怎么让select为必选项

作者：袖梨 2022-07-02

YPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w***3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

提示：您可以先修改部分代码再运行

<title> new document </title>
  <meta name="generator" content="editplus">
  <meta name="author" content="">
  <meta name="keywords" content="">
  <meta name="description" content="">

<select id="y" name="y">
	<option value="">年</option>
	<option value="1982">1982</option>
	<option value="1983">1983</option>
	<option value="...">...</option>
  </select>
  <select id="m" name="m">
	<option value="">月</option>
	<option value="1">1</option>
	<option value="2">2</option>
	<option value="...">...</option>
  </select>
  <select id="d" name="d">
	<option value="">日</option>
	<option value="1">1</option>
	<option value="2">2</option>
	<option value="...">...</option>
  </select>
  <input type="button" value="提交" onclick="javascript:check();">
   <script type="text/javascript">
   <!--
	function check()
	{
		var y,m,d;
		var o_y = document.getElementById('y');
		var o_m = document.getElementById('m');
		var o_d = document.getElementById('d');
		y = o_y.options[o_y.selectedIndex].value;
		m = o_m.options[o_m.selectedIndex].value;
		d = o_d.options[o_d.selectedIndex].value;
		if(y=='' || m=='' || d=='')
			alert('没选完');
		else
			alert('选完了');

}
   //-->
   </script>

提示：您可以先修改部分代码再运行

怎么让select为必选项

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