queue-promise

queue-promise

queue-promise is a small, dependency-free library for promise-based queues. It will resolve enqueued functions concurrently at a given speed. When a task is being resolved or rejected, an event will be emitted.

Installation

$ npm install queue-promise

Usage

import Queue from "queue-promise";

const queue = new Queue({
  concurrent: 1,  // resolve 1 task at a time
  interval: 2000, // resolve new tasks each 2000ms,
  start: true,    // automatically resolve new tasks when they are added
});

queue.on("resolve", data => console.log(data));
queue.on("reject", error => console.error(error));

queue.enqueue(asyncTaskA); // resolved/rejected after 0s
queue.enqueue(asyncTaskB); // resolved/rejected after 2s
queue.enqueue(asyncTaskC); // resolved/rejected after 4s
queue.enqueue(asyncTaskD); // resolved/rejected after 6s

API

new Queue(options)

Create a new Queue instance.

Option	Default	Description
concurrent	5	How many tasks can be handled at the same time
interval	500	How often should new tasks be handled (in ms)
start	true	Whether we should automatically resolve new tasks as soon as they are added

public .enqueue(task)/.add(task)

Puts a new task on the stack. Tasks should be an async function or return a promise. Throws an error if the provided task is not a valid function.

Example:

async function getRepos(user) {
  return await github.getRepos(user);
};

queue.enqueue(getRepos("userA"));
queue.enqueue(getRepos("userB"));

// …equivalent to:
queue.enqueue([
  getRepos("userA"),
  getRepos("userB"),
]);

public .dequeue()

Resolves n concurrent promises from the queue. Uses global Promises.

Example:

queue.enqueue(getRepos("userA"));
queue.enqueue(getRepos("userB"));

// If "concurrent" is set to 1, only one promise is resolved on dequeue:
const userA = await queue.dequeue();
const userB = await queue.dequeue();

// If "concurrent" is set to 2, two promises are resolved concurrently:
const users = await queue.dequeue();

public .on(event, callback)

Sets a callback for an event. You can set callback for those events: start, stop, resolve, reject, end.

Example:

queue.enqueue([…]);

queue.on("resolve", output => …);
queue.on("reject", output => …);
queue.on("end", () => …);

public .start()

Starts the queue – it will automatically dequeue tasks periodically. Emits start event.

public .stop()

Stops the queue. Emits stop event.

public .clear()

Removes all tasks from the queue.

public .started

Whether the queue has been started or not.

public .isEmpty

Whether the queue is empty, i.e. there's no tasks.

Tests

$ npm test