Is there a way to transform a page loaded by HtmlUnit before it starts executing javascript?

Question

First I would like to describe the motivation for my question.

I have a complex web page to test with Selenium + HtmlUnit, which launches diverse javascript scripts. The problem which I describe should be quite common.

On the page there is a button to which jQuery binds a click callback (click event handler) after the page is loaded. There is an explicit Wait (this is a Selenium term) for the button to become clickable in the test code. So as soon as the button becomes clickable, it gets clicked by Selenium. Often, however, this happens before jQuery manages to attach to the button the click event handler. In this case the Selenium test fails.

What I thought to do is to preprocess the web page accessed by HtmlUnit before javascript starts executing on the page, injecting some <script>myownscript()</script> at the beginning of the page (so that it executes before any other script on that page). Then I would be able to know, controlling certain conditions in the Selenium test code, when exactly the attaching of the click event handler has happened (how I exactly do this, depends on the details of the application). If I make Selenium click the button then, the presence of the click event handler will be guaranteed, and the test would proceed further as planned - with no errors due to the missing click event handler.

Let us leave apart the question whether the idea is a good or a bad one (a much simpler one, of course, would be just introducing a large enough delay in the Selenium test code before trying to click the problematic button, but then there might be a problem with the overall duration of tests, because the problem I described is present on many pages of the application being tested). Are there some hooks in Selenium/HtmlUnit which permit to preprocess the page fetched from the server, injecting a script as I described, before javascript starts executing on the page?

Answer 1

In this case, you can use JavaScriptExecutor. You can add a function to do anything you want in the String script .

WebElement button = driver.findElement(By.id("my-button"));
JavascriptExecutor jsExe = ((JavascriptExecutor) driver);
String script = "console.log(arguments[0].id); return arguments[0].id";
Object oj = jsExe.executeScript(script, button);
String txt = oj.toString();
System.out.println(txt);

Please be careful if you want to use aycn such as setTimeout(), it will return immediately. See an example for async method in my answer at: method execute_script don't wait end of script to return value with selenium in python