Aptana got a nice feature that does the opposite of "format". It "minifies" the javascript code, to make it more compact.
A code like this:
function hello( id ){
  if (id > 0){
    $("#f" + id).attr('target', null);
  }
}
turns into this:
function hello(id){if(id>0){$("#f"+id).attr('target',null);}}

Not too hard to accomplish imo. it's not rewriting variables, it's not "packing" the code, it's just inlining/trimming
spaces.