webpack/lib/util/ArrayQueue.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

/**
 * @template T
 */
class ArrayQueue {
	/**
	 * @param {Iterable<T>=} items The initial elements.
	 */
	constructor(items) {
		/** @private @type {T[]} */
		this._list = items ? Array.from(items) : [];
		/** @private @type {T[]} */
		this._listReversed = [];
	}

	/**
	 * Returns the number of elements in this queue.
	 * @returns {number} The number of elements in this queue.
	 */
	get length() {
		return this._list.length + this._listReversed.length;
	}

	/**
	 * Empties the queue.
	 */
	clear() {
		this._list.length = 0;
		this._listReversed.length = 0;
	}

	/**
	 * Appends the specified element to this queue.
	 * @param {T} item The element to add.
	 * @returns {void}
	 */
	enqueue(item) {
		this._list.push(item);
	}

	/**
	 * Retrieves and removes the head of this queue.
	 * @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
	 */
	dequeue() {
		if (this._listReversed.length === 0) {
			if (this._list.length === 0) return undefined;
			if (this._list.length === 1) return this._list.pop();
			if (this._list.length < 16) return this._list.shift();
			const temp = this._listReversed;
			this._listReversed = this._list;
			this._listReversed.reverse();
			this._list = temp;
		}
		return this._listReversed.pop();
	}

	/**
	 * Finds and removes an item
	 * @param {T} item the item
	 * @returns {void}
	 */
	delete(item) {
		const i = this._list.indexOf(item);
		if (i >= 0) {
			this._list.splice(i, 1);
		} else {
			const i = this._listReversed.indexOf(item);
			if (i >= 0) this._listReversed.splice(i, 1);
		}
	}

	[Symbol.iterator]() {
		let i = -1;
		let reversed = false;
		return {
			next: () => {
				if (!reversed) {
					i++;
					if (i < this._list.length) {
						return {
							done: false,
							value: this._list[i]
						};
					}
					reversed = true;
					i = this._listReversed.length;
				}
				i--;
				if (i < 0) {
					return {
						done: true,
						value: undefined
					};
				}
				return {
					done: false,
					value: this._listReversed[i]
				};
			}
		};
	}
}

module.exports = ArrayQueue;