node/lib/events.js

// Copyright Joyent, Inc. and other Node contributors.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to permit
// persons to whom the Software is furnished to do so, subject to the
// following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
// USE OR OTHER DEALINGS IN THE SOFTWARE.

var domain;

exports.usingDomains = false;

function EventEmitter() {
  this.domain = null;
  if (exports.usingDomains) {
    // if there is an active domain, then attach to it.
    domain = domain || require('domain');
    if (domain.active && !(this instanceof domain.Domain)) {
      this.domain = domain.active;
    }
  }
  this._events = this._events || {};
  this._maxListeners = this._maxListeners || defaultMaxListeners;
}
exports.EventEmitter = EventEmitter;

// By default EventEmitters will print a warning if more than
// 10 listeners are added to it. This is a useful default which
// helps finding memory leaks.
//
// Obviously not all Emitters should be limited to 10. This function allows
// that to be increased. Set to zero for unlimited.
var defaultMaxListeners = 10;
EventEmitter.prototype.setMaxListeners = function(n) {
  if (typeof n !== 'number' || n < 0)
    throw TypeError('n must be a positive number');
  this._maxListeners = n;
};

EventEmitter.prototype.emit = function(type) {
  var er, handler, len, args, i, listeners;

  if (!this._events)
    this._events = {};

  // If there is no 'error' event listener then throw.
  if (type === 'error') {
    if (!this._events.error ||
        (typeof this._events.error === 'object' &&
         !this._events.error.length)) {
      er = arguments[1];
      if (this.domain) {
        er.domainEmitter = this;
        er.domain = this.domain;
        er.domainThrown = false;
        this.domain.emit('error', er);
      } else if (er instanceof Error) {
        throw er; // Unhandled 'error' event
      } else {
        throw TypeError('Uncaught, unspecified "error" event.');
      }
      return false;
    }
  }

  handler = this._events[type];

  if (typeof handler === 'undefined')
    return false;

  if (this.domain && this !== process)
    this.domain.enter();

  if (typeof handler === 'function') {
    switch (arguments.length) {
      // fast cases
      case 1:
        handler.call(this);
        break;
      case 2:
        handler.call(this, arguments[1]);
        break;
      case 3:
        handler.call(this, arguments[1], arguments[2]);
        break;
      // slower
      default:
        len = arguments.length;
        args = new Array(len - 1);
        for (i = 1; i < len; i++)
          args[i - 1] = arguments[i];
        handler.apply(this, args);
    }
  } else if (typeof handler === 'object') {
    len = arguments.length;
    args = new Array(len - 1);
    for (i = 1; i < len; i++)
      args[i - 1] = arguments[i];

    listeners = handler.slice();
    len = listeners.length;
    for (i = 0; i < len; i++)
      listeners[i].apply(this, args);
  }

  if (this.domain && this !== process)
    this.domain.exit();

  return true;
};

EventEmitter.prototype.addListener = function(type, listener) {
  var m;

  if (typeof listener !== 'function')
    throw TypeError('listener must be a function');

  if (!this._events)
    this._events = {};

  // To avoid recursion in the case that type === "newListener"! Before
  // adding it to the listeners, first emit "newListener".
  if (this._events.newListener)
    this.emit('newListener', type, typeof listener.listener === 'function' ?
              listener.listener : listener);

  if (!this._events[type])
    // Optimize the case of one listener. Don't need the extra array object.
    this._events[type] = listener;
  else if (typeof this._events[type] === 'object')
    // If we've already got an array, just append.
    this._events[type].push(listener);
  else
    // Adding the second element, need to change to array.
    this._events[type] = [this._events[type], listener];

  // Check for listener leak
  if (typeof this._events[type] === 'object' && !this._events[type].warned) {
    m = this._maxListeners;
    if (m && m > 0 && this._events[type].length > m) {
      this._events[type].warned = true;
      console.error('(node) warning: possible EventEmitter memory ' +
                    'leak detected. %d listeners added. ' +
                    'Use emitter.setMaxListeners() to increase limit.',
                    this._events[type].length);
      console.trace();
    }
  }

  return this;
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

EventEmitter.prototype.once = function(type, listener) {
  if (typeof listener !== 'function')
    throw TypeError('listener must be a function');

  function g() {
    this.removeListener(type, g);
    listener.apply(this, arguments);
  }

  g.listener = listener;
  this.on(type, g);

  return this;
};

// emits a 'removeListener' event iff the listener was removed
EventEmitter.prototype.removeListener = function(type, listener) {
  var list, position, length, i;

  if (typeof listener !== 'function')
    throw TypeError('listener must be a function');

  if (!this._events || !this._events[type])
    return this;

  list = this._events[type];
  length = list.length;
  position = -1;

  if (list === listener ||
      (typeof list.listener === 'function' && list.listener === listener)) {
    this._events[type] = undefined;
    if (this._events.removeListener)
      this.emit('removeListener', type, listener);

  } else if (typeof list === 'object') {
    for (i = length; i-- > 0;) {
      if (list[i] === listener ||
          (list[i].listener && list[i].listener === listener)) {
        position = i;
        break;
      }
    }

    if (position < 0)
      return this;

    if (list.length === 1) {
      list.length = 0;
      this._events[type] = undefined;
    } else {
      list.splice(position, 1);
    }

    if (this._events.removeListener)
      this.emit('removeListener', type, listener);
  }

  return this;
};

EventEmitter.prototype.removeAllListeners = function(type) {
  var key, listeners;

  if (!this._events)
    return this;

  // not listening for removeListener, no need to emit
  if (!this._events.removeListener) {
    if (arguments.length === 0)
      this._events = {};
    else if (this._events[type])
      this._events[type] = undefined;
    return this;
  }

  // emit removeListener for all listeners on all events
  if (arguments.length === 0) {
    for (key in this._events) {
      if (key === 'removeListener') continue;
      this.removeAllListeners(key);
    }
    this.removeAllListeners('removeListener');
    this._events = {};
    return this;
  }

  listeners = this._events[type];

  if (typeof listeners === 'function') {
    this.removeListener(type, listeners);
  } else {
    // LIFO order
    while (listeners.length)
      this.removeListener(type, listeners[listeners.length - 1]);
  }
  this._events[type] = undefined;

  return this;
};

EventEmitter.prototype.listeners = function(type) {
  var ret;
  if (!this._events || !this._events[type])
    ret = [];
  else if (typeof this._events[type] === 'function')
    ret = [this._events[type]];
  else
    ret = this._events[type].slice();
  return ret;
};

EventEmitter.listenerCount = function(emitter, type) {
  var ret;
  if (!emitter._events || !emitter._events[type])
    ret = 0;
  else if (typeof emitter._events[type] === 'function')
    ret = 1;
  else
    ret = emitter._events[type].length;
  return ret;
};