fix(extend): super_ should be available for backwards compatibility (#…

…6329)

Fixes #6328

src/js/extend.js

@@ -44,6 +44,11 @@ const extend = function(superClass, subClassMethods = {}) {
 
   _inherits(subClass, superClass);
 
+  // this is needed for backward-compatibility and node compatibility.
+  if (superClass) {
+    subClass.super_ = superClass;
+  }
+
   // Extend subObj's prototype with functions and other properties from props
   for (const name in methods) {
     if (methods.hasOwnProperty(name)) {

test/unit/extend.test.js

@@ -16,3 +16,15 @@ QUnit.test('should add implicit parent constructor call', function(assert) {
   assert.ok(superCalled, 'super constructor called');
   assert.ok(child.foo, 'child properties set');
 });
+
+QUnit.test('should have a super_ pointer', function(assert) {
+  const Parent = function() {};
+  const Child = extend(Parent, {
+    foo: 'bar'
+  });
+
+  const child = new Child();
+
+  assert.ok(child.foo, 'child properties set');
+  assert.equal(child.constructor.super_, Parent, 'super_ is present and equal to the super class');
+});