Experimental PubSub impl. as a class

pub-sub-class.ts

class PubSub<T> {

    private handlers: { [key: string]: any[] } = {}

    public subscribe<E extends keyof T & string>(
        event: E,
        callback: (message: T[E]) => void
    ) {
        const list = this.handlers[event] ?? []
        list.push(callback)
        this.handlers[event] = list

        return callback
    }

    public unsubscribe<E extends keyof T & string>(
        event: E,
        callback: (message: T[E]) => void
    ) {
        let list = this.handlers[event] ?? []
        list = list.filter(h => h !== callback)
        this.handlers[event] = list
    }

    public publish<E extends keyof T & string>(
        event: E,
        message: T[E]
    ) {
        this.handlers[event].forEach(h => h(message))
    }

}

type Events = {
    warn: { errorCode: number, userMessage: string },
    error: { shitThatWentWrong: string },
}

const pubSub = new PubSub<Events>()

const subHandler = pubSub.subscribe("error", (message) => {
    console.log(message.shitThatWentWrong)
})

pubSub.publish("error", { shitThatWentWrong: "boom" })

// Allowed, correct handler type
pubSub.unsubscribe('error', subHandler)

// Not allowed, incorrect handler type
pubSub.unsubscribe('warn', subHandler)