support for custom prototypes for creating families

lib/makeerror.js

@@ -26,12 +26,18 @@ module.exports = makeError
  * @param Object  The default data object, merged with per instance data.
  */
 function makeError(name, defaultMessage, defaultData) {
+  defaultMessage = defaultMessage || ''
+  defaultData = defaultData || {}
+
   var CustomError = function(message, data) {
     if (!(this instanceof CustomError)) return new CustomError(message, data)
     this.name = name
-    this.message = message || defaultMessage || ''
-    this.data = data || defaultData || {}
+    this.message = message || defaultMessage
+    this.data = data || defaultData
   }
-  CustomError.prototype = new Error()
+
+  CustomError.prototype = defaultData.proto || new Error()
+  delete defaultData.proto
+
   return CustomError
 }

package.json

@@ -1,7 +1,7 @@
 {
   "name": "makeerror",
   "description": "A library to make errors.",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "author": "Naitik Shah <n@daaku.org>",
   "main": "lib/makeerror",
   "repository": {

test/makeerror-tests.js

@@ -67,3 +67,36 @@ exports['different but the same'] = function(beforeExit) {
   assert.ok(er2 instanceof MyError2, 'Must be an instance of MyError2')
   assert.ok(!(er2 instanceof MyError1), 'Must not be an instance of MyError1')
 }
+
+exports['custom prototype'] = function(beforeExit) {
+  var parentName = 'ParentError'
+    , ParentError = makeError(parentName)
+    , childName = 'ChildError'
+    , ChildError = makeError(childName, '', { proto: ParentError() })
+    , parentEr = ParentError()
+    , childEr = ChildError()
+
+  assert.strictEqual(parentEr.name, parentName, 'expect parentName')
+  assert.ok(parentEr instanceof ParentError, 'expect instanceof ParentError')
+  assert.ok(parentEr instanceof Error, 'expect instanceof Error')
+  assert.ok(!(parentEr instanceof ChildError), 'not an instanceof ChildError')
+
+  assert.strictEqual(childEr.name, childName, 'expect childName')
+  assert.ok(childEr instanceof ChildError, 'expect instanceof ChildError')
+  assert.ok(childEr instanceof ParentError, 'expect instanceof ParentError')
+  assert.ok(childEr instanceof Error, 'expect instanceof Error')
+}
+
+exports['custom prototype two levels'] = function(beforeExit) {
+  var GParentError = makeError('GParentError')
+    , ParentError = makeError('ParentError', '', { proto: GParentError() })
+    , childName = 'ChildError'
+    , ChildError = makeError(childName, '', { proto: ParentError() })
+    , childEr = ChildError()
+
+  assert.strictEqual(childEr.name, childName, 'expect childName')
+  assert.ok(childEr instanceof ChildError, 'expect instanceof ChildError')
+  assert.ok(childEr instanceof ParentError, 'expect instanceof ParentError')
+  assert.ok(childEr instanceof GParentError, 'expect instanceof GParentError')
+  assert.ok(childEr instanceof Error, 'expect instanceof Error')
+}