const names = ['john', 'smith', 'karl'];

const get = (arr, str) => {
  if ( str === undefined) {
    return arr
  }
  for (let i = 0; i < arr.length; i += 1)
  console.log(`${str} ${arr[i]}`)
  
}

get(names, 'Mr')

let names = ['john', 'smith', 'karl'], str = 'Mr ';

names = names.map((e) => str+e);

console.log(names)

const names = ['john', 'smith', 'karl'];

const get = (arr, str) => arr.map(v=>str?`${str} ${v}`:v)
console.log(get(names, 'Mr'))
console.log(get(names))