JS中function eventInfo参数，求详细讲解，有例子更好

Question

  function buttonClickHandler(eventInfo) {
        var userName = document.getElementById("nameInput").value;
        var greetingString = "Hello, " + userName + "!";
        document.getElementById("greetingOutput").innerText = greetingString; 
    }
这边eventInfo真心想不通啊，
激活
              var helloButton = document.getElementById("helloButton");
            helloButton.addEventListener("click", buttonClickHandler, false);
小弟菜菜求指点

Answer 1

helloButton.addEventListener("click", function(){buttonClickHandler(something)}, false); 试试