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 isArray = Array.isArray;
var domain;

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 || null;
  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) {
  this._maxListeners = n;
};

// non-global reference, for speed.
var PROCESS;

EventEmitter.prototype.emit = function(type) {
  // If there is no 'error' event listener then throw.
  if (type === 'error') {
    if (!this._events || !this._events.error ||
        (isArray(this._events.error) && !this._events.error.length))
    {
      if (this.domain) {
        var er = arguments[1];
        er.domain_emitter = this;
        er.domain = this.domain;
        er.domain_thrown = false;
        this.domain.emit('error', er);
        return false;
      }

      if (arguments[1] instanceof Error) {
        throw arguments[1]; // Unhandled 'error' event
      } else {
        throw new Error("Uncaught, unspecified 'error' event.");
      }
      return false;
    }
  }

  if (!this._events) return false;
  var handler = this._events[type];
  if (!handler) return false;

  if (typeof handler == 'function') {
    if (this.domain) {
      PROCESS = PROCESS || process;
      if (this !== PROCESS) {
        this.domain.enter();
      }
    }
    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:
        var l = arguments.length;
        var args = new Array(l - 1);
        for (var i = 1; i < l; i++) args[i - 1] = arguments[i];
        handler.apply(this, args);
    }
    if (this.domain && this !== PROCESS) {
      this.domain.exit();
    }
    return true;

  } else if (isArray(handler)) {
    if (this.domain) {
      PROCESS = PROCESS || process;
      if (this !== PROCESS) {
        this.domain.enter();
      }
    }
    var l = arguments.length;
    var args = new Array(l - 1);
    for (var i = 1; i < l; i++) args[i - 1] = arguments[i];

    var listeners = handler.slice();
    for (var i = 0, l = listeners.length; i < l; i++) {
      listeners[i].apply(this, args);
    }
    if (this.domain && this !== PROCESS) {
      this.domain.exit();
    }
    return true;

  } else {
    return false;
  }
};

EventEmitter.prototype.addListener = function(type, listener) {
  if ('function' !== typeof listener) {
    throw new Error('addListener only takes instances of 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 (isArray(this._events[type])) {

    // 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 (isArray(this._events[type]) && !this._events[type].warned) {
    var m;
    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 ('function' !== typeof listener) {
    throw new Error('.once only takes instances of Function');
  }

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

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

  return this;
};

// emits a 'removeListener' event iff the listener was removed
EventEmitter.prototype.removeListener = function(type, listener) {
  if ('function' !== typeof listener) {
    throw new Error('removeListener only takes instances of Function');
  }

  // does not use listeners(), so no side effect of creating _events[type]
  if (!this._events || !this._events[type]) return this;

  var list = this._events[type];

  if (isArray(list)) {
    var position = -1;
    for (var i = 0, length = list.length; i < length; i++) {
      if (list[i] === listener ||
          (list[i].listener && list[i].listener === listener))
      {
        position = i;
        break;
      }
    }

    if (position < 0) return this;
    list.splice(position, 1);
    if (list.length == 0)
      this._events[type] = null;

    if (this._events.removeListener) {
      this.emit('removeListener', type, listener);
    }
  } else if (list === listener ||
             (list.listener && list.listener === listener))
  {
    this._events[type] = null;

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

  return this;
};

EventEmitter.prototype.removeAllListeners = function(type) {
  if (!this._events) return this;

  // fast path
  if (!this._events.removeListener) {
    if (arguments.length === 0) {
      this._events = {};
    } else if (type && this._events && this._events[type]) {
      this._events[type] = null;
    }
    return this;
  }

  // slow(ish) path, emit 'removeListener' events for all removals
  if (arguments.length === 0) {
    for (var key in this._events) {
      if (key === 'removeListener') continue;
      this.removeAllListeners(key);
    }
    this.removeAllListeners('removeListener');
    this._events = {};
    return this;
  }

  var listeners = this._events[type];
  if (isArray(listeners)) {
    while (listeners.length) {
      // LIFO order
      this.removeListener(type, listeners[listeners.length - 1]);
    }
  } else if (listeners) {
    this.removeListener(type, listeners);
  }
  this._events[type] = null;

  return this;
};

EventEmitter.prototype.listeners = function(type) {
  if (!this._events || !this._events[type]) return [];
  if (!isArray(this._events[type])) {
    return [this._events[type]];
  }
  return this._events[type].slice(0);
};