[{a:1000,b: 10},{a:1000,b:11},{a:10001,b:10}]
把数组对象里面的a属性值相同的b属性累加
得到这样的结果：
[{a:1000,b:21},{a:10001,b:10}]

obj_merge(obj){
     var obj1 = {};
     if(Object.prototype.toString.call(obj) != '[object Array]'){
        return obj;
     }
     var obj2 = new Array(); 
     obj.map(function(x){
        var temp =x.a;
        if(temp in obj1){
            var sum = obj1[temp].b*1+x.b*1;
            obj1[temp]={a:temp,b:sum}
            
        }else{
            obj1[temp]={a:temp,b:x.b}
        }
     })  
     for(i in obj1){
        obj2.push(obj1[i]);
     }
     return obj2;
}