javascript 异步队列

(function(win, undefined){
    var asycs = win.as = function(ischain){
        var me = this;
        me.ischain = ischain || false;
        if(!(this instanceof as)){
            return new asycs(ischain);
        }
    }
    
    asycs.prototype.add = function(){//主入口
        var arg = Array.prototype.slice.call(arguments),
            me = this;
        me.array = arg;
        me.i = 0;
        me.reFunc();

    }

    asycs.prototype._listener = function(order){
        var me = this;
        if(--me.length=== 0){
            me.callback();
        }
    }

    asycs.prototype.customShift = function(callback){
        var me = this;
        return function(order){
            return callback(function(){
                return me.giveMessage(order);
            })
        }
    }

    asycs.prototype.reFunc = function(){
        var me = this,i = 0 ;
        
        var len  = me.array.length;
            me.length = len - 1;
            me.callback = me.array[len-1];
        while(i < len - 1){
            
            var func = me.array[i];
            me.array[i] = me.customShift(func);
            if(!me.ischain){
                me.array[i](i);
            }
            i++;
        }
        
        if(me.ischain){
            me.array[0](0);
        }

        return len;
    }

    asycs.prototype.giveMessage = function(order){
        var me = this;
        me._listener(order);
        if(me.ischain){
            if(++order < me.array.length - 1){
                me.array[order](order);
            }
        }
        return {
            rec : me.i++,
            total : "ok"
        }
    }

})(window, undefined)

根据ischain true a执行完执行b b执行完执行c 全部执行完 执行最后一个函数

false a b c 异步没顺序 但是最后一个函数要等他们执行完再去执行

每执行完一个函数会通知asycs对象 对象接收到后判断是否数组中的最后一个 来执行 回调