极客教程moment.js moment().startOf() 方法
moment().startOf() 方法 用于改变 Moment 对象，使其设置为给定时间单位的开始。可用的时间单位包括：年、月、季度、周、天、小时、分钟和秒。
语法：
moment().startOf( String );
参数： 此方法接受一个单一的参数，如上所述，并在下面进行描述：
- String： 它是时间单位，从该时间单位开始设置Moment对象。
返回值： 此方法返回设置了值后的变异Moment对象。
注意： 这在普通的Node.js程序中不起作用，因为它需要全局或项目目录中安装外部的moment.js库。
以下命令可用于安装moment.js：
安装moment模块：
npm install moment
下面的示例将演示Moment.js的moment().startOf()方法。
示例1：
const moment = require('moment');
console.log("Current moment is:", moment().toString());
// This will set the moment to 12:00 am today
console.log(
"startOf current moment's day:",
moment().startOf('day').toString()
)
// This will set the moment to the
// first day and hour of this week
console.log(
"startOf current moment's week:",
moment().startOf('week').toString()
)
// This will set the moment to the
// first day and hour of this month
console.log(
"startOf current moment's month:",
moment().startOf('month').toString()
)
// This will set the moment to the
// beginning of the current quarter
// 1st day and hour of month
console.log(
"startOf current moment's quarter:",
moment().startOf('quarter').toString()
)
// This will set the moment to the
// first day and hour of the year
console.log(
"startOf current moment's year:",
moment().startOf('year').toString()
)
输出：
Current moment is:Mon Jul 18 2022 02:33:56 GMT+0530
startOf current moment's day:Mon Jul 18 2022 00:00:00 GMT+0530
startOf current moment's week:Sun Jul 17 2022 00:00:00 GMT+0530
startOf current moment's month:Fri Jul 01 2022 00:00:00 GMT+0530
startOf current moment's quarter:Fri Jul 01 2022 00:00:00 GMT+0530
startOf current moment's year:Sat Jan 01 2022 00:00:00 GMT+0530
示例2：
const moment = require('moment');
console.log("Current moment is:",
moment().toString());
// This will set the moment to the
// first millisecond of the second
console.log(
"startOf current moment's second:",
moment().startOf('second').toString()
)
// This will set the moment to the
// first second of the minute
console.log(
"startOf current moment's minute:",
moment().startOf('minute').toString()
)
// This will set the moment to the
// first minute of the hour
console.log(
"startOf current moment's hour:",
moment().startOf('hour').toString()
)
输出：
Current moment is:Mon Jul 18 2022 02:33:56 GMT+0530
startOf current moment's second:Mon Jul 18 2022 02:33:56 GMT+0530
startOf current moment's minute:Mon Jul 18 2022 02:33:00 GMT+0530
startOf current moment's hour:Mon Jul 18 2022 02:00:00 GMT+0530
参考： https://momentjs.com/docs/#/manipulating/start-of/