evnty/build/listener-registry.js

Async-first, reactive event handling library for complex event flows in browser and Node.js

import { err } from "./dispatch-result.js";
export class ListenerRegistry {
    #listeners = new Map();
    #snapshot = null;
    [Symbol.toStringTag] = 'ListenerRegistry';
    get size() {
        return this.#listeners.size;
    }
    has(listener) {
        return this.#listeners.has(listener);
    }
    lacks(listener) {
        return !this.has(listener);
    }
    off(listener) {
        const entry = this.#listeners.get(listener);
        if (!entry) {
            return false;
        }
        this.#listeners.delete(listener);
        this.#snapshot = null;
        entry.onRemove?.();
        return true;
    }
    on(listener, onRemove) {
        if (this.has(listener)) {
            return false;
        }
        this.#listeners.set(listener, {
            once: false,
            onRemove
        });
        this.#snapshot = null;
        return true;
    }
    once(listener, onRemove) {
        if (this.has(listener)) {
            return false;
        }
        this.#listeners.set(listener, {
            once: true,
            onRemove
        });
        this.#snapshot = null;
        return true;
    }
    clear() {
        for (const entry of this.#listeners.values()){
            entry.onRemove?.();
        }
        this.#listeners.clear();
        this.#snapshot = null;
    }
    dispatch(...values) {
        const listeners = this.#listeners;
        if (listeners.size === 0) {
            return [];
        }
        let ordered = this.#snapshot;
        if (!ordered) {
            const snapshot = new Array(listeners.size);
            let index = 0;
            for (const fn of listeners.keys()){
                snapshot[index++] = fn;
            }
            snapshot.length = index;
            ordered = snapshot;
            this.#snapshot = snapshot;
        }
        if (ordered.length === 0) {
            return [];
        }
        const results = new Array(ordered.length);
        const argCount = values.length;
        for(let index = 0; index < ordered.length; index++){
            const fn = ordered[index];
            if (listeners.get(fn)?.once) {
                this.off(fn);
            }
            const invoke = fn;
            try {
                switch(argCount){
                    case 0:
                        results[index] = invoke();
                        break;
                    case 1:
                        results[index] = invoke(values[0]);
                        break;
                    case 2:
                        results[index] = invoke(values[0], values[1]);
                        break;
                    default:
                        results[index] = invoke(...values);
                        break;
                }
            } catch (error) {
                results[index] = err(error);
            }
        }
        return results;
    }
}

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