findWaldo.js

// The second argument/parameter is expected to be a (callback) function
const findWaldo = function(names, found) {
  names.forEach(e => {
    if (e === 'Waldo') found();
  });
};

const actionWhenFound = function() {
  console.log('Found him!');
};

findWaldo(['Alice', 'Bob', 'Waldo', 'Winston'], actionWhenFound);