remitter

A tiny TypeScript friendly event emitter that supports lazy re-emitting events from other sources.

Install

1npm add remitter

Usage

1import { Remitter } from "remitter";
2
3interface EventData {
4  event1: string;
5  event2: void;
6}
7
8const remitter = new Remitter<EventData>();
9
10const disposer = remitter.on("event1", value => {
11  console.log("event1", value);
12});
13
14remitter.once("event1", value => {
15  console.log("event1-once", value);
16});
17
18remitter.has("event1"); // true
19
20remitter.emit("event1", "hello"); // logs "event1 hello" and "event1-once hello"
21
22remitter.emit("event1", "hello"); // logs "event1 hello"
23
24remitter.emit("event2"); // nothing logs
25
26disposer();
27remitter.emit("event1", "world"); // nothing logs
28
29remitter.clear("event2"); // remove all listeners for event2
30
31remitter.has(); // false
32
33remitter.dispose(); // removes all listeners and dispose tapped events

Listen to any event

1import { Remitter } from "remitter";
2
3interface EventData {
4  event1: string;
5  event2: string;
6}
7
8const remitter = new Remitter<EventData>();
9
10remitter.onAny(({ event, data }) => {
11  console.log(event, data);
12});
13
14remitter.emit("event1", "hello"); // logs "event1 hello"
15remitter.emit("event2", "world"); // logs "event2 world"

Listen to unhandled subscriber errors

1import { Remitter } from "remitter";
2
3interface EventData {
4  event1: string;
5  event2: string;
6}
7
8const remitter = new Remitter<EventData>();
9
10remitter.onError(error => {
11  console.log(error);
12});
13
14remitter.emit("event1", () => {
15  throw new Error("error");
16});
17
18remitter.emit("event2", async () => {
19  await new Promise(resolve => setTimeout(resolve, 100));
20  throw new Error("async-error");
21});

Remit

You may tap into other events easily with remit. It is lazy-executed when listener count of the event name grows from 0 to 1. It is disposed when listener count of the event name drops from 1 to 0.

1remitter.remit("cursor", () => {
2  const handler = ev => {
3    remitter.emit("cursor", { x: ev.clientX, y: ev.clientY });
4  };
5
6  window.addEventListener("mousemove", handler);
7
8  return () => {
9    window.removeListener("mousemove", handler);
10  };
11});
12
13// Remit callback does not execute until the first "cursor" listener is added
14remitter.on("cursor", value => {
15  console.log("cursor", value);
16});
17
18// Remit callback is disposed when no listener on the
19// "cursor" event. (`window.removeListener` triggered)
20remitter.clear("cursor");

The callback function can also be a pure function.

1const myCursorEvent = remitter => {
2  const handler = ev => {
3    remitter.emit("cursor", { x: ev.clientX, y: ev.clientY });
4  };
5
6  window.addEventListener("mousemove", handler);
7
8  return () => {
9    window.removeListener("mousemove", handler);
10  };
11};
12
13remitter.remit("cursor", myCursorEvent);

Acknowledgment

Huge thanks to @recursivefunk for giving away the NPM package name remitter.