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/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
const UNCAUGHT_ERROR = 'An error event was emitted for which there was no listener.';
const BAD_LISTENER = 'The event listener must be a function.';
const { ns } = require('../namespace');
const event = ns();
// Utility function to access given event `target` object's event listeners for
// the specific event `type`. If listeners for this type does not exists they
// will be created.
const observers = function observers(target, type) {
let listeners = event(target);
return type in listeners ? listeners[type] : listeners[type] = [];
};
/**
* Registers an event `listener` that is called every time events of
* specified `type` is emitted on the given event `target`.
* @param {Object} target
* Event target object.
* @param {String} type
* The type of event.
* @param {Function} listener
* The listener function that processes the event.
*/
function on(target, type, listener) {
if (typeof(listener) !== 'function')
throw new Error(BAD_LISTENER);
let listeners = observers(target, type);
if (!~listeners.indexOf(listener))
listeners.push(listener);
}
exports.on = on;
/**
* Registers an event `listener` that is called only the next time an event
* of the specified `type` is emitted on the given event `target`.
* @param {Object} target
* Event target object.
* @param {String} type
* The type of the event.
* @param {Function} listener
* The listener function that processes the event.
*/
function once(target, type, listener) {
on(target, type, function observer() {
off(target, type, observer);
listener.apply(target, arguments);
});
}
exports.once = once;
/**
* Execute each of the listeners in order with the supplied arguments.
* All the exceptions that are thrown by listeners during the emit
* are caught and can be handled by listeners of 'error' event. Thrown
* exceptions are passed as an argument to an 'error' event listener.
* If no 'error' listener is registered exception will be logged into an
* error console.
* @param {Object} target
* Event target object.
* @param {String} type
* The type of event.
* @params {Object|Number|String|Boolean} message
* First argument that will be passed to listeners.
* @params {Object|Number|String|Boolean} ...
* More arguments that will be passed to listeners.
*/
function emit(target, type, message /*, ...*/) {
for each (let item in emit.lazy.apply(emit.lazy, arguments))
item;
}
/**
* This is very experimental feature that you should not use unless absolutely
* need it. Also it may be removed at any point without any further notice.
*
* Creates lazy iterator of return values of listeners. You can think of it
* as lazy array of return values of listeners for the `emit` with the given
* arguments.
*/
emit.lazy = function lazy(target, type, message /*, ...*/) {
let args = Array.slice(arguments, 2)
let listeners = observers(target, type).slice()
while (listeners.length) {
try {
yield listeners.shift().apply(target, args);
}
catch (error) {
// If exception is not thrown by a error listener and error listener is
// registered emit `error` event. Otherwise dump exception to the console.
if (type !== 'error' && observers(target, 'error').length)
emit(target, 'error', error);
else
console.exception(error);
}
}
}
exports.emit = emit;
/**
* Removes an event `listener` for the given event `type` on the given event
* `target`. If no `listener` is passed removes all listeners of the given
* `type`. If `type` is not passed removes all the listeners of the given
* event `target`.
* @param {Object} target
* The event target object.
* @param {String} type
* The type of event.
* @param {Function} listener
* The listener function that processes the event.
*/
function off(target, type, listener) {
let length = arguments.length;
if (length === 3) {
let listeners = observers(target, type);
let index = listeners.indexOf(listener);
if (~index)
listeners.splice(index, 1);
}
else if (length === 2) {
observers(target, type).splice(0);
}
else if (length === 1) {
let listeners = event(target);
Object.keys(listeners).forEach(function(type) delete listeners[type]);
}
}
exports.off = off;
/**
* Returns a number of event listeners registered for the given event `type`
* on the given event `target`.
*/
function count(target, type) {
return observers(target, type).length;
}
exports.count = count;
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