Added Doubly Linked List DS example

.gitignore

@@ -0,0 +1 @@
+node_modules

package.json

@@ -24,6 +24,8 @@
   },
   "homepage": "https://github.com/nas5w/javascript-patterns#readme",
   "dependencies": {
+    "chalk": "^2.4.2",
+    "cli-table2": "^0.2.0",
     "husky": "^1.3.1",
     "jest": "^24.7.1"
   },

src/dataStructures/doublyLinkedList.js

@@ -0,0 +1,245 @@
+const Table = require('cli-table2');
+const chalk = require('chalk');
+
+class Node {
+    constructor(data) {
+        this.data = data;
+        this.next = null;
+        this.prev = null;
+    }
+}
+
+class DoublyLinkedList {
+    constructor() {
+        this.head = null;
+        this.tail = null;
+    }
+
+    append(item) {
+        let node = new Node(item);
+
+        if (!this.head) {
+            this.head = node;
+            this.tail = node;
+        } else {
+            node.prev = this.tail;
+            this.tail.next = node;
+            this.tail = node
+        }
+    }
+
+    appendAt(pos, item) {
+        let current = this.head;
+        let counter = 1;
+        let node = new Node(item);
+        if (pos == 0) {
+            this.head.prev = node
+            node.next = this.head
+            this.head = node
+        } else {
+            while (current) {
+                current = current.next;
+                if (counter == pos) {
+                    node.prev = current.prev
+                    current.prev.next = node
+                    node.next = current
+                    current.prev = node
+                }
+                counter++
+            }
+        }
+    }
+
+    appendAfter(item) {
+        // 
+    }
+
+    remove(item) {
+        let current = this.head;
+        while (current) {
+            if (current.data === item) {
+                if (current == this.head && current == this.tail) {
+                    this.head = null;
+                    this.tail = null;
+                } else if (current == this.head) {
+                    this.head = this.head.next
+                    this.head.prev = null
+                } else if (current == this.tail) {
+                    this.tail = this.tail.prev;
+                    this.tail.next = null;
+                } else {
+                    current.prev.next = current.next;
+                    current.next.prev = current.prev;
+                }
+            }
+            current = current.next
+        }
+    }
+
+    removeAt(pos) {
+        let current = this.head;
+        let counter = 1;
+        if (pos == 0) {
+            this.head = this.head.next;
+            this.head.prev = null;
+        } else {
+            while (current) {
+                current = current.next
+                if (current == this.tail) {
+                    this.tail = this.tail.prev;
+                    this.tail.next = null;
+                } else if (counter == pos) {
+                    current.prev.next = current.next;
+                    current.next.prev = current.prev;
+                    break;
+                }
+                counter++;
+            }
+        }
+    }
+
+    reverse() {
+        let current = this.head;
+        let prev = null;
+        while (current) {
+            let next = current.next
+            current.next = prev
+            current.prev = next
+            prev = current
+            current = next
+        }
+        this.tail = this.head
+        this.head = prev
+    }
+
+    swap(nodeOne, nodeTwo) {
+        let current = this.head;
+        let counter = 0;
+        let firstNode;
+
+        // Make sure we are okay to go
+        if (nodeOne === nodeTwo) {
+            console.log("ERROR: 'SWAP' both the nodes must be different!");
+            return false;
+        } else if (nodeOne > nodeTwo) {
+            let temp = nodeOne;
+            nodeOne = nodeTwo;
+            nodeTwo = temp;
+        }
+
+        if (nodeOne < 0 || nodeTwo < 0) {
+            console.log("ERROR: 'SWAP' both the nodes must be index & index can not be negative!");
+            return false;
+        }
+
+        // Swap nodes
+        while (current !== null) {
+            if (counter == nodeOne) {
+                firstNode = current;
+            } else if (counter == nodeTwo) {
+                let temp = current.data;
+                current.data = firstNode.data;
+                firstNode.data = temp;
+            }
+            current = current.next;
+            counter++;
+        }
+        return true
+    }
+
+    length() {
+        let current = this.head;
+        let counter = 0;
+        while (current !== null) {
+            counter++
+            current = current.next
+        }
+        return counter;
+    }
+
+    display() {
+        let current = this.head;
+        let elements = [];
+        while (current !== null) {
+            elements.push(current.data);
+            current = current.next
+        }
+        return elements.join(" ");
+    }
+
+    isEmpty() {
+        return this.length() < 1
+    }
+
+    traverse(fn) {
+        if (!fn || typeof fn !== 'function') {
+            console.log("ERROR: 'TRAVERSE' function is undefined!");
+            return false;
+        }
+        let current = this.head;
+        while (current !== null) {
+            fn(current)
+            current = current.next;
+        }
+        return true;
+    }
+
+    traverseReverse(fn) {
+        if (!fn || typeof fn !== 'function') {
+            console.log("ERROR: 'TRAVERSE_REVERSE' function is undefined!");
+            return false;
+        }
+        let current = this.tail;
+        while (current !== null) {
+            fn(current)
+            current = current.prev;
+        }
+        return true;
+    }
+
+    search(item) {
+        let current = this.head;
+        let counter = 0;
+
+        while (current) {
+            if (current.data == item) {
+                return counter
+            }
+            current = current.next
+            counter++
+        }
+        return false;
+    }
+
+	/* 
+	* 	EXTRA 
+	*/
+    prettyPrint() {
+        let current = this.head;
+        let output = [chalk.red('Head') + ' ->'];
+        while (current !== null) {
+            output.push(chalk.cyan(current.data));
+            current = current.next;
+        }
+        output.push('<- ' + chalk.red('Tail'));
+        this.table(output);
+        return true;
+    }	// </ PrettyPrint>
+
+    table(output) {
+        let table = new Table({
+            chars: {
+                'top': '─', 'top-mid': '╤', 'top-left': '╔', 'top-right': '╗'
+                , 'bottom': '─', 'bottom-mid': '╧', 'bottom-left': '╚', 'bottom-right': '╝'
+                , 'left': '│', 'left-mid': '╟', 'mid': '─', 'mid-mid': '┼'
+                , 'right': '│', 'right-mid': '╢', 'middle': '│'
+            },
+            style: { border: ['yellow'] }
+        });
+        table.push(output);
+        console.log(table.toString());
+        return true
+    } // </ Table>
+}
+
+module.exports = DoublyLinkedList