

<input type="text" required>
input태그 속성에 required 넣어주기
Browser : <select name="인터넷브라우저">
<option value="크롬">크롬</option>
<option value="dog">사파리</option>
<option value="cat">엣지</option>
</select><br>
select와 option 태그 사용
Gender : <input type="radio" name="gender">Male<input type="radio" name="gender">Female<br>
하나만 선택되게 하고 싶은 input 태그 속성에 name을 같게 하면 하나만 선택하게 바꿀 수 있다!
Favorite : <input type="checkbox">HTML<input type="checkbox">JAVA<input type="checkbox">JavaScript<br>
동그라미는 radio, 네모는 checkbox 속성이다!

function btn() {
if (document.getElementById("first").value === ""
|| document.getElementById("last").value === ""
|| document.getElementById("email").value === "") {
return false
} else { alert('제출 완료!') }
}
버튼을 누를 때 값이 없으면 처리되지 않도록 함
<script>
function btn() {
if (document.getElementById("first").value === ""
|| document.getElementById("last").value === ""
|| document.getElementById("email").value === "") {
return false
} else { alert('제출 완료!') }
}
</script>
<form>
First name : <br>
<input type="text" id = "first" required><br>
Last name : <br>
<input type="text" id = "last" required><br>
Email : <br>
<input type="text" id = "email" required><br>
Gender : <input type="radio" name="gender" id="check" required checked>Male<input type="radio" name="gender" id="check" required>Female<br>
Favorite : <input type="checkbox">HTML<input type="checkbox">JAVA<input type="checkbox">JavaScript<br>
Browser : <select name="인터넷브라우저">
<option value="크롬">크롬</option>
<option value="dog">사파리</option>
<option value="cat">엣지</option>
</select><br>
Birthday : <input type="date"><br>
<input type="submit" value="제출" onclick="btn()">
</form>