wake-up / sleep listeners

wake-up-sleep.ts

class Test<A> {
    private _value: A;
    private _listeners: ((a:A)=>void)[] = [];
    private _onWakeUp: () => {};
    private _onSleep: () => {};

    public constructor(value: A) {
        this._value = value;
    }

    public listen(listener: (a:A)=>void): ()=>void {
        if (this._listeners.length == 0) {
            this._onWakeUp();
        }
        this._listeners.push(listener);
        return () => {
            for (var i = 0; i < this._listeners.length; ++i) {
                if (this._listeners[i] === listener) {
                    this._listeners.splice(i, 1);
                    if (this._listeners.length == 0) {
                        this._onSleep();
                    }
                    return;
                }
            }
        };
    }

    public map<B>(fn: (a:A)=>B): Test<B> {
        var x = new Test(
            fn(this._value)
        );
        x._onWakeUp = () => {
          ...
        }
        x._onSleep = ...
    }
}