--update: added linked list

Author: ashokdey

src/_DataStructures_/LinkedList/LinkedList.test.js

@@ -0,0 +1,51 @@
+const { Node, LinkedList } = require('.');
+
+describe('Data Structures: Linked Lists', () => {
+  describe('Node of a List', () => {
+    it('Should be a class', () => {
+      expect(typeof Node.prototype.constructor).toEqual('function');
+    });
+
+    it('Should set the data and next field of a node', () => {
+      const node = new Node('Hello', null);
+      expect(node.data).toEqual('Hello');
+      expect(node.next).toEqual(null);
+    });
+  });
+
+  describe('LinkedList Instance', () => {
+    it('Should be a class', () => {
+      expect(typeof LinkedList.prototype.constructor).toEqual('function');
+    });
+
+    it('Should set the data and next field of a node', () => {
+      const list = new LinkedList();
+      expect(list.head).not.toEqual(undefined);
+      expect(list.head).toEqual(null);
+    });
+  });
+
+  describe('LinkedList API', () => {
+    let list = new LinkedList();
+
+    beforeEach(() => {
+      list = new LinkedList();
+    });
+
+    it('Should add element at beginning using list.addAtBeginning()', () => {
+      list.addAtBeginning(12);
+      expect(list.head.data).toEqual(12);
+
+      list.addAtBeginning(15);
+      expect(list.head.data).toEqual(15);
+    });
+
+    it('Should return the present size of the list using list.length()', () => {
+      expect(list.length()).toEqual(0);
+      list.addAtBeginning(1);
+      list.addAtBeginning(2);
+      list.addAtBeginning(3);
+      expect(list.length()).toEqual(3);
+    });
+  });
+});

src/_DataStructures_/LinkedList/index.js

@@ -0,0 +1,35 @@
+class Node {
+  constructor(data, next) {
+    this.data = data;
+    this.next = next;
+  }
+}
+
+class LinkedList {
+  constructor() {
+    this.head = null;
+  }
+
+  addAtBeginning(element) {
+    const node = new Node(element, null);
+
+    if (!this.head) {
+      this.head = node;
+    } else {
+      node.next = this.head;
+      this.head = node;
+    }
+  }
+
+  length() {
+    let address = this.head;
+    let count = 0;
+    while (address) {
+      count += 1;
+      address = address.next;
+    }
+    return count;
+  }
+}
+
+module.exports = { LinkedList, Node };