example1.js

console.log( response( new Date().getHours() ) );

example2.js

var time = 0;

setInterval(function() {
  $('#msg').text( response(time) );
  console.log(time, $('#msg').text());
  time = time + 1;
  if (time == 24) {
    time = 0;
  }
}, 1000);

greeting.js

function response(time) {
  return ( time >= 0 && time < 5 ) ? 'こんばんは' : ( ( time >= 5 && time < 11 ) ? 'おはようございます' : ( time >= 11 && time < 16 ) ? 'こんにちは' : 'こんばんは' );
}