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.
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import { Evt, to } from "evt";
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class MySocket extends Evt<
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["connect", void] |
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["disconnect", { cause: "remote" | "local" } ] |
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["error", Error]
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> {
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public readonly address: string;
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constructor(
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params: {
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address: string;
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}
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) {
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super();
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const { address } = params;
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this.address = address;
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setTimeout(
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() => this.post(["connect", undefined]),
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300
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);
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setTimeout(
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() => this.post(["disconnect", { "cause": "local" }]),
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2000
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);
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}
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}
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const socket = new MySocket({
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"address": "wss://example.com"
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});
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(async ()=> {
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await socket.waitFor(to("connect"));
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console.log("Socket connected");
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})();
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socket.$attach(to("error"), error => { throw error });
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socket.$attach(
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data=> data[0] === "disconnect" ? [ data[1] ] : null, //Just so you know this is what the to() operator do
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({ cause })=> console.log(`socket disconnect (${cause})`)
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);
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Now we encourage favoring composition over inheritance and having one EVT instance for each events type.
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import { Evt } from "evt";
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import type { NonPostableEvt } from "evt";
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class MySocket {
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public readonly address: string;
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/*
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We use NonPostableEvt instead of Evt so we make clear that
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the connect disconnect and error events are not supposed to
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be posted from outside the class implementation.
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*/
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public readonly evtConnect: NonPostableEvt<void> = new Evt();
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//Equivalent of the line above but it prevent you from having to import the ToNonPostable helper type
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public readonly evtDisconnect = Evt.asNonPostable(
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Evt.create<{
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cause: "local" | "remote"
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}>()
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);
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public readonly evtError= Evt.asNonPostable(
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Evt.create<Error>()
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);
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constructor(
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params: {
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address: string;
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}
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) {
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const { address } = params;
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this.address = address;
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setTimeout(
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() => Evt.asPostable(this.evtConnect).post(),
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300
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);
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setTimeout(
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() => Evt.asPostable(this.evtDisconnect).post({ "cause": "local" }),
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2000
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);
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}
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}
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const socket = new MySocket({
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"address": "wss://example.com"
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});
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(async ()=> {
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await socket.evtConnect.waitFor();
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console.log("socket connected [bis]");
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})();
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socket.evtError.attach(error => { throw error });
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socket.evtDisconnect.attach(
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({ cause }) => console.log(`socket disconnect (${cause})`)
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);
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Last modified 9mo ago
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