webpack/lib/util/ArrayQueue.js

Packs ECMAScript/CommonJs/AMD modules for the browser. Allows you to split your codebase into multiple bundles, which can be loaded on demand. Supports 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";

/**
 * FIFO queue backed by arrays with a reversed dequeue buffer to avoid the cost
 * of repeated `Array#shift` operations.
 * @template T
 */
class ArrayQueue {
	/**
	 * Seeds the queue with an optional iterable of items in dequeue order.
	 * @param {Iterable<T>=} items The initial elements.
	 */
	constructor(items) {
		/**
		 * @private
		 * @type {T[]}
		 */
		this._list = items ? [...items] : [];
		/**
		 * @private
		 * @type {T[]}
		 */
		this._listReversed = [];
	}

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

	/**
	 * Removes all pending items from both internal buffers.
	 */
	clear() {
		this._list.length = 0;
		this._listReversed.length = 0;
	}

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

	/**
	 * Removes and returns the next item in FIFO order, switching to a reversed
	 * buffer when that is cheaper than shifting from the front of the array.
	 * @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;
			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();
	}

	/**
	 * Removes the first matching item from whichever internal buffer currently
	 * contains it.
	 * @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]() {
		return {
			next: () => {
				const item = this.dequeue();
				if (item) {
					return {
						done: false,
						value: item
					};
				}
				return {
					done: true,
					value: undefined
				};
			}
		};
	}
}

module.exports = ArrayQueue;