from-emitter

inform an iterable when it is prematurely terminated by the consumer.

Install

yarn add @async-generators/from-emitter

This package's main entry points to a commonjs dist. The module entry points to a es2015 module dist. Both require native async-generator support, or be down-compiled with a webpack loader.

Exports

(default) from-emitter(emitter, onNext, onError, onDone [,selectNext][,selectError])

from-emitter() subscribes to onNext, onError and onDone and returns a (one-time) iterable-sequence of captured events. When the event listeners are called, the arguments are passed to selectNext(...args) and selectError(...args) to pick a value (defaults to the first argument). If the sequence completes (onDone), or the consumer terminates early, the event listeners are detached from the emitter and the iterable becomes disposed and cannot be iterated again.

source must be a node-js compliment event emitter, with the addListener and removeListener methods.

Example

example.js

const fromEmitter = require('./dist/commonjs').default;
const {EventEmitter} = require('events');

async function main() {
  let events = new EventEmitter();
  let source = fromEmitter(events, "data", "error", "close");
  let consumer = new Promise(async done => {
    for await (let item of source) {
      console.log(item);
    }
    console.log("...and we're done!")
    done();
  });

  events.emit("data", 1);
  events.emit("data", 2);
  events.emit("data", 3);
  events.emit("data", 4);
  events.emit("close");

  await consumer;
}

main().catch(console.log);

Execute with the latest node.js:

node example.js // or...
node --harmony-async-iteration example.js 

output:

1
2
3
4
...and we're done!

Typescript

This library is fully typed and can be imported using:

import fromEmitter from '@async-generators/from-emitter');

It is also possible to directly execute your properly configured typescript with ts-node:

ts-node --harmony_async_iteration example.ts