aureooms/js-pubsub

/**
 * pubsub node that only notifies clients whose stamp is less than
 * the currently published stamp.
 *
 * @param {dict} subscriptions a ( key, stamp ) python-style dict
 * @param {comparable} stamp
 * @param {comparator} compare the comparison function used to compare stamps
 */
export const StampNode = function ( subscriptions, stamp, compare ) {
    this.subscriptions = subscriptions;
    this.stamp = stamp;
    this.compare = compare;
} ;


/**
 * Subscribes client with key *key* and stamp *stamp*. If
 * *stamp* < current stamp then we forward the current stamp
 * to client with key *key*.
 *
 * @param  {key} key      key of the subscriber
 * @param  {comparable} stamp   most up to date stamp the subscriber has
 * @param  {callback} forward the function to call when the stamp for a client
 *                    is outdated
 */

StampNode.prototype.subscribe = function ( key, stamp, forward ) {

    this.subscriptions.set( key, this.update( forward )( key, stamp ) );

};


StampNode.prototype.unsubscribe = function ( key ) {

    this.subscriptions.unset( key );

};


StampNode.prototype.publish = function ( stamp, forward ) {

    this.stamp = stamp;

    this.subscriptions.update( this.update( forward ) );

};

StampNode.prototype.update = function ( forward ) {

    const that = this;

    return function ( key, stamp ) {

        if ( that.compare( that.stamp, stamp ) > 0 ) {

            forward( key, that.stamp );

            return that.stamp;
        }

        else {

            return stamp;

        }

    };

};