_attribute("value"): After the disabled attribute is removed, call this method again to obtain the correct input box value.

Things to note and best practices

1. Modify DOM with caution : Modifying DOM properties through JavaScript will change the actual state of the page. In automated testing, this is usually acceptable, but when scraping, make sure that this modification does not negatively impact subsequent operations or page behavior.
2. Target attribute judgment : Before executing JavaScript to modify attributes, it is best to confirm which attribute is causing the problem (for example, disabled or readonly). This can be determined by inspecting the element's properties through the developer tools.
3. Explicit wait instead of time.sleep : Although time.sleep is simple and easy to use, in a production environment, it is more recommended to use WebDriverWait combined with expected_conditions to wait for DOM state changes, such as waiting for a certain attribute to disappear or change.
4. Locator accuracy : Ensure that locators such as By.ID or By.XPATH find the target element accurately. Inaccurate locators can cause scripts to fail.
5. Applicable scenarios : This method is mainly suitable for situations where the value cannot be obtained directly due to disabled, readonly and other attributes. For more complex scenes, such as elements inside Shadow DOM or elements rendered entirely by Canvas, a more specialized solution may be required.

Summarize

When Selenium's regular methods cannot obtain the real value of the input box, especially when the developer tool shows that the value exists in "Computed Properties", executing JavaScript code through driver.execute_script() to temporarily modify element attributes (such as removing disabled or readonly) is a very effective solution. This approach allows us to bypass the limitations of certain web elements under the standard Selenium interface and interact directly with the DOM to successfully extract the required data. When applying this technique, it is important to be aware of its impact on page state and incorporate explicit waits to improve the robustness of your script.

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