CircularBuffer.js

'use strict'

// Circular buffer storage. Externally-apparent 'length' increases indefinitely
// while any items with indexes below length-n will be forgotten (undefined
// will be returned if you try to get them, trying to set is an exception).
// n represents the initial length of the array, not a maximum
function CircularBuffer (n) {
  this._array = new Array(n)
  this.length = 0 
  this.size = n 
}
CircularBuffer.prototype.toString = function () {
  return '[object CircularBuffer(' + this._array.length + ') length ' + this.length + ']' 
}
CircularBuffer.prototype.get = function (i) {
  if (i < 0 || i < this.length - this._array.length) { return undefined }
  return this._array[i % this._array.length]
}
CircularBuffer.prototype.push = function (v) {
  this._array[this.length % this._array.length] = v 
  this.length++
}
CircularBuffer.prototype.set = function (i, v) {
  if (i < 0 || i < this.length - this._array.length) { throw CircularBuffer.IndexError }
  while (i > this.length) {
    this._array[this.length % this._array.length] = undefined
    this.length++
  }
  this._array[i % this._array.length] = v 
  if (i === this.length) { this.length++ }
}
CircularBuffer.IndexError = {}