Edit in JSFiddle

function test001() {
  alert("클릭하였습니다.");
}

function test002() {
  var str = document.getElementById("str");
  str.innerHTML = "안녕하세요.";
}

function test003() {
  var str = document.getElementById("str");
  str.innerHTML = "";
}

function test() {
  var date = new Date();
  document.getElementById("timer").innerHTML = date;
}
setInterval(test, 1000);

<h1 id="timer"></h1>
<input type="button" value="click" onclick="test001()" />
<br>
<span onmouseover="test002()" onmouseout="test003()">마우스를 올려보세요.</span>
<span id="str"></span>