単純RingBuffer (JavaScript)

[JavaScript で色んなデータ構造（list/stack/queue/tree） http://c4se.hatenablog.com/entry/2012/01/28/190714 ]続き。単なるRingBufferとして、動的配列の用途には適しません。

/**
 * @fileOverView Simple RingBuffer class.
 * @author ne_Sachirou http://c4se.tk/profile/ne.html
 * @license 2012 Public Domain
 */

(function (global) {

if (!Object.keys) {
  Object.keys = function (obj) {
    var result = [],
        key,
        i = 0;

    for (key in obj) {
      if (obj.hasOwnProperty(key)) {
        result[i] = key;
        i += 1;
      }
    }
    return result;
  };
}


/**
 * @param {Object} target
 * @param {Object} source
 * @param {Boolean=false} does_overwrite
 */
function mixin (target, source, does_overwrite) {
  var keys = Object.keys(source),
      key,
      i = -1;

  while (key = keys[++i]) {
    if (does_overwrite || target[key] === void 0) {
      target[key] = source[key];
    }
  }
}


mixin(global, {
  RingBuffer: RingBuffer,
});

mixin(RingBuffer.prototype, {
  index: RingBuffer_index,
  forEach: RingBuffer_forEach
});


/**
 * @class
 * Use reminder operator.
 * @param {Number=Ringbuffer1.INITIAL_SIZE} size
 * @property {Number} size
 */
function RingBuffer (size) {
  if (!(this instanceof RingBuffer)) {return new RingBuffer(size);}
  this.size = size || RingBuffer.INITIAL_SIZE;
  this.datas = new Array(this.size);
}


/**@constant*/
RingBuffer.INITIAL_SIZE = Math.pow(2, 8);


/**
 * @param {Number} num
 * @return {Object}
 */
function RingBuffer_getIndex (num) {
  return this.datas[num % this.size];
}


/**
 * @param {Number} num
 * @param {Object} data
 * @return {RingBuffer} this
 */
function RingBuffer_setIndex (num, data) {
  this.datas[num % this.size] = data;
  return this;
}


/**
 * Wrapper method of getIndex and setIndex.
 * @param {Number} num
 * @param {Object=undefined} data
 * @return {Object|RingBuffer}
 */
function RingBuffer_index (num, data) {
  console.log(this);
  if (data === void 0) {
    return RingBuffer_getIndex.call(this, num);
  } else {
    return RingBuffer_setIndex.call(this, num, data);
  }
}


/**
 * Enumrator
 * @param {Function} fun
 *   fun(data, idx, this)
 * @param {Object} obj this in fun.
 * @return {Ringbuffer1} this
 */
function RingBuffer_forEach (fun, obj) {
  var datas = this.datas,
      data,
      i = -1;

  while (data = datas[++i]) {
    if (i in datas) {
      fun.call(obj, data, i, this);
    }
  }
  return this;
}

}(this));