@ersbeth/picosignal
v0.0.3
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Minimal signal/slot/observable library for JS/TS files
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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);