bug when removing duplicated semicolon in for statement
Code before packing:
for(var myvar=0,t=0;;){}
Coder After packing
for(var myvar=0,t=0;){}
javascript error:
Uncaught SyntaxError: Unexpected token )
because the second semicolon is part from for statement.
It looks like this is a bug with packer itself. I tried that example on http://dean.edwards.name/packer/ and it does indeed introduce a syntax error. You should probably file this bug with the original package instead.
That said, I strongly recommend using a community-supported JavaScript minifier instead of packer. It'll be much better tested and will actually be supported (I'm not actually sure where to file bugs against packer). I personally recommend uglify, which I have been using for quite a while and haven't had any issues like this.