JS double linked list

JavaScript/Double Linked List/index.js

@@ -0,0 +1,148 @@
+function DoublyLinkedList() {
+  var Node = function (element) {
+    this.element = element;
+    this.next = null;
+    this.prev = null;
+  };
+
+  var length = 0;
+  var head = null;
+  var tail = null;
+
+  this.append = function (element) {
+    var node = new Node(element),
+      current;
+
+    if (head === null) {
+      head = node;
+      tail = node;
+    } else {
+      current = head;
+
+      while (current.next) {
+        current = current.next;
+      }
+      current.next = node;
+      tail = node;
+    }
+    length++;
+  };
+
+  this.insert = function (position, element) {
+    if (position >= 0 && position <= length) {
+      var node = new Node(element),
+        current = head,
+        previous,
+        index = 0;
+
+      if (position === 0) {
+        if (!head) {
+          head = node;
+          tail = node;
+        } else {
+          node.next = current;
+          current.prev = node;
+          head = node;
+        }
+      } else if (position === length) {
+        current = tail;
+        current.next = node;
+        node.prev = current;
+        tail = node;
+      } else {
+        while (index++ < position) {
+          previous = current;
+          current = current.next;
+        }
+        node.next = current;
+        previous.next = node;
+        current.prev = node;
+        node.prev = previous;
+      }
+      length++;
+      return true;
+    } else {
+      return false;
+    }
+  };
+
+  this.removeAt = function (position) {
+    if (position > -1 && position < length) {
+      var current = head,
+        previous,
+        index = 0;
+
+      if (position === 0) {
+        head = current.next;
+
+        if (length === 1) {
+          tail = null;
+        } else {
+          head.prev = null;
+        }
+      } else if (position === length - 1) {
+        current = tail;
+        tail = current.prev;
+        tail.next = null;
+      } else {
+        while (index++ < position) {
+          previous = current;
+          current = current.next;
+        }
+        previous.next = current.next;
+        current.next.prev = previous;
+      }
+      length--;
+      return current.element;
+    } else {
+      return null;
+    }
+  };
+
+  this.remove = function (element) {
+    var index = this.indexOf(element);
+    return this.removeAt(index);
+  };
+
+  this.indexOf = function (element) {
+    var current = head,
+      index = 0;
+
+    while (current) {
+      if (element === current.element) {
+        return index;
+      }
+      index++;
+      current = current.next;
+    }
+    return -1;
+  };
+
+  this.isEmpty = function () {
+    return length === 0;
+  };
+
+  this.size = function () {
+    return length;
+  };
+
+  this.getHead = function () {
+    return head;
+  };
+
+  this.toString = function () {
+    var current = head,
+      string = '';
+
+    while (current) {
+      string += current.element + ' ';
+      current = current.next;
+    }
+
+    return string;
+  };
+
+  this.print = function () {
+    console.log(this.toString());
+  };
+}