var foo = function(){
  var button = document.createElement('button');
  button.innerHTML = 'click me';
  button.onclick = function(){
    alert('here be dragons');return false;
  };
  // where do we want to have the button to appear?
  // you can append it to another element just by doing something like
  // document.getElementById('foobutton').appendChild(button);
  document.body.appendChild(button);
};