window.onload = function() {
document.getElementById("user_id").value = "아이디"
document.getElementById("user_pwd").value = "비밀번호"
}
var inputField = "";

function msg(var1, var2, var3) {
if(var1 == "") {
document.getElementById(var2).value = var3;
} else {
document.getElementById(var2).value = var1;
}
}

function delAlt(obj, elm, chk) {
document.getElementById(elm).value = inputField;
document.getElementById(elm).onblur = function () {msg(this.value, elm, chk)};
}