util: make inherits work with classes

The current implementation overwrites the prototype of the target
constructor. It is not allowed with ES2015 classes because the prototype
property is read only. Use Object.setPrototypeOf instead.

Fixes: #3452
PR-URL: #3455
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: targos

lib/util.js

@@ -761,14 +761,7 @@ exports.inherits = function(ctor, superCtor) {
                         'have a prototype.');
 
   ctor.super_ = superCtor;
-  ctor.prototype = Object.create(superCtor.prototype, {
-    constructor: {
-      value: ctor,
-      enumerable: false,
-      writable: true,
-      configurable: true
-    }
-  });
+  Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
 };
 
 exports._extend = function(origin, add) {

test/parallel/test-util-inherits.js

@@ -40,6 +40,40 @@ const c = new C();
 assert.strictEqual(c.getValue(), 'abc');
 assert.strictEqual(c.constructor, C);
 
+// inherits can be called after setting prototype properties
+function D() {
+  C.call(this);
+  this._d = 'd';
+}
+
+D.prototype.d = function() { return this._d; };
+inherits(D, C);
+
+assert.strictEqual(D.super_, C);
+
+const d = new D();
+assert.strictEqual(d.c(), 'c');
+assert.strictEqual(d.d(), 'd');
+assert.strictEqual(d.constructor, D);
+
+// ES6 classes can inherit from a constructor function
+class E {
+  constructor() {
+    D.call(this);
+    this._e = 'e';
+  }
+  e() { return this._e; }
+}
+inherits(E, D);
+
+assert.strictEqual(E.super_, D);
+
+const e = new E();
+assert.strictEqual(e.getValue(), 'abc');
+assert.strictEqual(e.d(), 'd');
+assert.strictEqual(e.e(), 'e');
+assert.strictEqual(e.constructor, E);
+
 // should throw with invalid arguments
 assert.throws(function() { inherits(A, {}); }, TypeError);
 assert.throws(function() { inherits(A, null); }, TypeError);