Waiting for AJAX calls in WebDriver C#

I was trying to work out how to wait for AJAX calls to complete in C# WebDriver before continuing a test.

Whilst I believe that your UI should visually indicate that AJAX activity is occurring (such as a spinner) and in this case you should be able to wait until such an indicator changes, if you don’t have a visual indicator and you use JQuery for your AJAX calls, you can use a JavaScript call to jQuery.active to determine if there are any active AJAX requests, and wait until this value is zero.

I wrapped this into a WebDriver extension method on Driver, so you can call it like this:

Driver.FindElement(By.Id("name")).Set("Alister");
Driver.WaitForAjax();
Driver.FindElement(By.Id("next")).Click();

The actual extension method looks like this:

public static void WaitForAjax(this IWebDriver driver, int timeoutSecs = 10, bool throwException=false)
{
  for (var i = 0; i < timeoutSecs; i++)
  {
    var ajaxIsComplete = (bool)(driver as IJavaScriptExecutor).ExecuteScript("return jQuery.active == 0");
    if (ajaxIsComplete) return;
    Thread.Sleep(1000);
  }
  if (throwException)
  {
    throw new Exception("WebDriver timed out waiting for AJAX call to complete");
  }
}

I hope you find this helpful if you’re ever in the same situation.

Using WebDriver to automatically check for JavaScript errors on every page

Update: please see my newer post on this that doesn’t require changes to your application.


One of the benefits of using a page-object model is that you can perform certain actions on every page in your application that you visit, such as checking for accessibility.

One such check is automatically checking for JavaScript errors on page load. There’s a couple of approaches out there, one involves copying and pasting a small snippet of JavaScript into each page. Since our application we are working on uses a standard template for every page, we simply add some JavaScript to the common page header that is the first thing to load on the page, and catches any JavaScript errors that occur:

define(["amdUtils/string/interpolate"], function(interpolate) {
    window.jsErrors = [];

    window.onerror = function (errorMessage, url, lineNumber) {
        var message = interpolate("Error: [{{0}}], url: [{{1}}], line: [{{2}}]", [errorMessage, url, lineNumber]);
        window.jsErrors.push(message);
        return false;
    };
});

It’s then a matter of checking the jsErrors each time we visit a page, this is example C# code we use in the base page class for every page.

var js = driver as IJavaScriptExecutor;
ICollection javascriptErrors = null;
for (var i = 0; i < 20; i++)
{
  javascriptErrors = js.ExecuteScript("return window.jsErrors") as ICollection;
  if (javascriptErrors != null) break;
  System.Threading.Thread.Sleep(1000);
}
Assert.IsNotNull(javascriptErrors, "Can't seem to load JavaScript on the page to find JavaScript errors. Check that JavaScript is enabled.");
var javaScriptErrorsAsString = javascriptErrors.Cast<string>().Aggregate("", (current, error) => current + (error + ", "));
Assert.AreEqual("", javaScriptErrorsAsString, "Found JavaScript errors on page load: " + javaScriptErrorsAsString);

This code waits until it can read the jsErrors on the page. If it can’t, it means that JavaScript didn’t load and this is an error. Once it gets the jsErrors, it checks that there are none.

This code has been very useful for us. It has caught a number of JavaScript errors, and is especially great for finding cross browser JavaScript issues, as we run our acceptance tests in 5 different browsers.