dequeue

A Simple Double Ended Queue Datastructure

Dequeue is implemented as a doubly linked circular list with a titular head node. By "titular head node", I mean an empty node to designate the beginning and end of the circularly linked list. I first saw this construction in the linux kernel source and it seem simple and elegant. I added the .length property to use it like I was using an Array.

I was using a javascript Array as a FIFO. Somewhere between 100,000 and 200,000 entries the program performance went to hell (dev host is a MBP w/8GB RAM). 15 minutes later, I implemented a simple dequeue and my FIFO scales up to millions of entries.

It is a drop-in replacement for javascript-arrays-as-fifo.

Example: Dequeue as a replacement for an Array as a FIFO

var Dequeue = require('dequeue')

//var fifo = []
var fifo = new Dequeue()

fifo.length === 0 //=> true

fifo.push(d1)
fifo.length === 1 //=> true

fifo.unshift(d2)

fifo.pop() === d1 //=> true

fifo.push(d3)

fifo.shift() === d2 //=> true

fifo.length === 1 //=> true; only d3 is in the dequeue

API

deque = new Dequeue()

deque.push(value)

Push a value on the end.

value = deque.pop()

Remove a value off the end.

deque.unshift(value)

Push a value on the beginning.

value = deque.shift()

Remove a value off the beginning.

value = deque.last()

Examine the value of the end without removing it.

value = deque.first()

Examine the value of the beginning without removing it.

deque.empty()

Remove all entries. This is NOT a test for an empty dequeue; use deque.length for that.

Future Development

Something this simple does not really need a roadmap. However, I am thinking of adding APIs to facilitate walking the Linked List via an iterator. It will be simple and fully backward compatible.

About the Code

I was convinced by a blog posting by Issac Z. Schlueter that I don't need semicolons. So I don't use them.