jquery macro and confluence

Some things...

You don't seem to be using jQuery at all, so why both with the {jquery} macro. Also, this is being displayed in the page, so don't add the head or body tags.

Try this:

{html}
<script>
  function displayMessage(){
      alert('Hello World!');
  }
</script>
<form><input id="clickMeInput" type="button" value="Click me!" onclick="displayMessage()" /></form>

<p>By pressing the button above, a function will be called. The function will alert a message.</p>
{html}

If you want to use jQuery, Atlassian already bundle it in Confluence, but their version is referenced using AJS.$ rather than just $.

Try this:

{html}
<script>

  AJS.toInit(function(){ // use instead of $(document).ready()
    AJS.$('#clickMeInput').click(function(){
      alert('Hello World!');
    })
  })

</script>

<form><input id="clickMeInput" type="button" value="Click me!" /></form>
 
<p>By pressing the button above, a function will be called. The function will alert a message.</p>
{html}