@soil/arch/build/es6/arch/src/chan.js

Architectural constructs for web applications.

/**
 * Type-safe event mini-bus, or publisher/subscriber system. Useful for
 * communicating distant components.
 */
export function chan() {
    var listeners = [];
    /**
     * Unsubscribe a listener from the channel.
     */
    function unsub(listener) {
        listeners = listeners.filter(function (l) { return l !== listener; });
    }
    return {
        /**
         * Subscribe a listener to the channel. A function is returned which can
         * be called to unsubscribe that same listener. An optional second
         * argument may be passed to specify the maximum number of times the
         * listener will be notified before automatically unsubscribing it.
         */
        sub: function (listener, times) {
            var timesIsDefined = times !== undefined;
            var listenerWrapper = function (msg) {
                if (timesIsDefined && --times === 0) {
                    unsub(listenerWrapper);
                }
                listener(msg);
            };
            listeners.push(listenerWrapper);
            return function () { return unsub(listenerWrapper); };
        },
        /**
         * Send an event to all listeners, with a payload.
         */
        pub: function (msg) {
            listeners.slice().forEach(function (l) { return l(msg); });
        },
        /**
         * Return the number of listeners on the channel.
         */
        get size() {
            return listeners.length;
        },
        /**
         * Unsubscribe all listeners from the channel.
         */
        clear: function () {
            listeners.length = 0;
        }
    };
}
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