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/* 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";
module.metadata = {
"stability": "unstable"
};
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('../core/namespace');
const event = ns();
const EVENT_TYPE_PATTERN = /^on([A-Z]\w+$)/;
exports.EVENT_TYPE_PATTERN = EVENT_TYPE_PATTERN;
// 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) {
if (!target) throw TypeError("Event target must be an object");
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;
var onceWeakMap = new WeakMap();
/**
* 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) {
let replacement = function observer(...args) {
off(target, type, observer);
onceWeakMap.delete(listener);
listener.apply(target, args);
};
onceWeakMap.set(listener, replacement);
on(target, type, replacement);
}
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} args
* Arguments that will be passed to listeners.
*/
function emit (target, type, ...args) {
emitOnObject(target, type, target, ...args);
}
exports.emit = emit;
/**
* A variant of emit that allows setting the this property for event listeners
*/
function emitOnObject(target, type, thisArg, ...args) {
let all = observers(target, '*').length;
let state = observers(target, type);
let listeners = state.slice();
let count = listeners.length;
let index = 0;
// If error event and there are no handlers (explicit or catch-all)
// then print error message to the console.
if (count === 0 && type === 'error' && all === 0)
console.exception(args[0]);
while (index < count) {
try {
let listener = listeners[index];
// Dispatch only if listener is still registered.
if (~state.indexOf(listener))
listener.apply(thisArg, 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') emit(target, 'error', error);
else console.exception(error);
}
index++;
}
// Also emit on `"*"` so that one could listen for all events.
if (type !== '*') emit(target, '*', type, ...args);
}
exports.emitOnObject = emitOnObject;
/**
* 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) {
if (onceWeakMap.has(listener)) {
listener = onceWeakMap.get(listener);
onceWeakMap.delete(listener);
}
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(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;
/**
* Registers listeners on the given event `target` from the given `listeners`
* dictionary. Iterates over the listeners and if property name matches name
* pattern `onEventType` and property is a function, then registers it as
* an `eventType` listener on `target`.
*
* @param {Object} target
* The type of event.
* @param {Object} listeners
* Dictionary of listeners.
*/
function setListeners(target, listeners) {
Object.keys(listeners || {}).forEach(key => {
let match = EVENT_TYPE_PATTERN.exec(key);
let type = match && match[1].toLowerCase();
if (!type) return;
let listener = listeners[key];
if (typeof(listener) === 'function')
on(target, type, listener);
});
}
exports.setListeners = setListeners;
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