通过 js 获取当月的第一天和最后一天

var firstDate = new Date();
firstDate.setDate(1);
 
var endDate = new Date(firstDate);
endDate.setMonth(firstDate.getMonth()+1);
endDate.setDate(0);

alert("第一天 --> " + new Date(firstDate));
alert("最后一天 --> " + new Date(endDate));