[javascript] onclick, onfocus등 여러 속성

HTML태그내의 속성 중 on접두사를 갖는 속성은 이벤트 속성. (~ 했을때)
<  input type='button' value='버튼' onclick="자바스크립트 코드">

                                              ===> 주로 함수 호출
                                     ===> 버튼을 클릭했을때
     onfocus : 포커스가 들어왔을때                                              
     onblur : 포커스를 잃었을때
     onchange : select태그에서 선택을 바꾸었을때
     onkeydown : 키보드를 눌렀을때
     onkeyup   : 키보드 땠을때
     onmouseover   : 마우스가 진입했을때, 엘리먼트위에 올려졌을때 
     onmouseout    : 마우스가 나갔을때
     onmousedown   : 마우스를 클릭했을때