Button event lost after first click

I have a parent HTML page. It embeds an iframe containing a child HTML page.

The child HTML stores a block of HTML, including a "close" button, into a JS variable, and pass this variable to parent JS function upon a click of a "Show" button in the child HTML. This "Show" button has an addEventListener() on click. The goal of this button is to display the block of HTML code on top of the parent HTML.

I managed to make this block of HTML display on top of the parent HTML when I click "Show", the close button in this block will "display: none" upon clicking the cross button.

However, any further click of the "Show" button in the child HTML will not work; the button is broken and has no action.

Child HTML:

var plan0 = '<div class="popup">'+
            '<span id="closeMe">×</span>'+
            'other content here'+
            '</div>';
document.getElementById("open0").addEventListener("click", function(event) {
    event.preventDefault();
    parent.showPopup(plan0);
}

Parent HTML:

 <div>
      <iframe id="channelFrame" scrolling="no" style="width: 100%; border: 1px; overflow: hidden" src="child.html"></iframe>
 </div>

 <div id="popup"></div>

 <script>
       function showPopup(info) {
              var popup = document.getElementById("popup");
              popup.innerHTML = info;
              var closeMe = document.getElementById("closeMe");
              if (closeMe) {
                     closeMe.onclick = function() {
                              popup.style.display = "none";
                              popup.innerHTML = "";
                      }
               }
        }
  </script>

There is no error in console, and the "event" is still clearly marked in the "Show" button.

Where is the error?

On the first click on close, you are hiding the popup with

popup.style.display = "none";

but never un-hide it. Any subsequent actions will happen in a hidden tag, so you don't see anything.

Try something like:

   function showPopup(info) {
          var popup = document.getElementById("popup");
          popup.innerHTML = info;
          popup.style.display = "block";          // <------ show it again
          var closeMe = document.getElementById("closeMe");
          if (closeMe) {
                 closeMe.onclick = function() {
                          popup.style.display = "none";
                          popup.innerHTML = "";
                  }
           }
    }