parallel-universe/Blocker.js

The set of async flow control structures and promise utils.

'use strict';

/**
 * Provides mechanism for blocking async processes and unblocking them from an external context.
 *
 * @template T The value that can be passed to {@link unblock} to resolve the {@link block} promise.
 */
class Blocker {
    /**
     * `true` if {@link Blocker} is blocked and wasn't unblocked yet, or `false` otherwise.
     */
    get isBlocked() {
        return this._unblock !== undefined;
    }
    /**
     * Returns promises that is fulfilled with the result passed to {@link unblock}. If blocker is already blocked
     * then the same promise is returned.
     */
    block() {
        if (this._promise === undefined) {
            this._promise = new Promise(resolve => {
                this._unblock = resolve;
            });
        }
        return this._promise;
    }
    /**
     * Fulfills the promise returned from {@link block}. If the blocker isn't blocked then no-op.
     */
    unblock(value) {
        const { _unblock } = this;
        if (_unblock !== undefined) {
            this._unblock = undefined;
            _unblock(value);
        }
    }
}

exports.Blocker = Blocker;