>You had to take time to look up operator-in because you're not used to using operator-in

I'm using in (`if('age' in value)`), but not for..in. There's a difference. I don't need to use that (you didn't in your example, even though you should have), but then my code would blow up in many of the same cases as yours will.

Anyway, what's wrong with that code is you'll need a hasOwnProperty check, you'll need to break out of the loop when done, it blows up if 'age' isn't a property on one of the objects in the object, it blows up if one of the properties of obj isn't an object, it blows up if obj is null/undefined, and it will deoptimize the entire function it's in in most cases in V8.

To at least fix the bugs that yours has that mine didn't, your code should be:

    for (var key in obj) {
      if (obj.hasOwnProperty(key)) {
        var val = obj[key]
        if ('age' in val && val.age === 1) {
          // there you go
        }
      }
    }

but again that still needs some undefined/null guards at a few spots, and it needs to be able to handle both an array and an obj at where obj is to really be an equivalent of what i was using _.filter for.

>You default assume other people's code is better than yours.

No, I know the lodash code i'm using is better than mine because i've looked at it, i've looked at it's test coverage, i've looked at it's performance numbers, and i've looked at it's usage.

Also... >I skipped over it because it's a solution in search of a problem.

Then why did you skip this part in my last comment:

>it's disingenuous at best and borderline lying to say that lodash is 500kb. The DEVELOPER version is 500kb, the production version is 67kb before gzipping, and 22kb after gzipping

You made me curious, so i actually took a look at my current in-development app i'm writing that i include lodash. The grand total from all lodash functions is 22k un-gzipped, and 7k gzipped.

For that i've significantly reduced my code complexity, increased compatibility, reduced the amount of tests i needed to run and maintain, and improved performance in one pretty out-there edge case.

You don't need to use lodash, and in many cases you shouldn't. But don't act like your applications are better than others in any way because you aren't using lodash.