let test = document.getElementById("test");
  
// This handler will be executed only once when the cursor
// moves over the unordered list
test.addEventListener("mouseenter", function( event ) {   
  // highlight the mouseenter target
  event.target.style.color = "purple";

  // reset the color after a short delay
  setTimeout(function() {
    event.target.style.color = "";
  }, 500);
}, false);