var database = [
  {
    username: "Mike",
    password: "pass123"
  },
  {
    username: "John",
    password: "pass555"
  },
  {
    username: "Rome",
    password: "passb99"
  }
];

var newsFeed = [
  {
    username: "Robby",
    timeline: "So tired of all that learning"
  },
  {
    username: "Rick",
    timeline: "Javascript is soooo cool!"
  }
];

var userNamePrompt = prompt("What's your username?");
var passwordPrompt = prompt("What's your password?");

function isUserValid(username, password) {
  for (var i = 0; i < database.length; i++) {
    if(database[i].username === username && database[i].password === password) {
      return true;
    }
  }
  return false;
}

function signIn(username, password) {
  if(isUserValid(username, password)) {
    console.log(newsFeed);
  } else {
    console.log("You are not a user");
  }
}

signIn(userNamePrompt, passwordPrompt);