'关联数组'/对象的Javascript'First或Default'函数

Question

Is there a better way to do this?

I'm storing values in what some would erroneously call an associated array:

The tokens object stores.... tokens and a count of documents using that token on a per-db level.

var tokens = {'db1' : { '654321': { 'docCount': 1 },
                        '321456': { 'docCount': 2 } },
              'db2' : { '999999': { 'docCount': 1 } } };

I can add/remove dbs and tokens and update the docCounts appropriately. We can assume, due to code omitted for brevity, that if a db exists, a token also exists with a docCount of at least 1.

If a db exists and I need to retrieve ANY of its tokens, what is the best method? If the dbs held arrays, it would be as easy as tokens['db1'][0] ... but I'm not using arrays.

I have something like the following, "inspired" by LINQ (please don't blame LINQ):

// NOTE: default not implemented here
var firstOrDefault = function(obj) {
  var thing;
  for (var i in obj) {
    thing = i;
    break;
  }
  return thing;
};

which would be called as so (simplified for example):

var anyToken;
if (tokens['db1') { anyToken = firstOrDefault(tokens['db1']); }

Generally returning per the above example '654321' (as this is an object, not an array, order is not guaranteed, but either value is acceptable in my code).

• Is this a reasonable method to get any value?
• Is there a better method?
• Should I just suck it up, shove everything into an array, and wrap the storage features that way?

---

UPDATE: I've removed the default reference, as an unfound item will a perfectly acceptable undefined response:

// NOTE: obj.hasOwnProperty not implemented for brevity
var firstOrAny = function(obj) {
  var thing;
  for (var i in obj) {
    thing = i;
    break;
  }
  return thing;
};

which would be called as so (simplified for example):

var anyToken;
if (tokens['db1') { anyToken = firstOrAny(tokens['db1']); }

Answer 1

Slightly shorter solution:

var firstOrDefault = function(obj, d) { 
  for (var i in obj)
  {
    if (obj.hasOwnProperty(i))
    {
      return obj[i];
    }
  }
  return d; 
};

But yes, it is the fastest way to get any (usually first inserted) key from an object.

I also added a hasOwnProperty check to prevent cases where the values are retrieved from the prototype chain.