document.body.addEventListener("click", function() {
 console.log(1);
}, false);

// 可以多個訂閱者
document.body.addEventListener("click", function() {
 console.log(2);
}, false);

doucment.body.click();

某網站有header頭部、nav導航、消息列表等模塊。這幾個模塊的渲染都需要獲取用戶登陸信息。

（1）一般寫法：

$.ajax({
 url: './login',
 type: 'post',
 contentType: 'application/json',
 dataType:'json',
 success: function(data) {
 if(data.status === "success") {
  // 登錄成功，渲染header、nav
  header.setInfo(data.headerInfo);
  nav.setInfo(data.navInfo);
 }
 }
});

（2）使用觀察者模式，很輕松解耦！

$.ajax({
 ...,
 success: function(data) {
 if(data.status === "success") {
  // 登錄成功，發(fā)布登陸成功消息
  login.trigger("loginsuccess", data);
 }
 }
});

var header = (function() {
 // 監(jiān)聽消息
 login.listen("loginsuccess", function(data){
 header.setInfo(data.headerInfo);
 });
 return {
 setInfo: function(data) {
  console.log("設置header信息");
 }
 };
})();

var nav = (function() {
 login.listen("loginsuccess", function(data){
 nav.setInfo(data.navInfo);
 });
 return {
 setInfo: function(data) {
  console.log("設置nav信息");
 }
 }
})();

三、通用觀察者模式

/*
 * 示例：
 * Event.create("namespace1").listen('click', function(a){
 * console.log(a);
 * });
 * Event.create("namespace1").trigger("click", 1);
 */
var Event = (function() {
 var global = this,
 Event,
 _default = 'default';

 Event = function() {
 var _listen,
  _trigger,
  _remove,
  _slice = Array.prototype.slice,
  _shift = Array.prototype.shift,
  _unshift = Array.prototype.unshift,
  namespaceCache = [],
  _create,
  find,
  each = function( ary, fn) {
  var ret;
  for(var i = 0, l = ary.length; i < l; i++) {
   var n = ary[i];
   ret = fn.call(n, i, n);
  }
  return ret;
  };
 // 訂閱
 _listen = function(key, fn, cache) {
  if(!cache[key]) {
  cache[key] = [];
  }
  cache[key].push(fn);
 };
 // 移除訂閱
 _remove = function(key, cache, fn) {
  if(cache[key]) {
  if(fn) {
   for(var i = cache[key].length; i >=0; i++) {
   if(cache[key][i] === fn) {
    cache[key].splice(i, 1);
   }
   }
  }else {
   cache[key] = [];
  }
  }
 };
 // 發(fā)布
 _trigger = function() {
  var cache = _shift.call(arguments),
  key = _shift.call(arguments),
  args = arguments,
  _self = this,
  ret,
  stack = cache[key];
  if(!stack || !stack.length) {
  return;
  }
  return each(stack, function() {
  return this.apply(_self, args);
  });
 };
 // 創(chuàng)建命名空間
 _create = function(namespace) {
  var namespace = namespace || _default;
  var cache = {},
  offlineStack = [], // 離線事件
  ret = {
   listen: function (key, fn, last) {
   _listen(key, fn, cache);
   if (offlineStack == null) {
    return;
   }
   if (last === 'last') {
    offlineStack.length && offlineStack.pop()();
   } else {
    each(offlineStack, function () {
    this();
    });
   }
   offlineStack = null;
   },

   one: function (key, fn, last) {
   _remove(key, cache);
   this.listen(key, fn, last);
   },

   remove: function(key, fn, last) {
   _remove(key, cache, fn);
   },

   trigger: function() {
   var fn,
    args,
    _self = this;
   _unshift.call(arguments, cache);
   args = arguments;
   fn = function() {
    return _trigger.apply(_self, args);
   };
   if(offlineStack) {
    return offlineStack.push(fn);
   }
   return fn;
   }
  };

  return namespace ? (namespaceCache[namespace] ? namespaceCache[namespace] : namespaceCache[namespace] = ret) : ret;
  };

 return {
  create: _create,
  one: function(key, fn, last) {
  var event = this.create();
  event.one(key, fn, last);
  },
  remove: function(key, fn) {
  var event = this.create();
  event.remove(key, fn);
  },
  listen: function(key, fn, last) {
  var event = this.create();
  event.listen(key, fn, last);
  },
  trigger: function() {
  var event = this.create();
  event.trigger.apply(this, arguments);
  }
 };
 }();
 return Event;
})();

希望本文所述對大家學習javascript程序設計有所幫助。

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