wal/build/queue.js

An implementation of write-ahead logging (WAL) for nodejs.

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});

var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

var $queue = Symbol('queue');
var $offset = Symbol('offset');

/**
 * A simple queue class.
 *
 * This is an obvious es6 dirivative of [Stephen Morley's queue implementation](http://code.stephenmorley.org/javascript/queues/).
 */

var Queue = function () {

  /**
   * Creates a new instance.
   */

  function Queue() {
    _classCallCheck(this, Queue);

    this[$queue] = [];
    this[$offset] = 0;
  }

  /**
   * @type {number} The queue's length.
   */


  _createClass(Queue, [{
    key: 'enqueue',


    /**
     * Enqueues the specified item.
     * @param item - An item to put on the queue.
     */
    value: function enqueue(item) {
      this[$queue].push(item);
    }

    /**
     * Dequeues the item at the head of the queue, removing the item.
     * @return The item at the head of the queue or `undefined` if the queue is empty.
     */

  }, {
    key: 'dequeue',
    value: function dequeue() {
      if (this.length === 0) {
        return undefined;
      }
      var item = this[$queue][this[$offset]];
      if (++this[$offset] * 2 >= this[$queue].length) {
        this[$queue] = this[$queue].slice(this[$offset]);
        this[$offset] = 0;
      }
      return item;
    }

    /**
     * Peeks at the item at the head of the queue without removing it.
     * @return The item at the head of the queue or `undefined` if the queue is empty.
     */

  }, {
    key: 'peek',
    value: function peek() {
      return this.length > 0 ? this[$queue][this[$offset]] : undefined;
    }
  }, {
    key: 'length',
    get: function get() {
      return this[$queue].length - this[$offset];
    }

    /**
     * @type {boolean} Indicates whether the queue is empty.
     */

  }, {
    key: 'isEmpty',
    get: function get() {
      return this.length === 0;
    }
  }]);

  return Queue;
}();

exports.default = Queue;
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