Observable

A library that provides classes that implement the Observer Pattern.

Installation

Deno

deno add jsr:@mishieck/observable

NPM

npx jsr add @mishieck/observable 

Bun

bun x jsr add @mishieck/observable 

Usage

import { type Event, Observable, type Observer } from "@mishieck/observable";
import { describe, it } from "@std/testing";
import { expect } from "@std/expect";

type EventName = "change" | "submit";
type ChangeEvent = Event<"change", string>;
type SubmitEvent = Event<"submit", string>;
type InputEventRecord = Record<EventName, string>;

describe("Observable", () => {
  it("should handle events", () => {
    const observableInput = new Observable<EventName, InputEventRecord>(
      ["change", "submit"],
    );

    let changeEventName = "";
    let changedInput = "";
    let submitEventName = "";
    let submittedInput = "";

    const observeChange: Observer<ChangeEvent> = ({ name, payload }) => {
      changeEventName = name;
      changedInput = payload;
    };

    const observeSubmit: Observer<SubmitEvent> = ({ name, payload }) => {
      submitEventName = name;
      submittedInput = payload;
    };

    observableInput.addObserver("change", observeChange);
    observableInput.addObserver("submit", observeSubmit);

    observableInput.notifyObservers("change", "O");
    expect(changeEventName).toEqual("change");
    expect(changedInput).toEqual("O");

    observableInput.notifyObservers("submit", "Observable");
    expect(submitEventName).toEqual("submit");
    expect(submittedInput).toEqual("Observable");

    observableInput.removeObserver("change", observeChange);
    observableInput.notifyObservers("change", "Ob");
    expect(changedInput).toEqual("O"); // Not changed
  });
});