event-emitters/dist.es2018/EventEmitterAsyncIterator.js

event emitters

import { Queue } from './Queue';
/**
 * An async iterator implemented with an efficient queue.
 *
 * Make the async iterator also fulfil AsyncIterable, which is pretty pointless
 * but needed to support certain APIs that are not implemented correctly.
 */
export class EventEmitterAsyncIterator {
    constructor(eventSource) {
        this.eventSource = eventSource;
        this.emitted = new Queue();
        // this will only contain listeners when `emitted` is empty
        this.pendingListens = new Queue();
        this.onEmit = this.onEmit.bind(this);
        eventSource.subscribe(this.onEmit);
    }
    onEmit(value) {
        if (this.pendingListens.length) {
            this.pendingListens.dequeue()({ done: false, value });
        }
        else {
            this.emitted.enqueue(value);
        }
    }
    next() {
        if (this.emitted.length) {
            return Promise.resolve({ done: false, value: this.emitted.dequeue() });
        }
        else {
            return new Promise((resolve) => {
                this.pendingListens.enqueue(resolve);
            });
        }
    }
    return() {
        this.eventSource.unsubscribe(this.onEmit);
        this.emitted.destroy();
        this.pendingListens.destroy();
        return Promise.resolve({ value: undefined, done: true });
    }
    throw(error) {
        this.eventSource.unsubscribe(this.onEmit);
        this.emitted.destroy();
        this.pendingListens.destroy();
        return Promise.reject(error);
    }
    // *sigh*
    [Symbol.asyncIterator]() {
        return this;
    }
}
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