// HTML
                                      ↓
<a id="change_text" id=Filip>Filip 1</a>

<a id="change_text">evvi 2</a>



<h3 id="text_change">This should change</h3>

// javascript

document.getElementById("demo").addEventListener("click", change_text( first_name );

function change_text(Uid)
{
  document.getElementById("text_change").innerHTML = "this is "+uid;
}