I have source codes of some javascript projects and I want to know which of them are compiled using Google's Closure compiler.
There are a couple of quirks that you can look for that may be unique to the Closure Compiler:
(1) the closure compiler rewrites all "while" loops as "for" loops. So if you see a "while" loop, it isn't optimized by the Closure Compiler (it might still be processed by the Closure Compiler, but it hasn't been optimized)
(2) using the default optimization options, the Closure Compiler breaks lines at about 500 characters. If the average line length is significantly less than that or greater than that, it may not be optimized by the compiler.
(3) some constants, the compiler rewrites "undefined", "true" and "false" are rewritten to "void 0" "!0" and "!1" respectively, if you see the others it is NOT optimized by the Closure Compiler (but doesn't tell you that it has been).
Other characteristics may exist but it would depend on the version of the compiler you are using.