Made notes on circular references.

Author: selsamman

test/circular.ts

@@ -1,8 +1,30 @@
 import {expect} from 'chai';
-import {Fruit} from './circular/fruit';
+
+import {Basket} from "./circular/basket";
 import {Peach} from './circular/peach';
 import {Pear} from './circular/pear';
-import {Basket} from "./circular/basket";
+import {Fruit} from './circular/fruit';
+
+/***
+ * Circular referencese
+ *
+ * You will get a run-time error "Object prototype may only be an Object or null: undefined at line 7 of peach.js" if your
+ * imports are such that Fruit is imported first as in ....
+ import {Fruit} from './circular/fruit';
+ import {Peach} from './circular/peach';
+ import {Pear} from './circular/pear';
+ import {Basket} from "./circular/basket";
+ *
+ * This is because the order or processing will be:
+ * 1) Fruit is invoked. Fruit imports basket.
+ * 2) Basket then imports Peach and Pear
+ * 3) Peach and Pear then import Fruit (which is already in process of being imported and so undefined is returned)
+ * 4) Since Peach extends Fruit and Fruit is undefined an incorrect class is generated
+ * 5) When an instance Fruit is created it fails
+ *
+ * However by importing Basket first, Basket and Fruit are ready by the time the extends comes along
+ *
+ */
 
 describe('Create fruit', () => {
     it('Can identify types of fruit', () => {

test/circular/fruit.ts

@@ -2,6 +2,6 @@ import {Basket} from "./basket";
 export class Fruit {
     basket: Basket;
     addNewBasket () {
-        //this.basket = new Basket();
+        this.basket = new Basket();
     }
 }