Fix inner numeric indices incorrectly altering parent req.params

History.md

@@ -2,6 +2,7 @@ unreleased
 ==========
 
   * Fix infinite loop condition using `mergeParams: true`
+  * Fix inner numeric indices incorrectly altering parent `req.params`
 
 4.13.2 / 2015-07-31
 ===================

lib/router/index.js

@@ -596,7 +596,7 @@ function mergeParams(params, parent) {
     }
   }
 
-  return mixin(parent, params);
+  return mixin(obj, params);
 }
 
 // restore obj props after function

test/app.router.js

@@ -354,6 +354,26 @@ describe('app.router', function(){
       .get('/user/tj')
       .expect(200, '[["name","tj"]]', done);
     })
+
+    it('should restore req.params', function(done){
+      var app = express();
+      var router = new express.Router({ mergeParams: true });
+
+      router.get('/user:(\\w+)/*', function (req, res, next) {
+        next();
+      });
+
+      app.use('/user/id:(\\d+)', function (req, res, next) {
+        router(req, res, function (err) {
+          var keys = Object.keys(req.params).sort();
+          res.send(keys.map(function(k){ return [k, req.params[k]] }));
+        });
+      });
+
+      request(app)
+      .get('/user/id:42/user:tj/profile')
+      .expect(200, '[["0","42"]]', done);
+    })
   })
 
   describe('trailing slashes', function(){