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events-to-async

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  • License MIT

Treat EventEmitter-like object using Async/Await, Async Iterator.

Package Exports

  • events-to-async

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (events-to-async) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

events-to-async

Treat EventEmitter-like object using Async/Await and Async Iterator.

Similar one of Node.js events.on and event.once, but it is generic.

Features

  • events to Async Iterator
  • once event to a Promise
  • support EventEmitter-like libraries

Install

Install with npm:

npm install events-to-async

Usage

once an event to Promise

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
setTimeout(() => {
    events.emit("change", 1);
});
const event = await once((handler) => event.once("change", handler));
console.log(event); // => [1]

on events to AsyncIterator

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
const asyncIterator = on((handler) => {
    event.on("change", handler); // Listen
    return () => {
        // This function is called on occuring error or `break;`
        event.off("change", handler); // UnListen
    }
});
setTimeout(() => {
    events.emit("change", 1);
    events.emit("change", 2);
    events.emit("change", 3);
});
for await(const event of asyncIterator) {
    console.log(event); // [1] → [2] → [3]
}
// Unreachable here

You can stop the async iterator by using break;

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
const asyncIterator = on((handler) => {
    events.on("change", handler); // Listen
    return () => {
        // This function is called on occuring error or `break;`
        events.off("change", handler); // UnListen
    }
});
setTimeout(() => {
    events.emit("change", 1);
    events.emit("change", 2);
    events.emit("change", 3);
});
for await(const [num] of asyncIterator) {
    console.log(num); // 1 → 2 → 3
    if (num === 3) {
        break;
    }
}
console.log("4!!!");

AbortController supports

You can cancel events using AbortController.

once an event with cancel

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
const abortController = new AbortController();
const event = once((handler) => {
    event.once("change", handler);
    return () => {
        event.off("change", handler);  // call it when occur error or abort
    }
}, { signal: abortController.signal });
// Abort
abortController.abort();
await event; // => throw Abort Error

on events with cancel

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
const abortController = new AbortController();
const asyncIterator = on((handler) => {
    events.on("change", handler);
    return () => {
        events.off("change", handler);
    }
}, { signal: abortController.signal });
// Abort
abortController.abort();

TypeScript supports

on<T> and once<T> support generics that represent iterated value.

📝 on<T> and once<T> always return an array

import { EventEmitter } from "events";
import { on } from "events-to-async";

const events = new EventEmitter();
type Event = number;
const asyncIterator = on<[Event]>((handler) => {
    events.on("change", handler);
    return () => events.off("change", handler)
});
setTimeout(() => {
    events.emit("change", 1);
    events.emit("change", 2);
    events.emit("change", 3);
});
for await(const event of asyncIterator) {
    console.log(event); // [1] → [2] → [3]
}

Yet another EventEmitter supports

This library aim to support yet another events module like eventmit.

import { eventmit } from "eventmit";
import { on } from "events-to-async";

type Event = { key: string };
const events = eventmit<Event>();
const asyncIterator = on<[Event]>((handler) => {
    events.on(handler);
    return () => events.off(handler);
});
setTimeout(() => {
    events.emit({ key: "value" });
});
for await (const event of asyncIterator) {
    assert.deepStrictEqual(event, [{ key: "value" }]);
    break;
}

Changelog

See Releases page.

Running tests

Install devDependencies and Run npm test:

npm test

Contributing

Pull requests and stars are always welcome.

For bugs and feature requests, please create an issue.

  1. Fork it!
  2. Create your feature branch: git checkout -b my-new-feature
  3. Commit your changes: git commit -am 'Add some feature'
  4. Push to the branch: git push origin my-new-feature
  5. Submit a pull request :D

Author

License

MIT © azu