const animals = ['hippo', 'tiger', 'lion', 'seal', 'cheetah', 'monkey', 'salamander', 'elephant'];

const foundAnimal = animals.findIndex(a => {
  return a === 'elephant';
});
console.log(animals[foundAnimal]); // uses function's returned index to display value

const startsWithS = animals.findIndex(letter => {
  return letter[0] === 's';
});
console.log(startsWithS); // function returns index number of first TRUE element
console.log(animals[startsWithS]); // used to display that element's value