How2: what event to hook in HttpModule for putting js links into head element

I want to have HttpModule to inject javascripts, css links into HEAD element from some simple config data. I am not sure which event I should hook?

Curently I use
- context.PreRequestHandlerExecute for changing the masterpage dynamically
- Context.BeginRequest for SEO optimalization

There is some help at http://stackoverflow.com/questions/441421/httpmodule-event-execution-order

Thanks for any tip. Cheers, X.

From stackoverflow

• An HttpHandler would be a better choice for this type of functionality. Here is an example which goes over combining css and javascript files; it is not exactly what you are looking for but should get you headed in the right direction: http://www.codeproject.com/KB/aspnet/HttpCombine.aspx

  Xabatcha : Thanks for tip.It is interesting implementation.

• using System;
  using System.Web;
  using System.Web.UI;
  
  namespace YourNamespace
  {
      public class YourModule : IHttpModule
      {
          public void Init(HttpApplication context)
          {
              context.PreRequestHandlerExecute += Application_PreRequestHandlerExecute;
          }
  
          private void Application_PreRequestHandlerExecute(object sender, EventArgs e)
          {
              Page page = HttpContext.Current.CurrentHandler as Page;
              if (page != null)
              {
                  string script = "/js/jquery.1.3.2.min.js";
                  if (page.Header != null)
                  {
                      string scriptTag = String.Format("<script language=\"javascript\" type=\"text/javascript\" src=\"{0}\"></script>\n", script);
                      page.Header.Controls.Add(new LiteralControl(scriptTag));
                  }
                  else if (!page.ClientScript.IsClientScriptIncludeRegistered(page.GetType(), script))
                      page.ClientScript.RegisterClientScriptInclude(page.GetType(), script, script);
              }
          }
  
          public void Dispose() { }
      }
  }
  

  ASP.Net Lifecycle: http://msdn.microsoft.com/en-us/library/ms178473.aspx

  Xabatcha : Thanks for example. I use similar implementation. I was just more cirious about using right event. E.g. in my case I use context.PreRequestHandlerExecute += ContextPreRequestHandlerExecute; and then page.PreLoad += PagePreLoad; In PagePreLoad then set the js element and works very well. But is it right?

  Chad Grant : Yes, that is the correct event. I haven't done this in a HttpModule, but I do this in my base Page class. I'll post another answer to show you how I did it.

• Here's how I implemented what you are doing without a HttpModule. I didn't like the httpmodule idea because if I forgot to register it and it wasn't running, my app wouldn't work and it would have been a non obvious bug. The page absolutely needs the JS included so I decided to put it in the base Page class of the project.

  I implemented this years ago, and wanted to be able to include more than just scripts, it supports css, meta tags, etc.... I forget why I used Page.Header.Controls.Add instead of just Page.ClientScript.RegisterClientScriptInclude but there was a reason.

  using System;
  using System.Collections.Generic;
  using System.Web;
  using System.Web.UI;
  
  namespace YourNamespace
  {
      public class HeaderIncludesManager
      {
          private List<string> m_IncludedFiles = new List<string>();
  
          public void IncludeScript(string s)
          {
              IncludeScript(s, null);
          }
  
          public bool IsIncluded(string file)
          {
              return (m_IncludedFiles.Find(s => s.Equals(file, StringComparison.InvariantCultureIgnoreCase)) != null);
          }
  
          public void IncludeScript(string script, string condition)
          {
              Page page = HttpContext.Current.CurrentHandler as Page;
              if (!IsIncluded(script) || page == null)
                  return;
  
              string scriptFile = string.Format("/{0}/{1}?v={2}", MyConfig.JSDir, script, MyConfig.BuildNumber);
              if (page.Header != null)
              {
                  string scriptTag = String.Format("<script language=\"javascript\" type=\"text/javascript\" src=\"{0}\"></script>\n", scriptFile);
                  if (!String.IsNullOrEmpty(condition))
                      scriptTag = String.Format("<!--[{0}]><script language=\"javascript\" type=\"text/javascript\" src=\"{1}\"></script><![endif]-->\n", condition, scriptFile);
  
                  page.Header.Controls.Add(new LiteralControl(scriptTag));
                  m_IncludedFiles.Add(script);
              }
              else if (!page.ClientScript.IsClientScriptIncludeRegistered(GetType(), scriptFile))
              {
                  page.ClientScript.RegisterClientScriptInclude(GetType(), scriptFile, scriptFile);
                  m_IncludedFiles.Add(script);
              }
          }
  
          public void IncludeCss(string css)
          {
              Page page = HttpContext.Current.CurrentHandler as Page;
              if (!IsIncluded(css) || page == null)
                  return;
  
              string cssfile = string.Format("/{0}/{1}?v={2}", MyConfig.CssDir, css, MyConfig.BuildNumber);
              if (page.Header != null)
              {
                  ((Page)HttpContext.Current.CurrentHandler).Header.Controls.Add(new LiteralControl(String.Format("<link href=\"{0}\" rel=\"stylesheet\" type=\"text/css\" />\n", cssfile)));                    
                  m_IncludedFiles.Add(css);
              }
          }
  
          public void IncludeJQuery()
          {
              IncludeScript("jquery-1.2.3.min.js");
          }
  
          public void IncludeJQueryUI()
          {
              IncludeJQuery();
              IncludeScript("jquery.ui.1.0.min.js");
              IncludeCss("jquery-theme.css");
          }
  
          public void IncludeFlotScripts()
          {
              IncludeJQuery();
              IncludeScript("flot/jquery.flot.js");
              IncludeScript("flot/excanvas.pack.js", "if IE");
          }
      }
  
      public class MyPage : Page
      {
          public HeaderIncludesManager HeaderIncludes = new HeaderIncludesManager();
      }
  
      public class MyControl : UserControl
      {
          public new MyPage Page
          {
              get
              {
                  return (MyPage)base.Page;
              }
          }
      }
  
      public class SomeControlThatNeedsScripts : MyControl
      {
          protected override void OnLoad(EventArgs e)
          {
              Page.HeaderIncludes.IncludeJQueryUI();
              base.OnLoad(e);
          }
      }
  }
  

  Xabatcha : What I like in this implementation is that it loads scripts,css only for specific pages. Which may be better in case of scripts, which are not used everywhere. Thanks.