added about_prototype_chain

Author: saitodisse

jskoans.htm

@@ -17,6 +17,7 @@
   <script type="text/javascript" src="topics/about_objects.js"></script>
   <script type="text/javascript" src="topics/about_arrays.js"></script>
   <script type="text/javascript" src="topics/about_reflection.js"></script>
+  <script type="text/javascript" src="topics/about_prototype_chain.js"></script>
   <script type="text/javascript" src="topics/about_prototypal_inheritance.js"></script>
   <script type="text/javascript" src="topics/about_functions_and_closure.js"></script>
   <script type="text/javascript" src="topics/about_this.js"></script>

topics/about_prototype_chain.js

@@ -0,0 +1,58 @@
+// demonstrate objects prototype chain
+
+// https://developer.mozilla.org/en/JavaScript/Guide/Inheritance_and_the_prototype_chain
+module("About Prototype Chain (topics/about_prototype_chain.js)");
+
+var father = {
+  b: 3,
+  c: 4
+};
+
+var child = Object.create(father);
+child.a = 1;
+child.b = 2;
+
+/*
+ * ---------------------- ---- ---- ----
+ *                      [a]  [b]  [c]
+ * ---------------------- ---- ---- ----
+ * [child]               1    2
+ * ---------------------- ---- ---- ----
+ * [father]                   3    4
+ * ---------------------- ---- ---- ----
+ * [Object.prototype]
+ * ---------------------- ---- ---- ----
+ * [null]
+ * ---------------------- ---- ---- ----
+ * */
+
+test("Is there an 'a' and 'b' own property on childObj?", function () {
+  equals(child.a, __, 'what is \'a\' value?');
+  equals(child.b, __, 'what is \'b\' value?');
+});
+
+test("If 'b' was removed, whats b value?", function () {
+  delete child.b;
+  equals(child.b, __, 'what is \'b\' value now?');
+});
+
+
+// Is there a 'c' own property on childObj? No, check its prototype
+// Is there a 'c' own property on childObj.[[Prototype]]? Yes, its value is...
+test("Is there a 'c' own property on childObj.[[Prototype]]?", function () {
+  equals(child.hasOwnProperty('c'), __, 'childObj.hasOwnProperty(\'c\')?');
+});
+
+test("Is there a 'c' own property on childObj.[[Prototype]]?", function () {
+  equals(child.c, __, 'childObj.c?');
+});
+
+
+// Is there a 'd' own property on childObj? No, check its prototype
+// Is there a 'd' own property on childObj.[[Prototype]]? No, check it prototype
+// childObj.[[Prototype]].[[Prototype]] is null, stop searching, no property found, return...
+test("Is there an 'd' own property on childObj?", function () {
+  equals(child.d, __, 'what is the value of childObj.d?');
+});
+
+