Vérifiez si un élément d'un objet existe

Bonjour j'ai une question pour un de mes codes :) J'apprend sur le site du FreeCodeCamp et je souhaite pouvoir vérifier si un objet existe dans un de mes tableau ( des objets dans des tableaux ) j'ai trouver comment parcourir le tableaux mais pas comment vérifier l'existence d'un objet et ce qu'il y a dedans ...

Le code :

//Setup
var contacts = [
    {
        "firstName": "Akira",
        "lastName": "Laine",
        "number": "0543236543",
        "likes": ["Pizza", "Coding", "Brownie Points"]
    },
    {
        "firstName": "Harry",
        "lastName": "Potter",
        "number": "0994372684",
        "likes": ["Hogwarts", "Magic", "Hagrid"]
    },
    {
        "firstName": "Sherlock",
        "lastName": "Holmes",
        "number": "0487345643",
        "likes": ["Intriguing Cases", "Violin"]
    },
    {
        "firstName": "Kristian",
        "lastName": "Vos",
        "number": "unknown",
        "likes": ["Javascript", "Gaming", "Foxes"]
    }
];

function lookUpProfile(firstName, prop){
// Only change code below this line
  var arr = 0;

  for(var i = 0; i < contacts.length; i++) {
    for(var x = 0; x < contact[i]; x++) {

    }
  }

La consigne de l'exercice :

We have an array of objects representing different people in our contacts lists.

A lookUpProfile function that takes firstName and a property (prop) as arguments has been pre-written for you.

The function should check if firstName is an actual contact's firstName and the given property (prop) is a property of that contact.

If both are true, then return the "value" of that property.

If firstName does not correspond to any contacts then return "No such contact"

If prop does not correspond to any valid properties then return "No such property"

"Kristian", "lastName" should return "Vos"
"Sherlock", "likes" should return ["Intriguing Cases", "Violin"]
"Harry","likes" should return an array
"Bob", "number" should return "No such contact"
"Akira", "address" should return "No such property"

Voila merçi ! :)