Support mangling toplevel names

Close #127

README.md

@@ -141,12 +141,19 @@ input files from the command line.
 
 ## Mangler options
 
-To enable the mangler you need to pass `--mangle` (`-m`).  Optionally you
-can pass `-m sort=true` (we'll possibly have other flags in the future) in order
-to assign shorter names to most frequently used variables.  This saves a few
-hundred bytes on jQuery before gzip, but the output is _bigger_ after gzip
-(and seems to happen for other libraries I tried it on) therefore it's not
-enabled by default.
+To enable the mangler you need to pass `--mangle` (`-m`).  The following
+(comma-separated) options are supported:
+
+- `sort` — to assign shorter names to most frequently used variables.  This
+  saves a few hundred bytes on jQuery before gzip, but the output is
+  _bigger_ after gzip (and seems to happen for other libraries I tried it
+  on) therefore it's not enabled by default.
+
+- `toplevel` — mangle names declared in the toplevel scope (disabled by
+  default).
+
+- `eval` — mangle names visible in scopes where `eval` or `when` are used
+  (disabled by default).
 
 When mangling is enabled but you want to prevent certain names from being
 mangled, you can declare those names with `--reserved` (`-r`) — pass a

lib/scope.js

@@ -57,7 +57,7 @@ function SymbolDef(scope, index, orig) {
 
 SymbolDef.prototype = {
     unmangleable: function(options) {
-        return this.global
+        return (this.global && !(options && options.toplevel))
             || this.undeclared
             || (!(options && options.eval) && (this.scope.uses_eval || this.scope.uses_with));
     },
@@ -346,9 +346,10 @@ AST_Symbol.DEFMETHOD("global", function(){
 
 AST_Toplevel.DEFMETHOD("_default_mangler_options", function(options){
     return defaults(options, {
-        except : [],
-        eval   : false,
-        sort   : false
+        except   : [],
+        eval     : false,
+        sort     : false,
+        toplevel : false
     });
 });