likes.js

let names = ['billy', 'jill', 'peter', 'john', 'richard'];
function likes(names) {
  return {
    0: 'no one likes this',
    1: `${names[0]} likes this`, 
    2: `${names[0]} and ${names[1]} like this`, 
    3: `${names[0]}, ${names[1]} and ${names[2]} like this`, 
    4: `${names[0]}, ${names[1]} and ${names.length - 2} others like this`, 
  }[Math.min(4, names.length)]
}
likes(names);


////
function likes (names) {
  var templates = [
    'no one likes this',
    '{name} likes this',
    '{name} and {name} like this',
    '{name}, {name} and {name} like this',
    '{name}, {name} and {n} others like this'
  ];
  var idx = Math.min(names.length, 4);
  
  return templates[idx].replace(/{name}|{n}/g, function (val) {
    return val === '{name}' ? names.shift() : names.length;
  });
}


////
function likes(names) {
  names = names || [];
  switch(names.length){
    case 0: return 'no one likes this'; break;
    case 1: return names[0] + ' likes this'; break;
    case 2: return names[0] + ' and ' + names[1] + ' like this'; break;
    case 3: return names[0] + ', ' + names[1] + ' and ' + names[2] + ' like this'; break;
    default: return names[0] + ', ' + names[1] + ' and ' + (names.length - 2) + ' others like this';
  }
}


////
function likes(names) {
  names.length === 0 && (names = ["no one"]);
  let [a, b, c, ...others] = names;
  switch (names.length) {
    case 1: return `${a} likes this`;
    case 2: return `${a} and ${b} like this`;
    case 3: return `${a}, ${b} and ${c} like this`;
    default: return `${a}, ${b} and ${others.length + 1} others like this`;
  }
}


////
function likes (names) {
  var format = {
    0: "no one likes this",
    1: "{0} likes this",
    2: "{0} and {1} like this",
    3: "{0}, {1} and {2} like this"
  }[names.length] || "{0}, {1} and {n} others like this";
  
  return format.replace(/{([\dn])}/g, function (_, n) {
    return n == 'n' ? names.splice(2).length : names[parseInt(n, 10)];
  });
}


////
function likes (names) {
  var templates = [
    'no one likes this',
    '{name} likes this',
    '{name} and {name} like this',
    '{name}, {name} and {name} like this',
    '{name}, {name} and {n} others like this'
  ];
  var idx = Math.min(names.length, 4);
  
  return templates[idx].replace(/{name}|{n}/g, function (val) {
    return val === '{name}' ? names.shift() : names.length;
  });
}


////
function likes(names) {
  if(names.length === 0) return "no one likes this";
  if(names.length === 1) return names[0] + " likes this";
  if(names.length === 2) return names[0] + " and " + names[1] + " like this";
  if(names.length === 3) return names[0] + ", " + names[1] + " and " + names[2] + " like this";
  return names[0] + ", " + names[1] + " and " + (names.length - 2) + " others like this";
}