Orderly Queue

Implementation of a promise-based FIFO queuing system using ES2017 async generators.

   

npm: npm i orderly-queue -S
Babel: babel-plugin-syntax-async-generators

• Takes a function that returns a promise (or Promise.all)
• Invokes the promise and yields the eventual result
• Awaits the completion of the task before beginning the next
• Implements a pseudo-observable for next and error
• Passes the returned props along to the next task

Usage

import Queue from 'orderly-queue';
 
const queue = Queue({ value: ['Blueberries'], next: console.log });
 
queue.process(fruits => Promise.resolve([...fruits, 'Apples']));
queue.process(fruits => Promise.resolve([...fruits, 'Bananas']));
queue.process(fruits => Promise.resolve([...fruits, 'Raspberries']));
 
// > ['Blueberries']
// > ['Blueberries', 'Apples']
// > ['Blueberries', 'Apples', 'Bananas']
// > ['Blueberries', 'Apples', 'Bananas', 'Raspberries']

Each task will wait before the completion of the current task, meaning you can safely assume the order of fruits no matter how long it takes for a single task to complete.

Errors

Any errors that are raised will be passed to the error function, however the items in the queue will continue to be invoked one-at-a-time passing in the props from the last successful invocation.

import Queue from 'orderly-queue';
 
const queue = Queue({ value: ['Blueberries'], next: console.log, error: console.log });
 
queue.process(fruits => Promise.resolve([...fruits, 'Apples']));
queue.process(fruits => Promise.reject('Error: Fruitless...'));
queue.process(fruits => Promise.resolve([...fruits, 'Bananas']));
queue.process(fruits => Promise.resolve([...fruits, 'Raspberries']));
 
// > ['Blueberries']
// > ['Blueberries', 'Apples']
// > Error: Fruitless...
// > ['Blueberries', 'Apples', 'Bananas']
// > ['Blueberries', 'Apples', 'Bananas', 'Raspberries']

In cases where you wish to end the iterator early you can invoke the abort method — perhaps in response to an error being raised. Any queued tasks will not be run.

const queue = Queue({ value: ['Blueberries'], next: console.log, error: console.log });
 
// ...
 
queue.abort();