Павел Воронин

var objects = [
    {
        "id": "34bfd2234234177b17854d52",
        "name": "Miki",
        "lastname": "Adams",
        "profession": "Designer",
        "email": "mmm@gmail.com",
        "online": true,
        "admin": false,
        "createdAt": "Wed Jan 21 2015 19: 24: 56 GMT + 0300(MSK)",
        "updatedAt": "Thu Jan 22 2015 17: 22: 47 GMT + 0300(MSK)",
        "avatar": ""
    },
    {
        "id": "54bfd2d81b9b177b17854d52",
        "name": "Artur",
        "lastname": "Altman",
        "profession": "Designer",
        "email": "aaa@gmail.com",
        "online": true,
        "admin": false,
        "createdAt": "Wed Jan 21 2015 19: 24: 56 GMT + 0300(MSK)",
        "updatedAt": "Thu Jan 22 2015 17: 22: 47 GMT + 0300(MSK)",
        "avatar": ""
    }
];

Array.prototype.containsObjectWithId = function(id){
    return !!this.filter(function(el){
        return el.hasOwnProperty('id') && el.id == id
    }).length;
}

console.log(objects.containsObjectWithId('54bfd2d81b9b177b17854d52')) // true
console.log(objects.containsObjectWithId('ok, this id do not exist')) // false