Add --mangle-regex option

README.md

@@ -132,6 +132,7 @@ The available options are:
   --reserve-domprops            Make (most?) DOM properties reserved for
                                 --mangle-props
   --mangle-props                Mangle property names
+  --mangle-regex                Only mangle property names matching the regex
   --name-cache                  File to hold mangled names mappings
 ```
 
@@ -251,6 +252,10 @@ A default exclusion file is provided in `tools/domprops.json` which should
 cover most standard JS and DOM properties defined in various browsers.  Pass
 `--reserve-domprops` to read that in.
 
+You can also use a regular expression to define which property names should be
+mangled.  For example, `--mangle-regex="^_"` will only mangle property names
+that start with an underscore.
+
 When you compress multiple files using this option, in order for them to
 work together in the end we need to ensure somehow that one property gets
 mangled to the same name in all of them.  For this, pass `--name-cache

bin/uglifyjs

@@ -70,6 +70,7 @@ You need to pass an argument to this option to specify the name that your module
     .describe("reserved-file", "File containing reserved names")
     .describe("reserve-domprops", "Make (most?) DOM properties reserved for --mangle-props")
     .describe("mangle-props", "Mangle property names")
+    .describe("mangle-regex", "Only mangle property names matching the regex")
     .describe("name-cache", "File to hold mangled names mappings")
 
     .alias("p", "prefix")
@@ -375,10 +376,12 @@ async.eachLimit(files, 1, function (file, cb) {
     if (ARGS.mangle_props || ARGS.name_cache) (function(){
         var reserved = RESERVED ? RESERVED.props : null;
         var cache = readNameCache("props");
+        var regex = ARGS.mangle_regex ? new RegExp(ARGS.mangle_regex) : null;
         TOPLEVEL = UglifyJS.mangle_properties(TOPLEVEL, {
             reserved   : reserved,
             cache      : cache,
-            only_cache : !ARGS.mangle_props
+            only_cache : !ARGS.mangle_props,
+            regex      : regex
         });
         writeNameCache("props", cache);
     })();

lib/propmangle.js

@@ -64,7 +64,8 @@ function mangle_properties(ast, options) {
     options = defaults(options, {
         reserved : null,
         cache : null,
-        only_cache : false
+        only_cache : false,
+        regex : null
     });
 
     var reserved = options.reserved;
@@ -79,6 +80,8 @@ function mangle_properties(ast, options) {
         };
     }
 
+    var regex = options.regex;
+
     var names_to_mangle = [];
 
     // step 1: find candidates to mangle
@@ -149,6 +152,7 @@ function mangle_properties(ast, options) {
     }
 
     function should_mangle(name) {
+        if (regex && !regex.test(name)) return false;
         if (reserved.indexOf(name) >= 0) return false;
         return cache.props.has(name)
             || names_to_mangle.indexOf(name) >= 0;