InsertScript for ASP.NET MVC

I recently had a situation where a custom control I was using in a page required jQuery.  Since I like the idea of keeping such controls self-contained, I added the usual <script type="text/javascript" src="jquery-1.2.6.min.js"></script> tag.

No problem – until I then loaded a page that included this control AND also had its own requirement for jQuery.  It seems that jQuery doesn’t like begin included twice, so I had a choice.  I could:

• Include jQuery once in the header (or wherever) of each page (i.e. in the Master Page), hence breaking the self-containment of my control, or;
• Write a helper method to keep track of which script files had been included in each page and hence allow a script file to only be included once per request.

It should come as no surprise (as otherwise there would be no point in this post) that I went for the second option.

The HttpContext object has an Items collection, and since the HttpContext has a lifetime of one request, we can use this Items collection to keep track of our included files.  Just add the following static method to a static class (Don’t you just love Extension Methods!):

public static string InsertScript(this HtmlHelper helper, string jsFile)
{
    const string RESID = "__resources";

    List<string> _resources = (List<string>)helper.ViewContext.HttpContext.Items[RESID];
    if (_resources == null)
    {
        _resources = new List<string>();
        helper.ViewContext.HttpContext.Items[RESID] = _resources;
    }

    string url = ScriptUrl(jsFile);
    if (!_resources.Contains(url.ToLower()))
    {
        _resources.Add(url.ToLower());
        return "<script type=\"text/javascript\" src=\"" + url + "\"></script>";
    }
    else
        return "";
}

Notice the call to ScriptUrl(jsFile) – this is just a static helper method to map javascript file names to the Scripts folder in my web app. It’s up to you whether you use such a method.

It’s now just a matter of calling this from your .aspx pages, replacing the usual
<script type="text/javascript" src="myjavascriptfile.js"></script>
with
<%= Html.InsertScript("myjavascriptfile.js") %>

Generic List ContainsOneOf

I needed a function that would return a boolean indicating if any of the values from one list appeared in another list.  I love extension methods…

public static bool ContainsOneOf<T>(this IList<T> first, IList<T> second)
{
    foreach (T item in first)
    {
        if (second.Contains(item))
            return true;
    }
    return false;
}

Remember to place this method in a public static class.