JavaScript DoublyLinkedList

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.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.previous = 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

}

}

}