ASP.NET MVC4 Bundler and .min.js Files: A Common Problem

Using the ASP.NET MVC4 bundler, developers sometimes encounter a problem where minimized JavaScript files (.min.js) are excluded from bundles. Even if you correctly specify the .min.js file in BundleConfig, only the un-minimized version is included in the output.

For instance, a bundle might be defined to include ~/Scripts/jquery-1.8.0.js and ~/Scripts/jquery.tmpl.min.js. However, only jquery-1.8.0.js appears in the rendered HTML.

This happens because the BundleCollection's IgnoreList defaults to ignoring .min files when optimization is turned off. To fix this, you can either adjust the IgnoreList or rename your files.

Solutions:

1. Rename .min.js files: The simplest solution is to rename your minimized files to use the .js extension.

2. Modify RegisterBundles: A more robust approach involves modifying the RegisterBundles method to explicitly control which files are ignored. This allows you to include .min.js files even when optimization is disabled.

Corrected RegisterBundles Method:

public static void RegisterBundles(BundleCollection bundles)
{
    bundles.IgnoreList.Clear();
    AddDefaultIgnorePatterns(bundles.IgnoreList);

    // Explicitly ignore .min.js files ONLY when optimization is disabled.
    bundles.IgnoreList.Ignore("*.min.js", OptimizationMode.WhenDisabled);
}

By clearing the default IgnoreList and adding this custom rule, the bundler correctly handles .min.js files regardless of the optimization setting, ensuring that your minimized scripts are included in your bundles.