Question

Using Javascript I want to have a JSON or array that will store id & ip data pairs, such that if I want the ip of a particular id=123, I can easily get it, ie by using data[123] or data['123']['ip'].

I tried this but cant seem to select the ip based on id:

var connected_clients = {
    "clients": [{id: "12345", ip: "123.123.123.123"}]
};

Also tried using this below, but I cant seem to add new id/ip pairs to it…

var connected_clients = {
    "12345": {
        id: "12345",
        ip: "123.123.123.123"
    }
};

How should it be done?

Answer 1

(First up, you don’t have “a JSON”, you have an object. JSON is a string representation of data – or you could think of it as an object serialised to string form. Anyway…)

If you want to be able to look up the details for a known id, your second structure will work fine.

With more clients it would look like this:

var connected_clients = {
    "12345": {
        id: "12345",
        ip: "123.123.123.123"
    },
    "12346": {
        id: "12346",
        ip: "123.234.345.456"
    },
    "12347": {
        id: "12347",
        ip: "555.444.333.222"
    }
};

And you’d get the ip of client “12346” like this:

connected_clients["12346"]["ip"]
// OR
connected_clients["12346"].ip
// OR if the id was in a variable
var currentId = "12346";
connected_clients[currentId]["ip"]

If you want to add a client:

connected_clients[newId] = { id: newId, ip : someIp };

If you want to check if a particular id already exists:

if (connected_clients.hasOwnProperty(someId)) {
   // do something
}
// OR use 'in' since your object doesn't really have a prototype chain to worry about
if (someId in connected_clients) {
   // do something
}

To iterate through all the clients:

for (var key in connected_clients) {
   console.log(key + " - ip is " + connected_clients[key]["ip"]);
}

Further reading:

• https://developer.mozilla.org/en/JavaScript/Guide/Working_with_Objects
• https://developer.mozilla.org/en/JavaScript/Reference/Statements/for…in