Signal Slot

Signals and Slots pattern written in Typescript.

Installation

npm install signal-slot

Usage

Creating a Signal

Create an instance of Signal with the specified type, i.e, string, number, etc.

import {Signal} from "signal-slot";

let onCompleted: Signal<number> = new Signal();

Binding a function callback

Bind a simple callback with do() and bind().

onCompleted.do((n: number) => {
	console.log("got a number", n);
}).bind();

You can also prioritize() a callback.

onCompleted.do((n: number) => {
	console.log("got a priority number", n);
}).prioritize().bind();

Or run the callback only once().

onCompleted.do((n: number) => {
	console.log("got a number once", n);
}).once().bind();

Execution Context

Use the context() when a function should be called as a method of an object.

onCompleted.do(this.methodHandler).context(this).bind();

Emitting a Signal

onCompleted.emit(299792458);

Built-in Notifier

The Notifier comes with a queue that can be controlled with start(), pause(), flush(), now(), delay(), and when() methods.

You can delegate emitting signals to the notifier if you need signals to emit in sequence. In other words, if the order of events is important to your app, you can use the Notifier to your advantage.

Create an instance of Notifier:

import {Notifier} from "signal-slot";

let notifier = new Notifier();

To add signal events to the queue:

let onStarted: Signal<string> = new Signal();
let onCompleted: Signal<string> = new Signal();
notifier.notify(onStarted).with("data").queue();
notifier.notify(onCompleted).with("data").queue();

To start processing the queue:

notifier.start();

To pause the queue:

notifier.pause();

Use now() to bypass the queue and notify immediately:

notifier.notify(onStarted).with("data").now();

Use delay() to bypass the queue and delay the notification:

notifier.notify(onCompleted).with("data").delay(1000);

Capturing signals and controlling when to start the queue

Sometimes there is a need to add signal events to the queue and fire them if and only when() a specific signal was dispatched.

For example your app needs to load configuration data async but the sequence of events needs to be maintained until the async is complete.

// Tell notifier to start only when onAsyncCompleted is notified
notifier.when(onAsyncCompleted).start();

// Capture sequence
notifier.notify(onLoaded).with("data").queue();
notifier.notify(onStarted).with("data").queue();
notifier.notify(onCompleted).queue();

// The following will trigger the queue start
notifier.notify(onAsyncCompleted).queue();

In the above scenario the queue will only start to process once a notification for the onAsyncCompleted signal is added to the queue.

Pro-Tips

Organize your events in a module or namespace.

export namespace Event {
	export const onLoaded: Signal<string> = new Signal();
	export const onCompleted: Signal<number> = new Signal();
}

Bind to events in your constructor.

class Subscriber {
	private message: string;
	constructor() {
		Event.onLoaded
			.do(this.loaded)
			.once()
			.context(this)
			.bind();
	}
	public loaded(message: string): void {
		this.message = message;
	}
}

Remove a callback

Event.onLoaded.unbind(this.callback);

Sequence Diagram

To-do

• Code comments and JsDoc

License

MIT License