queue

Asynchronous function queue with adjustable concurrency.
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// ==UserScript==
// @name               queue
// @description        Asynchronous function queue with adjustable concurrency.
// @author             Jesse Tane
// @namespace          https://github.com/jessetane/queue
// @version            7.0.0
// @license            MIT
// ==/UserScript==
 
var { Queue, QueueEvent } = (function (exports) {
  'use strict';
 
  const has = Object.prototype.hasOwnProperty;
 
  /**
   * Since CustomEvent is only supported in nodejs since version 19,
   * you have to create your own class instead of using CustomEvent
   * @see https://github.com/nodejs/node/issues/40678
   * */
  class QueueEvent extends Event {
    constructor (name, detail) {
      super(name);
      this.detail = detail;
    }
  }
 
  class Queue extends EventTarget {
    constructor (options = {}) {
      super();
      const { concurrency = Infinity, timeout = 0, autostart = false, results = null } = options;
      this.concurrency = concurrency;
      this.timeout = timeout;
      this.autostart = autostart;
      this.results = results;
      this.pending = 0;
      this.session = 0;
      this.running = false;
      this.jobs = [];
      this.timers = [];
      this.addEventListener('error', this._errorHandler);
    }
 
    _errorHandler (evt) {
      this.end(evt.detail.error);
    }
 
    pop () {
      return this.jobs.pop()
    }
 
    shift () {
      return this.jobs.shift()
    }
 
    indexOf (searchElement, fromIndex) {
      return this.jobs.indexOf(searchElement, fromIndex)
    }
 
    lastIndexOf (searchElement, fromIndex) {
      if (fromIndex !== undefined) return this.jobs.lastIndexOf(searchElement, fromIndex)
      return this.jobs.lastIndexOf(searchElement)
    }
 
    slice (start, end) {
      this.jobs = this.jobs.slice(start, end);
      return this
    }
 
    reverse () {
      this.jobs.reverse();
      return this
    }
 
    push (...workers) {
      const methodResult = this.jobs.push(...workers);
      if (this.autostart) this._start();
      return methodResult
    }
 
    unshift (...workers) {
      const methodResult = this.jobs.unshift(...workers);
      if (this.autostart) this._start();
      return methodResult
    }
 
    splice (start, deleteCount, ...workers) {
      this.jobs.splice(start, deleteCount, ...workers);
      if (this.autostart) this._start();
      return this
    }
 
    get length () {
      return this.pending + this.jobs.length
    }
 
    start (callback) {
      if (this.running) throw new Error('already started')
      let awaiter;
      if (callback) {
        this._addCallbackToEndEvent(callback);
      } else {
        awaiter = this._createPromiseToEndEvent();
      }
      this._start();
      return awaiter
    }
 
    _start () {
      this.running = true;
      if (this.pending >= this.concurrency) {
        return
      }
      if (this.jobs.length === 0) {
        if (this.pending === 0) {
          this.done();
        }
        return
      }
      const job = this.jobs.shift();
      const session = this.session;
      const timeout = (job !== undefined) && has.call(job, 'timeout') ? job.timeout : this.timeout;
      let once = true;
      let timeoutId = null;
      let didTimeout = false;
      let resultIndex = null;
      const next = (error, ...result) => {
        if (once && this.session === session) {
          once = false;
          this.pending--;
          if (timeoutId !== null) {
            this.timers = this.timers.filter(tID => tID !== timeoutId);
            clearTimeout(timeoutId);
          }
          if (error) {
            this.dispatchEvent(new QueueEvent('error', { error, job }));
          } else if (!didTimeout) {
            if (resultIndex !== null && this.results !== null) {
              this.results[resultIndex] = [...result];
            }
            this.dispatchEvent(new QueueEvent('success', { result: [...result], job }));
          }
          if (this.session === session) {
            if (this.pending === 0 && this.jobs.length === 0) {
              this.done();
            } else if (this.running) {
              this._start();
            }
          }
        }
      };
      if (timeout) {
        timeoutId = setTimeout(() => {
          didTimeout = true;
          this.dispatchEvent(new QueueEvent('timeout', { next, job }));
          next();
        }, timeout);
        this.timers.push(timeoutId);
      }
      if (this.results != null) {
        resultIndex = this.results.length;
        this.results[resultIndex] = null;
      }
      this.pending++;
      this.dispatchEvent(new QueueEvent('start', { job }));
      job.promise = job(next);
      if (job.promise !== undefined && typeof job.promise.then === 'function') {
        job.promise.then(function (result) {
          return next(undefined, result)
        }).catch(function (err) {
          return next(err || true)
        });
      }
      if (this.running && this.jobs.length > 0) {
        this._start();
      }
    }
 
    stop () {
      this.running = false;
    }
 
    end (error) {
      this.clearTimers();
      this.jobs.length = 0;
      this.pending = 0;
      this.done(error);
    }
 
    clearTimers () {
      this.timers.forEach(timer => {
        clearTimeout(timer);
      });
      this.timers = [];
    }
 
    _addCallbackToEndEvent (cb) {
      const onend = evt => {
        this.removeEventListener('end', onend);
        cb(evt.detail.error, this.results);
      };
      this.addEventListener('end', onend);
    }
 
    _createPromiseToEndEvent () {
      return new Promise((resolve, reject) => {
        this._addCallbackToEndEvent((error, results) => {
          if (error) reject(error);
          else resolve(results);
        });
      })
    }
 
    done (error) {
      this.session++;
      this.running = false;
      this.dispatchEvent(new QueueEvent('end', { error }));
    }
  }
 
  exports.Queue = Queue;
  exports.QueueEvent = QueueEvent;
 
  return exports;
 
})({});