官网： https://www.npmjs.com/package/date-util
日期格式：
- d: Day of the month without leading zeros
- dd: Day of the month, 2 digits with leading zeros
- ddd: A textual representation of a day, three letters
- dddd: A full textual representation of the day of the week
- m: Numeric representation of a month, without leading zeros
- mm: Numeric representation of a month, with leading zeros
- mmm: A short textual representation of a month, three letters
- mmmm: A full textual representation of a month, such as January or March
- yy: A two digit representation of a year
- yyyy: A full numeric representation of a year, 4 digits
- h: 12-hour format of an hour without leading zeros
- hh: 12-hour format of an hour with leading zeros
- H: 12-hour format of an hour without leading zeros
- HH: 24-hour format of an hour with leading zeros
- M: Minutes without leading zeros
- MM: Minutes with leading zeros
- s: Seconds, without leading zeros
- ss: Seconds, with leading zeros
- l: Milliseconds, 3 digits
- L: Milliseconds without leading zeros
- t: Lowercase Ante meridiem and Post meridiem, 1 digit
- tt: Lowercase Ante meridiem and Post meridiem, 2 digits
- T: Uppercase Ante meridiem and Post meridiem, 1 digit
- TT: Uppercase Ante meridiem and Post meridiem, 2 digits
- Z: Difference to Greenwich time (GMT) in hours, with "GMT" word
- o: Difference to Greenwich time (GMT) in hours, without "GMT" word
- S: English ordinal suffix for the day of the month, 2 characters
基本用法：
- new Date().format("yyyy/mm/dd");
- new Date().strtotime("+1 day");
- new Date().strtotime("next month +1 day");
- new Date().strtotime("last sunday");
- new Date().strtotime("last sunday").format("yyyy/mm/dd");