Bundling not working in MVC5 when I turn on release mode

This is the default behavior.

Bundling and minification is enabled or disabled by setting the value of the debug attribute in the compilation Element in the Web.config file.

http://www.asp.net/mvc/overview/performance/bundling-and-minification

The default Release Web.config transform removes the debug attribute like so:

<compilation xdt:Transform="RemoveAttributes(debug)" />

However, this will not cause the expected bundling behavior to occur. Instead, you must create a transform that literally sets the debug attribute to "false", like so:

<compilation debug="false" xdt:Transform="SetAttributes" />

The way that I get around this is to force it in the BundleConfig to do exactly what I want it to do. I don't think MVC4 had the same options with the config file (or I just never got them to work).

So this is what I have at the end of my RegisterBundles method:

#if DEBUG
BundleTable.EnableOptimizations = false;
#else
BundleTable.EnableOptimizations = true;
#endif

This way it's always there, plain to see. However, you do have to remember to put that in there when you're starting up the project, but that's not a huge deal.

If you're not familiar with these, the #if DEBUG is a preprocessor directives that tells the CLR to do what is in that block when the DEBUG build parameter is present (should only be present in DEBUG mode, though that can be changed from the Project Properties). If that variable is not present (Release mode, or any other mode), then it will do the other block.