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 {
		alert("Sorry, incorrect credentials");
	}
}

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

signIn(userNamePrompt, passwordPrompt);