Refactor Heaps.

Author: trekhleb

src/data-structures/heap/Heap.js

@@ -1,15 +1,18 @@
 import Comparator from '../../utils/comparator/Comparator';
 
 /**
- * Parent class for heaps
- * @class
+ * Parent class for Min and Max Heaps.
  */
-class Heap {
+export default class Heap {
   /**
    * @constructs Heap
    * @param {Function} [comparatorFunction]
    */
   constructor(comparatorFunction) {
+    if (new.target === Heap) {
+      throw new TypeError('Cannot construct Heap instance directly');
+    }
+
     // Array representation of the heap.
     this.heapContainer = [];
     this.compare = new Comparator(comparatorFunction);
@@ -131,7 +134,7 @@ class Heap {
 
   /**
    * @param {*} item
-   * @return {MinHeap}
+   * @return {Heap}
    */
   add(item) {
     this.heapContainer.push(item);
@@ -170,6 +173,12 @@ class Heap {
   toString() {
     return this.heapContainer.toString();
   }
-}
 
-export default Heap;
+  heapifyUp() {
+    throw new Error('You have to implement this method!');
+  }
+
+  heapifyDown() {
+    throw new Error('You have to implement this method!');
+  }
+}

src/data-structures/heap/MaxHeap.js

@@ -1,11 +1,6 @@
 import Heap from './Heap';
 
-/**
- * Creates a new MaxHeap
- * @class
- * @augments Heap
- */
-class MaxHeap extends Heap {
+export default class MaxHeap extends Heap {
   /**
    * @param {*} item
    * @param {Comparator} [customFindingComparator]
@@ -74,7 +69,7 @@ class MaxHeap extends Heap {
    * @param {number} [customStartIndex]
    */
   heapifyDown(customStartIndex) {
-    // Compare the root element to its children and swap root with the smallest
+    // Compare the root element to its children and swap root with the biggest
     // of children. Do the same for next children after swap.
     let currentIndex = customStartIndex || 0;
     let nextIndex = null;
@@ -100,5 +95,3 @@ class MaxHeap extends Heap {
     }
   }
 }
-
-export default MaxHeap;

src/data-structures/heap/MinHeap.js

@@ -1,11 +1,6 @@
 import Heap from './Heap';
 
-/**
- * Creates a new MinHeap
- * @class
- * @augments Heap
- */
-class MinHeap extends Heap {
+export default class MinHeap extends Heap {
   /**
    * @param {*} item
    * @param {Comparator} [customFindingComparator]
@@ -98,5 +93,3 @@ class MinHeap extends Heap {
     }
   }
 }
-
-export default MinHeap;

src/data-structures/heap/__test__/Heap.test.js

@@ -0,0 +1,12 @@
+import Heap from '../Heap';
+
+describe('Heap', () => {
+  it('should not allow to create instance of the Heap directly', () => {
+    const instantiateHeap = () => {
+      const heap = new Heap();
+      heap.add(5);
+    };
+
+    expect(instantiateHeap).toThrow();
+  });
+});