javascript - _.pluck 是否保留了 "plucked"数组的原始索引？

Question

我有一个 mongoDB 文档，其中包含一个对象字段数组，如下所示:

"leaving_users" : [
        {
            "user_id" : "FZ78Pr82JPz66Gc3p",
            "leaving_date" : ISODate("2015-06-12T14:14:14.501Z")
        }
    ]

我可以使用 _.pluck 获取与特定 user_id 相关的 leaving_date 吗？

我的代码似乎工作正常，但我想检查这是正确的方法，并确保如果我使用 _.pluck函数。

这是我的代码:

if (doc.leaving_users //guarding
    //if the user belongs to the leaving_users object array
    &&  _.pluck(doc.leaving_users, "user_id").indexOf(userId) != -1 
    //if his leaving_date field is after yesterday
    && doc.leaving_users[_.pluck(doc.leaving_users, "user_id").indexOf(userId)].leaving_date > yesterday)
                {
                    leftRecently  = true;
                }   else{
                    leftRecently  = false;
                }

额外的问题:如何让它更优雅？

Answer 1

是的，索引将是相同的。如果你看一下 the implementation of _.pluck 就很清楚了:

_.pluck = function(obj, key) {
  return _.map(obj, _.property(key));
};

...和the implementation of _.map :

_.map = _.collect = function(obj, iteratee, context) {
  iteratee = cb(iteratee, context);
  var keys = !isArrayLike(obj) && _.keys(obj),
      length = (keys || obj).length,
      results = Array(length);
  for (var index = 0; index < length; index++) {
    var currentKey = keys ? keys[index] : index;
    results[index] = iteratee(obj[currentKey], currentKey, obj);
  }
  return results;
};

---

就是说，我不会那样调用 _.pluck 两次，而且我认为我根本不会为此使用 _.pluck，我会用_.findIndex并保存结果:

var index;
if (doc.leaving_users //guarding
    //if the user belongs to the leaving_users object array
    && (index = _.findIndex(doc.leaving_users, function(e) { e.user_id === userId; }) !== -1)
    //if his leaving_date field is after yesterday
    && doc.leaving_users[index].leaving_date > yesterday)
                {
                    leftRecently  = true;
                }   else{
                    leftRecently  = false;
                }