常用的一些日期的获取及判断

自定义的Date对象的原型方法，通过为Date对象添加一个名为format的方法，可以将日期格式化为指定的字符串格式

function handleInitDate () {Date.prototype.format = function (format) {var o = {"M+": this.getMonth() + 1, //month"d+": this.getDate(),    //day"h+": this.getHours(),   //hour"m+": this.getMinutes(), //minute"s+": this.getSeconds(), //second"q+": Math.floor((this.getMonth() + 3) / 3),  //quarter"S": this.getMilliseconds() //millisecond}if (/(y+)/.test(format)) format = format.replace(RegExp.$1,(this.getFullYear() + "").substr(4 - RegExp.$1.length));for (var k in o) if (new RegExp("(" + k + ")").test(format))format = format.replace(RegExp.$1,RegExp.$1.length == 1 ? o[k] :("00" + o[k]).substr(("" + o[k]).length));return format;}
}

使用示例
- 全局引入调用后

var currentDate = new Date();
console.log(currentDate.format("yyyy-MM-dd hh:mm:ss")); // 格式化为年-月-日 时:分:秒的形式

判断是否为当月的第一天

function handleJudgeIsFirstDay() {// 获取当前日期var currentDate = new Date();// 获取当月的第一天var firstDayOfMonth = new Date(currentDate.getFullYear(),currentDate.getMonth(),1);// 判断是否是当月的第一天var isFirstDayOfMonth =currentDate.getDate() === firstDayOfMonth.getDate();return isFirstDayOfMonth
}

判断是否为当月的最后一天

function isLastDayOfMonth() {const today = new Date();const nextMonth = new Date(today.getFullYear(), today.getMonth() + 1, 1);return today.getDate() === nextMonth.getDate() - 1;
}console.log(isLastDayOfMonth());

获取某个月的第一天和最后一天

function getFirstAndLastDay(year, month) {var firstDay = new Date(year, month, 1);var lastDay = new Date(year, month + 1, 0);return {firstDay: firstDay,lastDay: lastDay};
}// 调用函数获取2023年12月的第一天和最后一天
var result = getFirstAndLastDay(2023, 11); // 11表示12月
console.log("第一天: " + result.firstDay.getDate());
console.log("最后一天: " + result.lastDay.getDate());

获取本月，上月，下月的第一天和最后一天

function getFirstAndLastDay(year, month) {var firstDay = new Date(year, month, 1);var lastDay = new Date(year, month + 1, 0);return {firstDay: firstDay,lastDay: lastDay};
}function getLastAndNextMonthFirstAndLastDay() {var today = new Date();var thisYear = today.getFullYear();var thisMonth = today.getMonth();// 获取上个月的年份和月份var lastMonthYear = (thisMonth === 0) ? thisYear - 1 : thisYear;var lastMonth = (thisMonth === 0) ? 11 : thisMonth - 1;// 获取下个月的年份和月份var nextMonthYear = (thisMonth === 11) ? thisYear + 1 : thisYear;var nextMonth = (thisMonth + 1) % 12;var lastMonthResult = getFirstAndLastDay(lastMonthYear, lastMonth);var thisMonthResult = getFirstAndLastDay(thisYear, thisMonth);var nextMonthResult = getFirstAndLastDay(nextMonthYear, nextMonth);return {lastMonth: {firstDay: lastMonthResult.firstDay,lastDay: lastMonthResult.lastDay},thisMonth: {firstDay: thisMonthResult.firstDay,lastDay: thisMonthResult.lastDay},nextMonth: {firstDay: nextMonthResult.firstDay,lastDay: nextMonthResult.lastDay}};
}// 调用函数获取上个月、这个月和下个月的第一天和最后一天
var result = getLastAndNextMonthFirstAndLastDay();
console.log("上个月的第一天: " + result.lastMonth.firstDay.getDate());
console.log("上个月的最后一天: " + result.lastMonth.lastDay.getDate());
console.log("这个月的第一天: " + result.thisMonth.firstDay.getDate());
console.log("这个月的最后一天: " + result.thisMonth.lastDay.getDate());
console.log("下个月的第一天: " + result.nextMonth.firstDay.getDate());
console.log("下个月的最后一天: " + result.nextMonth.lastDay.getDate());

获取某个月有几天

function getDaysInMonth(year, month) {return new Date(year, month + 1, 0).getDate();
}var year = 2023;
var month = 11; // 月份从 0 开始，11 表示十二月var daysInMonth = getDaysInMonth(year, month);
console.log("2023年12月有 " + daysInMonth + " 天");

获取今年有几天

function getDaysInYear(year) {return new Date(year, 12, 0).getDate();
}var year = (new Date()).getFullYear();var daysInYear = getDaysInYear(year);
console.log(year + "年有 " + daysInYear + " 天");