经典JS

用apply把document当作this传入getId函数，帮助“修正”this;

document.getElementById = (function (func) {
    return function () {
        return func.apply(document, arguments);
    }
})(document.getElementById);

//调用
var getId = document.getElementById;
var div = getId('div2');

类型判断

var Type = {};

for (var i = 0, type; type = ['String', 'Array', 'Number'][i++];) {

    (function (type) {
        Type['is' + type] = function (obj) {
            return Object.prototype.toString.call(obj) === '[object ' + type + ']';
        }
    })(type);

};

自定义事件（一）：

var Event = {
    _listeners: {},    
    // 添加
    addEvent: function(type, fn) {
        if (typeof this._listeners[type] === "undefined") {
            this._listeners[type] = [];
        }
        if (typeof fn === "function") {
            this._listeners[type].push(fn);
        }    
        return this;
    },
    // 触发
    fireEvent: function(type) {
        var arrayEvent = this._listeners[type];
        if (arrayEvent instanceof Array) {
            for (var i=0, length=arrayEvent.length; i<length; i+=1) {
                if (typeof arrayEvent[i] === "function") {
                    arrayEvent[i]({ type: type });    
                }
            }
        }    
        return this;
    },
    // 删除
    removeEvent: function(type, fn) {
        var arrayEvent = this._listeners[type];
        if (typeof type === "string" && arrayEvent instanceof Array) {
            if (typeof fn === "function") {
                // 清除当前type类型事件下对应fn方法
                for (var i=0, length=arrayEvent.length; i<length; i+=1){
                    if (arrayEvent[i] === fn){
                        this._listeners[type].splice(i, 1);
                        break;
                    }
                }
            } else {
                // 如果仅仅参数type, 或参数fn邪魔外道，则所有type类型事件清除
                delete this._listeners[type];
            }
        }
        return this;
    }
};

自定义事件（二）：

//自定义事件

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;
             };
             //添加监听事件，并缓存
             _listen = function (key,fn,cache) { 
                 if(!cache[key]){
                     cache[key]=[];
                 }
                 cache[key].push(fn);
              };
              //移除监听
              _remove=function (key,cache,fn) { 
                  if(cache[key]){ //如果存在该监听事件
                      if(fn){ //如果存在回调函数
                          for (var i = cache[key].length; i >=0; i--){
                             if(cache[key][i]===fn){
                                 cache[key].splice(i,1); //移除此回调函数
                             }
                          }
                      }else{
                          cache[key]=[]; //清除此事件（为什么存在回调函数时不执行此步骤，奇怪）
                      }
                  }
               };

               //触发事件
               _trigger=function () { 
                   var cache = _shift.call(arguments), //第一个参数是cache
                       key = _shift.call(arguments),  //第二个参数是key
                       args = arguments,
                       _self = this,
                       ret,
                       stack= cache[key];

                    if(!stack || !stack.length){ //没有回调函数则直接返回
                        return;
                    }

                    return each(stack, function () { //执行所有的回调函数
                        return this.apply(_self,args);
                     });

                };
                //创建事件的实例
                _create=function (namespace) { 
                    var namespace = namespace || _default;
                    var cache ={},
                        offlineStack=[], //离线事件
                        ret={
                            listen:function (key,fn,last) { 
                                _listen(key,fn,cache);
                                if(offlineStack===null){
                                    return;
                                }
                                if(last==='last'){
                                    offlineStack.length && offlineStack.pop()(); //如果是最后一个离线事件，触发此离线事件并移除此事件
                                }else{
                                    each(offlineStack,function(){ //如果是多个离线事件，并遍历触发
                                        this();
                                    });
                                }

                                offlineStack = null; 清空离线事件
                             },
                             //执行一次监听事件
                             one:function (key,fn,last) { 
                                 _remove(key,cache); //此缓存中移除此事件
                                 this.listen(key,fn,last); //添加此事件
                              },
                              remove:function (key,fn) { 
                                  _remove(key,cache,fn);
                               },
                               trigger:function () { 
                                   var fn,
                                       args,
                                       _self=this;

                                    _unshift.call(arguments,cache); //将cache缓存添加到arguments参数集合中
                                    args=arguments;
                                    fn=function(){
                                        return _trigger.apply(_self,args);
                                    };

                                    if(offlineStack){
                                        return offlineStack.push(fn);
                                    }
                                    return fn(); //触发事件
                                }

                        };

                        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;

 })();

方法绑定：

Function.prototype.bind = function () {
    var self = this,
    context  = [].shift.call(arguments),
    args     = [].slice.call(arguments);
    
    return function () {
        return self.apply( context, [].concat.call(args, [].slice.call(arguments)) )
    } 
}

AOP：

Function.prototype.before = function(beforefn) {
    var _self = this;
    return function() {
        beforefn.apply(this, arguments);
        return _self.apply(this, arguments);
    }
}

Function.prototype.after = function(afterfn) {
    var _self = this;
    return function() {
        var ret = _self.apply(this, arguments);
        afterfn.apply(this, arguments);
        return ret;
    }
}