ExpressJS : Strange String Comparation

I'm doing this:

res.jsonp({
     userId:  user._id,
     spotUserId:  spot.user._id, 
     condition:  (user._id === spot.user._id)
});

And the result is this:

{
    "userId": "551192836bff030fb657777c",
    "spotUserId": "551192836bff030fb657777c",
    "condition": false
}

I don't understand why the condition is false... Help me!