浅谈node的事件机制

var listeners = this.__events[key];
var len = listeners.length;

for (var i=0; i<len; i++) {
listeners[i].apply(this, arg)
}
return this

},
off: function(key, listener) {
if (!key && !listener) {
this.__events = {}
}
if (key && !listener) {
delete this.__events[key] }
if (key && listener) {
var listeners = this.__events[key];
var index = _indexOf(listeners, listener);
(index > -1) && listeners.splice(index, 1);
}
return this
}
}

var _indexOf = function(array,key){
if (array === null) return -1
var i = 0, length = array.length
for (; i < length; i++) if (array[i] === key) return i
return -1
}
//调用
Event.on('console1', function(num) {
console.log(num); // 1
});

Event.emit('console1', 1)

node的EventEmitter

node的EventEmitter基本逻辑和上面提供的例子基本一样，只是更加复杂些。

1.订阅事件on

function _addListener(target, type, listener, prepend) {
 var m;
 var events;
 var existing;
 if (typeof listener !== 'function')
  throw new TypeError('"listener" argument must be a function');
 events = target._events;
 ...
 if (typeof existing === 'function') {
   // Adding the second element, need to change to array.
   existing = events[type] =
    prepend ? [listener, existing] : [existing, listener];
  } else {
   // If we've already got an array, just append.
   if (prepend) {
    existing.unshift(listener);
   } else {
    existing.push(listener);
   }
  }
 return target;
}
EventEmitter.prototype.addListener = function addListener(type, listener) {
 return _addListener(this, type, listener, false);
};
EventEmitter.prototype.on = EventEmitter.prototype.addListener;

2.发布事件

EventEmitter.prototype.emit = function emit(type) {
 ...
 handler = events[type];
 switch (len) {
  // fast cases
  case 1:
   emitNone(handler, isFn, this);
   break;
  case 2:
   emitOne(handler, isFn, this, arguments[1]);
   break;
  case 3:
   emitTwo(handler, isFn, this, arguments[1], arguments[2]);
   break;
  case 4:
   emitThree(handler, isFn, this, arguments[1], arguments[2], arguments[3]);
   break;
  // slower
  default:
   args = new Array(len - 1);
   for (i = 1; i < len; i++)
    args[i - 1] = arguments[i];
   emitMany(handler, isFn, this, args);
 }
}

讲到这里，相信大家已经明白EventEmitter的实现思路。

参考资料

node events.js