1
  2/**
  3 * Expose `Emitter`.
  4 */
  5
  6module.exports = Emitter;
  7
  8/**
  9 * Initialize a new `Emitter`.
 10 *
 11 * @api public
 12 */
 13
 14function Emitter(obj) {
 15  if (obj) return mixin(obj);
 16};
 17
 18/**
 19 * Mixin the emitter properties.
 20 *
 21 * @param {Object} obj
 22 * @return {Object}
 23 * @api private
 24 */
 25
 26function mixin(obj) {
 27  for (var key in Emitter.prototype) {
 28    obj[key] = Emitter.prototype[key];
 29  }
 30  return obj;
 31}
 32
 33/**
 34 * Listen on the given `event` with `fn`.
 35 *
 36 * @param {String} event
 37 * @param {Function} fn
 38 * @return {Emitter}
 39 * @api public
 40 */
 41
 42Emitter.prototype.on =
 43Emitter.prototype.addEventListener = function(event, fn){
 44  this._callbacks = this._callbacks || {};
 45  (this._callbacks[event] = this._callbacks[event] || [])
 46    .push(fn);
 47  return this;
 48};
 49
 50/**
 51 * Adds an `event` listener that will be invoked a single
 52 * time then automatically removed.
 53 *
 54 * @param {String} event
 55 * @param {Function} fn
 56 * @return {Emitter}
 57 * @api public
 58 */
 59
 60Emitter.prototype.once = function(event, fn){
 61  var self = this;
 62  this._callbacks = this._callbacks || {};
 63
 64  function on() {
 65    self.off(event, on);
 66    fn.apply(this, arguments);
 67  }
 68
 69  on.fn = fn;
 70  this.on(event, on);
 71  return this;
 72};
 73
 74/**
 75 * Remove the given callback for `event` or all
 76 * registered callbacks.
 77 *
 78 * @param {String} event
 79 * @param {Function} fn
 80 * @return {Emitter}
 81 * @api public
 82 */
 83
 84Emitter.prototype.off =
 85Emitter.prototype.removeListener =
 86Emitter.prototype.removeAllListeners =
 87Emitter.prototype.removeEventListener = function(event, fn){
 88  this._callbacks = this._callbacks || {};
 89
 90  // all
 91  if (0 == arguments.length) {
 92    this._callbacks = {};
 93    return this;
 94  }
 95
 96  // specific event
 97  var callbacks = this._callbacks[event];
 98  if (!callbacks) return this;
 99
100  // remove all handlers
101  if (1 == arguments.length) {
102    delete this._callbacks[event];
103    return this;
104  }
105
106  // remove specific handler
107  var cb;
108  for (var i = 0; i < callbacks.length; i++) {
109    cb = callbacks[i];
110    if (cb === fn || cb.fn === fn) {
111      callbacks.splice(i, 1);
112      break;
113    }
114  }
115  return this;
116};
117
118/**
119 * Emit `event` with the given args.
120 *
121 * @param {String} event
122 * @param {Mixed} ...
123 * @return {Emitter}
124 */
125
126Emitter.prototype.emit = function(event){
127  this._callbacks = this._callbacks || {};
128  var args = [].slice.call(arguments, 1)
129    , callbacks = this._callbacks[event];
130
131  if (callbacks) {
132    callbacks = callbacks.slice(0);
133    for (var i = 0, len = callbacks.length; i < len; ++i) {
134      callbacks[i].apply(this, args);
135    }
136  }
137
138  return this;
139};
140
141/**
142 * Return array of callbacks for `event`.
143 *
144 * @param {String} event
145 * @return {Array}
146 * @api public
147 */
148
149Emitter.prototype.listeners = function(event){
150  this._callbacks = this._callbacks || {};
151  return this._callbacks[event] || [];
152};
153
154/**
155 * Check if this emitter has `event` handlers.
156 *
157 * @param {String} event
158 * @return {Boolean}
159 * @api public
160 */
161
162Emitter.prototype.hasListeners = function(event){
163  return !! this.listeners(event).length;
164};