<p id="akapit1">Akapit 1</p>
<button id="bt1" onclick="zrodlo(this)">Przycisk 1</button>
<button id="bt2">Przycisk 2</button>
<button id="bt3">Przycisk 3</button>
<script>
function zrodlo(obiekt) 
{
  document.getElementById("akapit1").innerHTML = "Zdarzenie wywołał " + obiekt.innerHTML;
}
document.getElementById("bt2").onclick = function() {zrodlo(this)};
document.getElementById("bt3").addEventListener("click", function() {zrodlo(this)});
</script>
Akapit 1
https://developer.mozilla.org/en-US/docs/Web/API/Element/click_event
https://developer.mozilla.org/en-US/docs/Web/Events