Added support for extending classes via convenience method and tests for property inheritance

lib/class.js

@@ -82,6 +82,7 @@ var extend = function()
     prop_copy( props, prototype );
 
     // set up the new class
+    attach_extend( new_class );
     new_class.prototype   = prototype;
     new_class.constructor = new_class;
 
@@ -103,7 +104,9 @@ exports.extend = function( base )
 }
 
 
-/**
+var attach_extend = function( func )
+{
+    /**
      * Shorthand for extending classes
      *
      * This method can be invoked on the object, rater than having to call
@@ -113,8 +116,8 @@ exports.extend = function( base )
      *
      * @return  {Object}  extended class
      */
-Object.defineProperty( Class, 'extend',
+    Object.defineProperty( func, 'extend',
-{
+    {
         value: function( props )
         {
             return extend( this, props );
@@ -123,5 +126,5 @@ Object.defineProperty( Class, 'extend',
         enumerable:   false,
         writable:     false,
         configurable: false,
-} );
+    } );
-
+}

test/test-class-extend.js

@@ -25,11 +25,44 @@ require( './common' );
 var assert = require( 'assert' ),
     Class  = require( 'class' );
 
-var Foo = Class.extend();
+var foo_props = {
-
+        one: 1,
+        two: 2,
+    },
+    Foo = Class.extend( foo_props );
 
 assert.ok(
-    ( Foo.prototype.extend instanceof Function ),
+    ( Foo.extend instanceof Function ),
-    "Created class contains extend method in prototype"
+    "Created class contains extend method"
 );
 
+var sub_props = {
+        three: 3,
+        four:  4,
+    },
+    SubFoo = Foo.extend( sub_props );
+
+assert.ok(
+    ( SubFoo instanceof Object ),
+    "Subtype is returned as an object"
+);
+
+// ensure properties were inherited from supertype
+for ( var prop in foo_props )
+{
+    assert.equal(
+        foo_props[ prop ],
+        SubFoo.prototype[ prop ],
+        "Subtype inherits parent properties: " + prop
+    );
+}
+
+// and ensure that the subtype's properties were included
+for ( var prop in sub_props )
+{
+    assert.equal(
+        sub_props[ prop ],
+        SubFoo.prototype[ prop ],
+        "Subtype contains its own properties: " + prop
+    );
+}