JSFiddle - React, Tailwind, and code Playground

JavaScript

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){

  for (var i = 0; i < contacts.length; i++) {
  console.log(contacts[i]);
   if (contacts[i].firstName == firstName){
      return i; 
   } 
  }   
}

alert(lookUpProfile("Akira", "likes"));