<script type="text/javascript">   function show(){    var firstDay = new Date();    var year = firstDay.getFullYear();    var month = firstDay.getMonth() + 1;    firstDay.setDate(1); //当月第一天    var lastDay = new Date(year, month, 0); //次月第一天的前一天    alert(     year + "-" + month + "-" + firstDay.getDate() + "\n" +      year + "-" + month + "-" + lastDay.getDate()    );   }  </script>  <input type="button" onclick="show()" value="Show"/>