Detailed introduction to JavaScript date operation methods
日期操作在JavaScript开发中经常会遇到，尤其是对初学者来说，JavaScript的日期操作比较繁琐，但是必须掌握常用的日期操作方法，本文就简单介绍一下JavaScript操作日期类型的常用方法，希望能给你有所帮助。
获取某个月份的天数
相信大家读小学的时候就知道一年十二个月各有多少天了，这里面有个特殊的存在——2月。闰年的2月有29天，非闰年的2月只有28天。估计不少人跟我一样，已经不记得闰年的规则了，这时候，下面的这个方法就派上用场了。
var date = new Date(2013, 2, 0); date.getDate(); // 28 date = new Date(2012, 2, 0); date.getDate(); // 29
创建Date对象时可以传入三个参数，分别是年、月（0~11，0表示一月）、日，如果日的参数为0，那创建出来的对象表示的就是上个月的最后一天，如此就可以知道上个月有多少天了。
同样的，我们也可以通过这个方法判断某年是否闰年：
function isLeapYear(year) {
return new Date(year, 2, 0).getDate() === 29;
}
isLeapYear(2012); // true获取时区
日期类型的 getTimezoneOffset() 方法可以获取格林威治时间和本地时间之间的时间差，以分钟为单位。例如：
var date = new Date(); var timezoneOffset = date.getTimezoneOffset(); // 中国（东八区）为-480 -timezoneOffset / 60; // 8
把获取到的时间差除以60，再取负值就是所在的时区了。
除此以外，还有一个方法。调用日期类型的 toString() 后，可以得到一段固定格式的日期字符串：
new Date().toString(); // Sun Mar 10 2013 16:41:12 GMT+0800 (中国标准时间)
显而易见，GMT后面的+800就是我们要的时区了，只要通过正则表达式匹配一下就可以拿到该值。
/GMT([+-]\d+)/.test( new Date().toString() ); var timezone = RegExp.$1; // +0800
不过此时的 timezone 变量是字符串，如果要转成数字类型，还要进行一些处理。
计算运行时间
如何测量某段程序的执行时间呢？方法很简单，在执行前记录一次时间，执行后用当前时间减去执行前的时间，就得到结果了：
var startTime = new Date(); // some program console.log(new Date() - startTime);
这里无需手动把日期转换为数字，因为进行减法运算的时候自然会强制转换。这样算出来的结果是毫秒级的，精度不是很够，不过对浏览器端的Javascript来说，也没必要纠结于1毫秒以内的消耗了。
删除cookie
准确地说，我们没法直接通过Javascript删除cookie。要想把某个cookie从这个世界抹杀掉，唯一的办法就是让它过期，这样浏览器的内建机制就会把它自动干掉。
而要让cookie过期，最直截了当的方法就是把它的过期时间设为最小值。Javascript里面能表示的最小日期就是1970年1月1日0时0点0分，通过 new Date(0) 就可以创建出这样一个日期对象：
var cookieName = 'name'; // cookie名 document.cookie = cookieName + '=' + '; expires=' + new Date(0).toUTCString();
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