TypeScript LiteEvent Events implementation

LiteEvent.ts

interface ILiteEvent<T> {
    on(handler: { (data?: T): void }) : void;
    off(handler: { (data?: T): void }) : void;
}

class LiteEvent<T> implements ILiteEvent<T> {
    private handlers: { (data?: T): void; }[] = [];

    public on(handler: { (data?: T): void }) : void {
        this.handlers.push(handler);
    }

    public off(handler: { (data?: T): void }) : void {
        this.handlers = this.handlers.filter(h => h !== handler);
    }

    public trigger(data?: T) {
        this.handlers.slice(0).forEach(h => h(data));
    }

    public expose() : ILiteEvent<T> {
        return this;
    }
}

LiteEventSample.ts

class Security{
    private readonly onLogin = new LiteEvent<string>();
    private readonly onLogout = new LiteEvent<void>();

    public get LoggedIn() { return this.onLogin.expose(); } 
    public get LoggedOut() { return this.onLogout.expose(); }

    // ... onLogin.trigger('bob');
}

function Init() {
    var security = new Security();

    var loggedOut = () => { /* ... */ }

    security.LoggedIn.on((username?) => { /* ... */ });
    security.LoggedOut.on(loggedOut);

    // ...

    security.LoggedOut.off(loggedOut);
}

Brilliance!

Simple and clear. Nice :)

Beautiful. Thank you.

good work！

Thanks!

Made a stricter version here, getting rid of optionality of data?: T in various signatures without impacting the case where T is void and should overall require no data parameter: https://gist.github.com/JasonKleban/924babb9c56d697c2d2a8f6f604eb3d4. I didn't want to revise this version because that version might turn out to have some negative qualities.

This was super helpful Jason, thank you! I do have one question: why do you use this.handlers.slice(0).forEach instead of just this.handlers.forEach?

@maucaro in case one of the earlier handlers modifies the handlers array in the handling of a particular event. It's just the saner general approach, but I guess you can adjust this for your situation.