Turns out that I needed an even smaller type of event: the signal. It is an event that has no data; it just fires. The Strongly Typed Events project started with the IEvent<TSender, TArgument> that was styled after the way .Net does event handling. Then the ISimpleEvent<TArgument> was added in 0.2.0, for scenarios when no sender is necessary. Now I’ve added the ISignal to version 0.3.0.
Why would we need another event type?
While programming a new TypeScript project, I got the need for a timer mechanism. I only need an event without data – much like a simple egg-timer. Implementing those events as an ISimpleEvent<void> looks ridiculous, that’s why I created the ISignal and its counterparts.
Traffic light example
Its usage is best illustrated with a piece of example code. Let’s create a somewhat static traffic light that will switch colors based on time. Remember: I’m Dutch, so the middle color will be orange!
class TrafficLight {
private _signals = new SignalList();
private _color = 'red';
public constructor(
public greenMs: number,
public orangeMs: number,
public redMs: number
) {
this.onSwitchToGreen.subscribe(() => this._color = 'green');
this.onSwitchToOrange.subscribe(() => this._color = 'orange');
this.onSwitchToRed.subscribe(() => this._color = 'red');
this.internalStart();
}
public get color(): string {
return this._color;
}
public get onSwitchToGreen(): ISignal {
return this._signals.get('green').asEvent();
}
public get onSwitchToRed(): ISignal {
return this._signals.get('red').asEvent();
}
public get onSwitchToOrange(): ISignal {
return this._signals.get('orange').asEvent();
}
private internalStart(): void {
window.setTimeout(() => {
this._signals.get('green').dispatch();
window.setTimeout(() => {
this._signals.get('orange').dispatch();
window.setTimeout(() => {
this._signals.get('red').dispatch();
this.internalStart();
}, this.orangeMs);
}, this.greenMs)
}, this.redMs)
}
}
You can subscribe and unsubscribe from the signals in the usual way:
var light = new TrafficLight(5000, 1500, 10000);
light.onSwitchToGreen.subscribe(() => console.log('Light is green.'));
light.onSwitchToOrange.subscribe(() => console.log('Light is orange.'));
light.onSwitchToRed.subscribe(() => console.log('Light is red.'));
The usual suspects
All of the usual suspects are present:
- ISignal – interface for signal event implementation and exposure.
- SignalDispatcher – implementation of a signal with a dispatch method.
- SignalList – implements named storage of auto created signals. Useful you need to implement a lot of them.
- SignalHandlingBase – to give your class named signal capabilities.
Other changes
I’ve removed the version numbers from the file names which makes updating easier. The tests are now wrapped in modules and have a string comment attached to them.