使用JavaScript切换元素的可见性

尝试使用JavaScript切换元素的可见性.它有效,但我必须先点击一次,这当然不是最佳的.有人能指出我为什么这不能正常工作？

function toggle_visibility(id) {
  var e = document.getElementById(id);
  if(e.style.display == 'block')
    e.style.display = 'none';
  else
    e.style.display = 'block';
}

#foo {
  display: block;
}

Click here to toggle visibility of element #foo
This is foo

function toggle_visibility(id) {
  var e = document.getElementById(id);
  if(e.style.display == 'none')
    e.style.display = 'block';
  else
    e.style.display = 'none';
}

#foo {
  display: block;
}

Click here to toggle visibility of element #foo
This is foo