How to invoke custom Javascript in System.Windows.Forms.WebBrowser?

Question

I'm loading third party webpage that contains following code

<script type="text/javascript">
onDomReady(function() { some_code1; });
</script>

into WebBrowser component. After some_code1 had executed I need to do some manipulations with Dom that will make some_code1 invalid. The question is how to determine that some_code1 had executed?

I cant't do

private void web_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    DoRequiredManipulations();
}

Since this event will occur before some_code1 has executed and will make it invalid.

Also I can't do

private void web_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    web.Document.InvokeScript("doSome_code1");
    DoRequiredManipulations();
}

Since some_code1 is declared as an anonymous function.

It seems that the only way to do it is this:

private void web_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    var script = GetScriptText(web.DocumentText);
    //execute script in webbrowser
    DoRequiredManipulations();
}

The problem is that I don't know how to execute this script in webbrowser. I had tried web.Navigate("javascript: " + script); but it doesn't work correctly.