Return value from Object match

Question

I'm, by no means, JS fluent, so forgive me if im asking for some really basic stuff, but I've not being able to find a proper answer to my question.

Im writting my first Node.js (plus Extra Framework and Socket.io) app and Im having some fun setting up the server side of a FB-like messenger (surprise!!!).

So, let's say I have this data structure to store online users(This is a JSON Array, but I'm not sure it is the best way to do it or should I go with Javascript Objects):

[
  {
    "site": 45,
    "users": [
        {
            "idUser": 5,
            "idSocket": "qwe87r7w8qwe",
            "name": "Carlos Ray Norris"
        },
        {
            "idUser": 6,
            "idSocket": "v8d9d0fgfs7d",
            "name": "John Connor"
        }
    ]
},
{
    "site": 48,
    "users": [
          {
            "idUser": 22,
            "idSocket": "qwe87r7w8qwe",
            "name": "David Bowie"
          },
          {
            "idUser": 23,
            "idSocket": "v8d9d0fgfs7d",
            "name": "Barack H. Obama"
          }
      ]
  }
]

What I want to do is to search in the array for x value given y. In this case, retrieving the idSocket knowing the idUser WITHOUT having to run through the array values.

So I have basically 2 questions: first, what would be the proper way to store users online? and secondly, how to find values matching with the values I already know (find the idSocket that has a given idUser).

I would like a pure JS approach(or using some of the tools given by Node, Socket.io or Express), but if that's not possible then I can look for some JQuery.

EDIT I took chovy's advice and modified a little the structure, now it looks like this

{
  45: { // site
    05: { // userId
        "name": "Carlos Ray Norris",
        "socketID": "qwe87r7w8qwe"
    },
    06: {
        "name": "John Connor",
        "socketID": "v8d9d0fgfs7d"
    }
},
48: {
    22: {
        "name": "David Bowie",
        "socketID": "erv7e6v876vr"
    },
    23: {
        "name": "Barack H. Obama",
        "socketID": "brt877brtt87"
    }
  }
}

Thanks to Node.js, I can easily access to the data like this (I know both, the site and userId value) var socket = data[site]["05"].socketId . Im guessing this is done thanks to Node.js, but Im not completely sure.

Answer 1

Build a lookup table: An JS object as a key-value-map, where the keys are the ids and the values are the user objects. Then you can select/match an user by id in O(n) .

var map = {};
for (var i=0; i<arr.length; i++) {
    var site = arr[i].site,
        users = arr[i].users;
    for (var j=0; j<users.length; j++) {
        users[i].site = site; // needed for finding a user's site
        map[ users[i].idUser ] = users[i];
    }
}

// Now,
> map[ 23 ] 
{idUser:23, idSocket:"v8d9d0fgfs7d", name:"Barack H. Obama", site:48}

Answer 2

Can you structure your data so the user id is the key, instead of an array you have to loop over?

var data = {
 45: { user: 'Fred' },
 58: { user: 'Sam' )
};


var userId = 45;
data[userId].user // => 'Fred'