How to force the browser to reload cached CSS/JS files?

Question

I have noticed that some browsers (in particular, Firefox and Opera) are very zealous in using cached copies of .css and .js files, even be

Answer 1

Just use server side code to add the date of the file... that way it WILL be cached and only reloaded when the file changes

In ASP.NET

This can be simplified to:

By adding an extension method to your project to extend Page:

public static class Extension_Methods
{
    public static string ResolveClientUrlUnique(this System.Web.UI.Page oPg, string sRelPath)
    {
        string sFilePath = oPg.Server.MapPath(sRelPath);
        string sLastDate = System.IO.File.GetLastWriteTime(sFilePath).ToString();
        string sDateHashed = System.Text.RegularExpressions.Regex.Replace(sLastDate, "[^0-9]", "");

        return oPg.ResolveClientUrl(sRelPath) + "?d=" + sDateHashed;
    }
}