[SOLVED] Selenium: How to Inject/execute a Javascript in to a Page before loading/executing any other scripts of the page?

Selenium: How to Inject/execute a Javascript in to a Page before loading/executing any other scripts of the page?

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!

Solution

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>
    ...