queue
=====

Two-array implementation of queue (.push, .shift) for JavaScript

Originally created as a simple fast queue implementation
around 2010 in one of @creationix repos (nStore, maybe)
where implementation sucked because of `.shift()` being slow.

This repo only contains the `Queue` class itself,
written as traditional (`new`-able) JavaScript class,
and fixing `.push` to be able to take variable number of arguments.

How to install
---

The `Queue` class is available in both npm and bower,
usable as either node.js module, AMD module or global in the browser.
You can install it with either of:

    npm install hqueue

    bower install hqueue

The idea
----

The idea behind this queue is to avoid `shift` call.
This is accomplished by increasing the read index in an array
and returning the element at that index.
If using single array, this would fill the memory with ever-growing
array. So two arrays are used - the read array is only used to read
the front element by increasing the read index as told above.
The second array is used to append new elements at the back.
When the read array is exhausted, the write array
becomes the read array, and empty write array is used to continue writing.

As implementation of array `.push` tends to be _O(n)_ in average,
and so should be the `Queue`. Moveover, exhausted read array is just
shortened (`.length = 0`) and reused as write array,
to allow to reuse already allocated capacity
to make appending _O(1)_ most of the times.

API
----
Reuses small subset of `Array` API so as to allow direct replacement of an array:

  - `.shift()` remove and return front element or `undefined`
  - `.push(...args)` append `...args` at the back of the queue
  - `.length` return number of elements in the queue