replace [JavaScript snippet]

function main() {
  
  var str = "fourty-two: 42";

  var rep = str.replace('42', 'FOURTY-TWO');
  txt_out(rep);

  rep = str.replace(/o/, 'X');
  txt_out(rep);
  
  rep = str.replace(/o/g, 'X');
  txt_out(rep);

  rep = str.replace(/[aeiou]/g, 'X');
  txt_out(rep);

  rep = str.replace(/(\w)/g, '$1$1');
  txt_out(rep);

  rep = str.replace(/(\d)/g, function(s) {return parseInt(s)+1;});
  txt_out(rep);
}