webpack/lib/util/Queue.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 that keeps items unique by storing them in insertion order inside
 * a `Set`.
 * @template T
 */
class Queue {
	/**
	 * Seeds the queue with an optional iterable of initial unique items.
	 * @param {Iterable<T>=} items The initial elements.
	 */
	constructor(items) {
		/**
		 * @private
		 * @type {Set<T>}
		 */
		this._set = new Set(items);
	}

	/**
	 * Returns the number of unique items currently waiting in the queue.
	 * @returns {number} The number of elements in this queue.
	 */
	get length() {
		return this._set.size;
	}

	/**
	 * Enqueues an item, moving nothing if that value is already present.
	 * @param {T} item The element to add.
	 * @returns {void}
	 */
	enqueue(item) {
		this._set.add(item);
	}

	/**
	 * Removes and returns the oldest enqueued item.
	 * @returns {T | undefined} The head of the queue of `undefined` if this queue is empty.
	 */
	dequeue() {
		const result = this._set[Symbol.iterator]().next();
		if (result.done) return;
		this._set.delete(result.value);
		return result.value;
	}
}

module.exports = Queue;