Extending Evt

It is common practice to create classes that extends EventEmitter . 
As a general rule of thumb, we tend to avoid inheritance in favor of other patterns but if you want to do it there is how.
import { Evt, to } from "evt";
​
class MySocket extends Evt<
    ["connect", void] |
    ["disconnect", { cause: "remote" | "local" } ] |
    ["error", Error]
    > {
​
    public readonly address: string;
​
    constructor(
        params: { 
            address: string; 
        }
    ) {
​
        super();
​
        const { address } = params;
​
        this.address = address;
​
        setTimeout(
            () => this.post(["connect", undefined]),
            300
        );
​
        setTimeout(
            () => this.post(["disconnect", { "cause": "local" }]),
            2000
        );
​
    }
​
}
​
​
​
const socket = new MySocket({ 
    "address": "wss://example.com"
});
​
(async ()=> {
​
  await socket.waitFor(to("connect"));
​
  console.log("Socket connected");
​
})();
​
socket.$attach(to("error"), error => { throw error });
​
socket.$attach(
    data=> data[0] === "disconnect" ? [ data[1] ] : null, //Just so you know this is what the to() operator do
    ({ cause })=> console.log(`socket disconnect (${cause})`)
);
​Run the browser​
Now we encourage favoring composition over inheritance and having one EVT instance for each events type.
import { Evt } from "evt";
import type { NonPostableEvt } from "evt";
​
class MySocket {
​
    public readonly address: string;
    
    /*
    We use NonPostableEvt instead of Evt so we make clear that
    the connect disconnect and error events are not supposed to
    be posted from outside the class implementation.
    */
​
    public readonly evtConnect: NonPostableEvt<void> = new Evt();
    
    //Equivalent of the line above but it prevent you from having to import the ToNonPostable helper type
    public readonly evtDisconnect = Evt.asNonPostable(
        Evt.create<{ 
            cause: "local" | "remote" 
        }>()
    ); 
    
    public readonly evtError= Evt.asNonPostable(
        Evt.create<Error>()
    );
​
    constructor(
        params: { 
            address: string; 
        }
    ) {
​
        const { address } = params;
​
        this.address = address;
​
​
        setTimeout(
            () => Evt.asPostable(this.evtConnect).post(),
            300
        );
​
        setTimeout(
            () => Evt.asPostable(this.evtDisconnect).post({ "cause": "local" }),
            2000
        );
​
    }
​
}
​
const socket = new MySocket({ 
    "address": "wss://example.com"
});
​
(async ()=> {
​
  await socket.evtConnect.waitFor();
​
  console.log("socket connected [bis]");
​
})();
​
socket.evtError.attach(error => { throw error });
​
socket.evtDisconnect.attach(
    ({ cause }) => console.log(`socket disconnect (${cause})`)
);
​Run in the browser​
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