兩個數組比較的問題，並從爲數組a添加數據b的屬性

數組a：
[
{"user_num":"75925","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75921","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"7595","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75984","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"759020","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75930","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75911","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75931","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75912","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75932","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75913","MeterNo":"50005445","BookNo":"51010"}
]

數組b:
[

                            {user_num:75925,name:"範小明"},
                            {user_num:75921,name:"李大霄"},
                            {user_num:7595,name:"劉士雨"},
                            {user_num:75984,name:"廖冰"},
                            {user_num:7598020,name:"李剛"},
                            {user_num:7597,name:"李世民"},
                            {user_num:75930,name:"劉彬彬"},
                            {user_num:75911,name:"森美"}
]

我想得到這樣的效果，遍歷數組a的user_num，如果，其值在數組b裏，則取出該數組b的name屬性，並添加到數組a中。如果user_num沒有在數組b中，在添加一個默認值name屬性(可以設爲default)給數組a.

最後，數組a將變成這樣：
[
{"user_num":"75925","MeterNo":"50005445","BookNo":"51010","name":"範小明"},
{"user_num":"75921","MeterNo":"50005445","BookNo":"51010","name":"李大霄"},
{"user_num":"7595","MeterNo":"50005445","BookNo":"51010","name":"劉士雨"},
{"user_num":"75984","MeterNo":"50005445","BookNo":"51010","name":"廖冰"},
{"user_num":"759020","MeterNo":"50005445","BookNo":"51010","name":"李剛"},
{"user_num":"75930","MeterNo":"50005445","BookNo":"51010","name":"劉彬彬"},
{"user_num":"75911","MeterNo":"50005445","BookNo":"51010","name":"森美"},
{"user_num":"75931","MeterNo":"50005445","BookNo":"51010","name":"default"},
{"user_num":"75912","MeterNo":"50005445","BookNo":"51010","name":"default"},
{"user_num":"75932","MeterNo":"50005445","BookNo":"51010","name":"default"},
{"user_num":"75913","MeterNo":"50005445","BookNo":"51010","name":"default"}

]

解決方法：

var a = [
{"user_num":"75925","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75921","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"7595","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75984","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"759020","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75930","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75911","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75931","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75912","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75932","MeterNo":"50005445","BookNo":"51010"},
{"user_num":"75913","MeterNo":"50005445","BookNo":"51010"}
]
var b = [
 
                            {user_num:75925,name:"範小明"},
                            {user_num:75921,name:"李大霄"},
                            {user_num:7595,name:"劉士雨"},
                            {user_num:75984,name:"廖冰"},
                            {user_num:7598020,name:"李剛"},
                            {user_num:7597,name:"李世民"},
                            {user_num:75930,name:"劉彬彬"},
                            {user_num:75911,name:"森美"}
];
for(var i=0;i<a.length;i++){
    var isIn = false;
    for(var j=0;j<b.length;j++){
        if(a[i].user_num == b[j].user_num){
            isIn = true;
            a[i].name = b[j].name;
            break;
        }
    }
    if(!isIn){
        a[i].name = 'default';
    }
}
console.log(a)