javascript - 检查是否选中所有单选按钮

Question

我正在尝试为所有输入添加一个公共(public)类gender。然后我比较它们是否未检查，并警报为空。我如何正确检查是否所有按钮都已选中？

$( ".btn" ).click(function( event ) {
event.preventDefault;
if(  !$('input .gender').is(":checked") ) alert(" empty");
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<form>
<input class="gender"  type="radio" name="answer[1]" value="male"> Male<br>
<input class="gender" type="radio" name="answer[1]" value="female"> Female<br>
<input class="gender" type="radio" name="answer[1]" value="other"> Other<br>
<br><br>

<input class="gender"  type="radio" name="answer[2]" value="PHP"> PHP<br>
<input class="gender" type="radio" name="answer[2]" value="Pyhon"> Python<br>
<input class="gender" type="radio" name="answer[2]" value="Java"> Java<br>
<input class="btn" type="submit" value="check">
</form>

Answer 1

我将选择选中的单选按钮，然后验证它们的长度是否等于单选字段的数量:

$( ".btn" ).click(function( event ) {
  event.preventDefault();
  if ($('input[type=radio]:checked').length !== 2) console.log("at least one is empty");
  else console.log('pass')
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<form>
<input class="gender"  type="radio" name="answer[1]" value="male"> Male<br>
<input class="gender" type="radio" name="answer[1]" value="female"> Female<br>
<input class="gender" type="radio" name="answer[1]" value="other"> Other<br>
<br><br>

<input class="gender"  type="radio" name="answer[2]" value="PHP"> PHP<br>
<input class="gender" type="radio" name="answer[2]" value="Pyhon"> Python<br>
<input class="gender" type="radio" name="answer[2]" value="Java"> Java<br>
<input class="btn" type="submit" value="check">
</form>

(preventDefault 是一个需要运行的函数，而不是需要声明的独立属性。)