js获取时间

// 今天

var today = new Date();

today.setHours(0);

today.setMinutes(0);

today.setSeconds(0);

today.setMilliseconds(0);

alert(today);

var oneday = 1000 * 60 * 60 * 24;

// 昨天

var yesterday = new Date(today - oneday);

alert(yesterday);

// 上周一

var lastMonday = new Date(today- oneday * (today.getDay() + 6));

alert(lastMonday);

// 上个月1号

var lastMonthFirst = new Date(today - oneday * today.getDate());

lastMonthFirst = new Date(lastMonthFirst - oneday * (lastMonthFirst.getDate() - 1));

alert(lastMonthFirst);