fix: support extending an ES2015 class

Only if `Reflect.construct` is available.

Fixes #18

Author: julien-f

.travis.yml

@@ -1,6 +1,7 @@
 language: node_js
 node_js:
   - stable
+  - 8
   - 6
   - 5
   - 4

index.js

@@ -4,6 +4,7 @@
 
 // ===================================================================
 
+var construct = typeof Reflect !== 'undefined' ? Reflect.construct : undefined
 var defineProperty = Object.defineProperty
 
 // -------------------------------------------------------------------
@@ -102,7 +103,9 @@ function makeError (constructor, super_) {
   var name
   if (typeof constructor === 'string') {
     name = constructor
-    constructor = function () { super_.apply(this, arguments) }
+    constructor = construct !== undefined
+      ? function () { return construct(super_, arguments, constructor) }
+      : function () { super_.apply(this, arguments) }
 
     // If the name can be set, do it once and for all.
     if (setFunctionName !== undefined) {

index.spec.js

@@ -169,4 +169,20 @@ describe('BaseError', function () {
     expect(typeof e.stack).toBe('string')
     compareStacks(e.stack, stack)
   })
+
+  ;(typeof Reflect !== 'undefined' ? it : it.skip)('can be reused as base error', function () {
+    class MyBaseError extends BaseError {}
+    var MyError = makeError('MyError', MyBaseError)
+
+    var e = new MyError('my error message'); var stack = new Error().stack
+
+    expect(e).toBeInstanceOf(Error)
+    expect(e).toBeInstanceOf(BaseError)
+    expect(e).toBeInstanceOf(MyError)
+
+    expect(e.name).toBe('MyError')
+    expect(e.message).toBe('my error message')
+    expect(typeof e.stack).toBe('string')
+    compareStacks(e.stack, stack)
+  })
 })

package.json

@@ -32,6 +32,9 @@
     "standard": "^10.0.3",
     "uglify-js": "^3.3.2"
   },
+  "jest": {
+    "testEnvironment": "node"
+  },
   "scripts": {
     "commitmsg": "yarn test",
     "dev-test": "jest --watch",