PromiseStream 🌊

A stream-like promise that emits multiple values over time

Overview

What? 🤔

A simple building block that behaves like a regular Promise<T>, but can emit multiple values over time.

• Compatible with async/await (awaits completion)
• Provides built-in async iterator
• Contains configurable buffer size

Limitations & when to use? 🤷‍♂️

Like regular promises, a PromiseStream<T> is not cancellable, is hot, shared, and will replay the last value. Furthermore, no built-in operator support (like map or flatMap) is currently provided.

The limitations are intended. For extensive reactive apps I would recommend to use RxJS instead.

Roadmap ideas 💡

• Provide built-in RxJS compatibility utils
• Support different backpressure mechanisms

How to use 🌩

Install

npm install @dirkluijk/promise-stream

Creating a PromiseStream<T>

This works the same as a regular Promise, but you have three callbacks: next, complete and error.

import { PromiseStream } from '@dirkluijk/promise-stream';

const myStream = new PromiseStream<string>((next, complete, error) => {
    next('foo');
    next('bar');
    next('baz');
    complete();
})

• next always expects a value
• complete never expects a value
• error accepts an optional error value
• once completed or failed, no values are accepted anymore

Consuming a PromiseStream<T>

You can use callbacks:

myStream
    .iterate(value => {
        // executed when value is emitted
    })
    .then(() => {
        // executed when completed
    })
    .catch((error) => {
        // executed when failed
    })

Since a PromiseStream invokes the .then() callback upon completion, it is compatible with async/await:

try {
    await myStream.iterate(value => {
        // executed when value is emitted
    });
} catch (error) {
    // executed when failed
}

// executed when completed

Additionally, you can also use the async iterator:

try {
    for await (const value of myStream.asyncIterator()) {
        // executed when value is emitted
    };
} catch (error) {
    // executed when failed
}

// executed when completed