Add exposeAdditionalProperties option

README.md

@@ -30,7 +30,9 @@ app.use('/api', api);
 
 ### .use(errorHandler([options]))
 
-Currently no options.
+Options:
+
+- `exposeAdditionalProperties` - If truthy will expose any additional properties found on client errors.
 
 ### Errors
 

index.js

@@ -3,7 +3,9 @@ var statuses = require('statuses');
 
 var production = process.env.NODE_ENV === 'production';
 
-module.exports = function () {
+module.exports = function (options) {
+  options = options || {}
+
   return function apiErrorHandler(err, req, res, next) {
     var status = err.status || err.statusCode || 500;
     if (status < 400) status = 500;
@@ -32,6 +34,12 @@ module.exports = function () {
     if (err.name) body.name = err.name;
     if (err.type) body.type = err.type;
 
+    if (options.exposeAdditionalProperties) {
+      for (var key in err) {
+        if (err.hasOwnProperty(key) && !(key in body)) body[key] = err[key]
+      }
+    }
+
     res.json(body);
   }
 }

test/test.js

@@ -51,4 +51,24 @@ describe('API Error Handler', function () {
       done();
     })
   })
+
+  it('exposeAdditionalProperties', function (done) {
+    var app = express();
+    app.use(function (req, res, next) {
+      next(error(401, { foobar: 123 }));
+    });
+    app.use(handler({ exposeAdditionalProperties: true }));
+
+    request(app.listen())
+    .get('/')
+    .expect(401)
+    .end(function (err, res) {
+      assert.ifError(err);
+
+      var body = res.body;
+      assert.equal(body.foobar, 123);
+      assert.equal(body.status, 401);
+      done();
+    })
+  })
 })