​x
 
<!DOCTYPE html>
<html>
<body>
​
<form action="/demo/htmldom/action_page.php">
  密码：<input type="password" id="myPsw" name="usr_psw" required>
  <input type="submit">
</form>
​
<p>请单击“试一试”按钮，了解是否必须在提交表单前填写密码字段。</p>
​
<button onclick="myFunction()">试一试</button>
​
<p id="demo"></p>
​
<script>
function myFunction() {
  var x = document.getElementById("myPsw").required;
  document.getElementById("demo").innerHTML = x;
}
</script>
​
</body>
</html>
​