@ersbeth/picosignal

PicoSignal

Minimal signal library written in typescript.

Signal programming is a particular type of event driven programming. This library provides:

• signals and slots (aka. events emitting and callbacks)
• observable values with auto-emitted signals on set

This library runs both in browser and on Node.js

Installation

npm install @ersbeth/picosignal

Usage

Signal

Basic signal

Declare a new signal and register a slot (aka. callback) to it. Then the slot will be called every time the signal is emitted :

let data = 0;
const signal = new Signal<void>();
signal.on(() => { data++ });

assert.equal(data, 0);
signal.emit();
assert.equal(data, 1);
signal.emit();
assert.equal(data, 2);

Signal with parameter

You can provide a parameter when emitting a signal. The parameter will be forwarded to the slot:

let data = 0;
const signal = new Signal<number>();
signal.on((value:number) => { data = value });

assert.equal(data, 0);
signal.emit(3);
assert.equal(data, 3);

Signal with multiple slots

You can provide multiple slots to a signal. They will be called by order of registration:

let data1 = 0;
let data2 = 2;
const signal = new Signal<number>();
signal.on((value:number) => { data1 += value });
signal.on((value:number) => { data2 *= value });

assert.equal(data1, 0);
assert.equal(data2, 2);
signal.emit(3);
assert.equal(data1, 3);
assert.equal(data2, 6);

Unsubscribe

The registering function returns an unregistering function which can be called at anytime to remove the connection:

    let data = 0;
    let signal = new Signal<void>();
    let unsubscribe = signal.on(() => { data++ });

    assert.equal(data, 0);
    signal.emit();
    assert.equal(data, 1);
    unsubscribe();
    signal.emit();
    assert.equal(data, 1); // data was not increased

Observable

Registration without execution

An Observable contains a value and a signal named onChanged that is automatically emitted each time value is set :

let computed = 0;
const observable = new Observable<number>(1);
observable.onChanged((value:number) => { computed = value * 2; });

assert.equal(computed, 0); // not 2, slot hasn't been called
observable.value = 2;
assert.equal(computed, 4);
observable.value = 5;
assert.equal(computed, 10);

Notice that the slot is NOT called with the current value upon registration. See subscribe below if you need such behaviour.

Registration with execution

You can use the subscribe method if you want both to:

• register your slot to an observable
• execute your slot with the current value of the observable

let computed = 0;
let observable = new Observable<number>(1);
observable.subscribe((value:number) => { computed = value * 2; });

assert.equal(computed, 2); // here slot has been called
observable.value = 2;
assert.equal(computed, 4);
observable.value = 5;
assert.equal(computed, 10);