Disable Alert box javascript in c# webbrowser control

Question

I have seen many articles or forums giving the following solution..but this solution is not going to work because after around 15 mins or sometimes after a few hours alert boxes will appear again, but I think timing is not an issue. I put this code inside a WebBrowserDocumentCompletedEventHandler.

And then I tried the following: Create a infinite loop and check it every second, if does not contain window.alert = function () { } then add it again, this is to prevent the website got ajax remove the code I injected earlier.

It still fails. My system has 5 tabs, each tab has its own web browser. I do injected each browser upon complete loaded.

private void InjectAlertBlocker() {     HtmlElement head = webBrowser1.Document.GetElementsByTagName("head")[0];     HtmlElement scriptEl = webBrowser1.Document.CreateElement("script");     IHTMLScriptElement element = (IHTMLScriptElement)scriptEl.DomElement;     string alertBlocker = "window.alert = function () { }";     element.text = alertBlocker;     head.AppendChild(scriptEl); }