Repeater.js

The missing constructor for creating safe async iterators.

For more information, visit repeater.js.org.

Installation

Repeater.js is available on npm in the CommonJS and ESModule formats.

$ npm install @repeaterjs/repeater

$ yarn add @repeaterjs/repeater

Requirements

The core @repeaterjs/repeater module has no dependencies, but requires the following globals in order to work:
- Promise
- WeakMap
- Symbol
- Symbol.iterator
- Symbol.asyncIterator

In addition, repeaters are most useful when used via async/await and for await…of syntax. You can transpile your code with babel or typescript to support enviroments which lack these features.

Examples

Logging timestamps with setInterval

``js
import { Repeater } from "@repeaterjs/repeater";

const timestamps = new Repeater(async (push, stop) => {
push(Date.now());
const interval = setInterval(() => push(Date.now()), 1000);
await stop;
clearInterval(interval);
});

(async function() {
let i = 0;
for await (const timestamp of timestamps) {
console.log(timestamp);
i++;
if (i >= 10) {
console.log("ALL DONE!");
break; // triggers clearInterval above
}
}
})();
`

Creating a repeater from a websocket

`js
import { Repeater } from "@repeaterjs/repeater";

const socket = new WebSocket("ws://echo.websocket.org");
const messages = new Repeater(async (push, stop) => {
socket.onmessage = (ev) => push(ev.data);
socket.onerror = () => stop(new Error("WebSocket error"));
socket.onclose = () => stop();
await stop;
socket.close();
});

(async function() {
for await (const message of messages) {
console.log(message);
if (message === "close") {
console.log("Closing!");
break; // closes the socket
}
}
})();

socket.onopen = () => {
socket.send("hello"); // "hello"
socket.send("world"); // "world"
socket.send("close"); // "close", "Closing!"
};
`

Listening for the Konami Code and canceling if Escape is pressed

`js
import { Repeater } from "@repeaterjs/repeater";

const keys = new Repeater(async (push, stop) => {
const listener = (ev) => {
if (ev.key === "Escape") {
stop();
} else {
push(ev.key);
}
};
window.addEventListener("keyup", listener);
await stop;
window.removeEventListener("keyup", listener);
});

const konami = ["ArrowUp", "ArrowUp", "ArrowDown", "ArrowDown", "ArrowLeft", "ArrowRight", "ArrowLeft", "ArrowRight", "b", "a"];

(async function() {
let i = 0;
for await (const key of keys) {
if (key === konami[i]) {
i++;
} else {
i = 0;
}
if (i >= konami.length) {
console.log("KONAMI!!!");
break; // removes the keyup listener
}
}
})();
`

Converting an observable to an async iterator

`js
import { Subject } from "rxjs";
import { Repeater } from "@repeaterjs/repeater";

const observable = new Subject();
const repeater = new Repeater(async (push, stop) => {
const subscription = observable.subscribe({
next: (value) => push(value),
error: (err) => stop(err),
complete: () => stop(),
});
await stop;
subscription.unsubscribe();
});

(async function() {
try {
for await (const value of repeater) {
console.log("Value: ", value);
}
} catch (err) {
console.log("Error caught: ", err);
}
})();
observable.next(1);
// Value: 1
observable.next(2);
// Value: 2
observable.error(new Error("Hello from observable"));
// Error caught: Error: Hello from observable
``