array_names.js

var names = [
  ["John", "Brown"],
  ["Lisa", "May"],
  ["Henry", "Ford"],
];

function displayLastName(inputName) {
  // first we are going to map through the names array
  // return null for anything that doesn't match
  return names
    .map(function(name, index) {
      console.log('first map: ', index, name);
      if (name[0] === inputName) return name[1];
      return null;
    })
    // now we filter all the nulls out to keep the returned array clean
    .filter(function(element) {
      console.log('filter: ', element);
      return element !== null;
    })[0];
    // since filter returns an array we just grab the first result
    // if there is more than one match, we will still just grab the first result
    // this is something to consider as part of your application design
}

var result = displayLastName('John');

console.log(result);