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I'm using selenium python webdriver in order to browse some pages. I want to inject a javascript code in to a pages before any other Javascript codes get loaded and executed. On the other hand, I need my JS code to be executed as the first JS code of that page. Is there a way to do that by Selenium?
I googled it for a couple of hours, but I couldn't find any proper answer!
314
You an use selenium to do automated testing of web apps or websites, or just automate the web browser. It can automate both the desktop browser and the mobile browser. Selenium webdriver can execute Javascript. After loading a page, you can execute any javascript you want.
We can run Javascript in Selenium webdriver with Python. The Document Object Model communicates with the elements on the page with the help of Javascript. Selenium executes the Javascript commands by taking the help of the execute_script method.
Selenium has now supported Chrome Devtools Protocol (CDP) API, so , it is really easy to execute a script on every page load. Here is an example code for that:
driver.execute_cdp_cmd('Page.addScriptToEvaluateOnNewDocument', {'source': 'alert("Hooray! I did it!")'})
And it will execute that script for EVERY page load. More information about this can be found at:
69
Since version 1.0.9, selenium-wire has gained the functionality to modify responses to requests. Below is an example of this functionality to inject a script into a page before it reaches a webbrowser.
import os
from seleniumwire import webdriver
from gzip import compress, decompress
from urllib.parse import urlparse
from lxml import html
from lxml.etree import ParserError
from lxml.html import builder
script_elem_to_inject = builder.SCRIPT('alert("injected")')
def inject(req, req_body, res, res_body):
# various checks to make sure we're only injecting the script on appropriate responses
# we check that the content type is HTML, that the status code is 200, and that the encoding is gzip
if res.headers.get_content_subtype() != 'html' or res.status != 200 or res.getheader('Content-Encoding') != 'gzip':
return None
try:
parsed_html = html.fromstring(decompress(res_body))
except ParserError:
return None
try:
parsed_html.head.insert(0, script_elem_to_inject)
except IndexError: # no head element
return None
return compress(html.tostring(parsed_html))
drv = webdriver.Firefox(seleniumwire_options={'custom_response_handler': inject})
drv.header_overrides = {'Accept-Encoding': 'gzip'} # ensure we only get gzip encoded responses
Another way in general to control a browser remotely and be able to inject a script before the pages content loads would be to use a library based on a separate protocol entirely, eg: Chrome DevTools Protocol. The most fully featured I know of is playwright
45
If you want to inject something into the html of a page before it gets parsed and executed by the browser I would suggest that you use a proxy such as Mitmproxy.
6
If you cannot modify the page content, you may use a proxy, or use a content script in an extension installed in your browser. Doing it within selenium you would write some code that injects the script as one of the children of an existing element, but you won't be able to have it run before the page is loaded (when your driver's get() call returns.)
String name = (String) ((JavascriptExecutor) driver).executeScript(
"(function () { ... })();" ...
The documentation leaves unspecified the moment at which the code would start executing. You would want it to before the DOM starts loading so that guarantee might only be satisfiable with the proxy or extension content script route.
If you can instrument your page with a minimal harness, you may detect the presence of a special url query parameter and load additional content, but you need to do so using an inline script. Pseudocode:
<html>
<head>
<script type="text/javascript">
(function () {
if (location && location.href && location.href.indexOf("SELENIUM_TEST") >= 0) {
var injectScript = document.createElement("script");
injectScript.setAttribute("type", "text/javascript");
//another option is to perform a synchronous XHR and inject via innerText.
injectScript.setAttribute("src", URL_OF_EXTRA_SCRIPT);
document.documentElement.appendChild(injectScript);
//optional. cleaner to remove. it has already been loaded at this point.
document.documentElement.removeChild(injectScript);
}
})();
</script>
...
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