Closure Compiler does not natively support Internet Explorer's conditional compilation, however it is still possible to use them in a limited way.

IE's conditional compilation can not be used directly, but they can be used in eval conditions. As an example, one common use is to detect Internet Explorer:

var is_ie = /*@cc_on!@*/false;

This can be rewritten to be compatible with Closure Compiler in this way:

var is_ie = eval("/*@cc_on!@*/false");

The rules for using this solution are the same for the use of eval in general.