Day. JS common methods

Preface

• Day.js Instead of modifying local Date.prototype,Day.js Yes Date Objects are encapsulated , Just call Dayjs() that will do .
• relative moment.js nothing more ,day.js It's smaller , Only 2KB about ;moment.min.js Yes 16.7KB.
• For ordinary projects , There are only a few operations corresponding to time （ format 、 Inquire about 、 Calculation ）, These are based on Day.js It's enough . also Day.js The documentation is relatively simple 、 Clear ！

This article compares with the previous moment.js The article
Day.js Official documents
 

Many examples of the current article are processed at the current time , The current time is ：2022-04-20
 

1. Initialization date / Time

dayjs().format('YYYY-MM-DD');		    //  Initialization date 
dayjs().format('YYYY-MM-DD HH:mm:ss');  //  Initialization date time 

2. Format date / Time

dayjs(value).format('YYYY-MM-DD');			//  Initialization date 
dayjs(value).format('YYYY-MM-DD HH:mm:ss'); //  Initialization date time 

3. Add / reduce

dayjs().add / dayjs().subtract Represents addition and subtraction in the current time ;
dayjs(value).add / dayjs(value).subtract Represents at a specified time （value） Go up and add and subtract ;

dayjs().add(7, 'day').format('YYYY-MM-DD');   // 2022-04-27  today （2022-04-20） add 7 God 
dayjs().add(1, 'month').format('YYYY-MM-DD');   // 2022-05-20  today （2022-04-20） Plus January 

dayjs().subtract(2, 'year').format('YYYY-MM-DD');   // 2020-05-20  today （2022-04-20） subtract 2 year 
dayjs().subtract(2, 'hour').format('YYYY-MM-DD HH:mm:ss');   // 2022-04-20 14:03:39  Today, now （2022-04-20 16:03:39） subtract 2 Hours 

List of all available units ：

Company	abbreviation	describe
week	w	Zhou
day	d	week ( Sunday 0, Saturday 6)
month	M	month (0-11)
year	y	year
hour	h	Hours
minute	m	minute
second	s	second
millisecond	ms	millisecond

4. Get the first or last day of a year or month

Get the first day of a month and a year ：

dayjs().startOf('year').format('YYYY-MM-DD HH:mm:ss')   // 2022-01-01 00:00:00 =>  The hours, minutes and seconds formatted on the first day are 0
dayjs().startOf('month').format('YYYY-MM-DD')   // 2022-04-01

Get the last day of a month and a year ：

dayjs().endOf('year').format('YYYY-MM-DD HH:mm:ss')   // 2022-12-31 23:59:59 =>  Last time   The formatted hours, minutes and seconds are 23:59:59
dayjs().endOf('month').format('YYYY-MM-DD')   // 2022-04-30

5. Get the day of the week

dayjs().day() : return 0( Sunday ) To 6( Saturday ) The number of

You can only accept 0-6 The number of ：
dayjs().day(6).format('YYYY-MM-DD')： Get the date of the last Saturday => 2022-04-23
dayjs().day(0).format('YYYY-MM-DD')： Get the date of the last Sunday => 2022-04-17

6. Get milliseconds

dayjs('2019-01-25').valueOf() or dayjs().valueOf()

7. Get time difference （ The default output is in milliseconds ）

dayjs('2019-01-25').diff('2018-06-05', 'month');         // 7
dayjs('2019-01-25').diff(dayjs('2018-06-05'), 'month');  // 7

List of all available output units ：

Company	abbreviation	describe
week	w	Zhou
day	d	week ( Sunday 0, Saturday 6)
month	M	month (0-11)
year	y	year
hour	h	Hours
minute	m	minute
second	s	second
millisecond	ms	millisecond （ Default output unit ）

8. When getting 、 branch 、 second

current time ：2022-04-20 16:55:55 ;
Most of the following methods will overflow forward ; If milliseconds exceed 999, Will last until seconds ; Seconds more than 59, Will last until , The situation here is particularly prominent when setting ！

    console.log('----- Year of acquisition ', dayjs().year());    // ==>> 2022
    console.log('----- Get the month ', dayjs().month());   // 0 To 11 The number of  ==>> 3
    console.log('----- Get week ', dayjs().day());   // 0( Sunday ) To 6( Saturday ) The number of  ==>> 3
    console.log('----- Get days ', dayjs().date());    // 1 To 31 The number of  ==>> 20
    console.log('----- For hours ', dayjs().hour());  // 0 To 23 The number of  ==>> 16
    console.log('----- Get minutes ', dayjs().minute());// 0 To 59 The number of  ==>> 55
    console.log('----- Get seconds ', dayjs().second());  // 0 To 59 The number of  ==>> 55
    console.log('----- Get milliseconds ', dayjs().millisecond());  // 0 To 999 The number of  ==>> 333

9. Turn milliseconds into minutes and seconds

//  The following milliseconds represent ：2022-04-20 17:43:20
const timestr = 1650447800731;   //  The millisecond value must be number type , If it is string, The result may be different from what you think 
console.log(' Turn milliseconds into years - month - Japan   when : branch : second ', dayjs(timestr).format('YYYY-MM-DD HH:mm:ss'));
console.log(' Year of acquisition ', dayjs(timestr).year()); // 
console.log(' Get the month ', dayjs(timestr).month());
console.log(' Get days ', dayjs(timestr).date());
console.log(' When getting ', dayjs(timestr).hour());
console.log(' Get points ', dayjs(timestr).minute());

Be careful ： here year()、month()、date()、hour()、minute()、second()、millisecond() And other methods can be used

10. Judge whether one date is after another isAfter

// day.js  by  2022-04-20
console.log('isAfter', dayjs().isAfter(dayjs('2011-01-01'))) 			 	// true
console.log('isAfter', dayjs('2022-04-20').isAfter(dayjs('2022-04-21')))	// false
console.log('isAfter', dayjs('2022-04-20').isAfter(dayjs('2022-04-20')))	//  Same as false

11. Judge whether one date is before another isBefore

// day.js  by  2022-04-20
console.log('isBefore', dayjs().isBefore(dayjs('2011-01-01')))             // false
console.log('isBefore', dayjs('2022-04-20').isBefore(dayjs('2022-04-21'))) // true
console.log('isBefore', dayjs('2022-04-20').isBefore(dayjs('2022-04-20'))) //  The date is also the same when false

12. Judge whether the two dates are the same isSame

// day.js  by  2022-04-20
console.log('isSame', dayjs().isSame(dayjs('2011-01-01')))  			// false
console.log('isSame', dayjs('2022-04-20').isSame(dayjs('2022-04-21')))	// false
console.log('isSame', dayjs('2022-04-20').isSame(dayjs('2022-04-20')))	// true

13. Judge whether a date is between two dates IsBetween

Be careful :
This feature depends on IsBetween plug-in unit
How to use... Will also be demonstrated here Day.js Plug in for

import dayjs from 'dayjs'	//  introduce dayjs
import isBetween from 'dayjs/plugin/isBetween'	//  Introduce related plug-ins 

created() {
    
   dayjs.extend(isBetween); //  Mount plug-ins 
   //  The use of plug-in 
   console.log('isBetween', dayjs('2010-10-20').isBetween('2010-10-19', dayjs('2010-10-25')) )
}

 

Day.js There are Same or before IsSameOrBefore and Same or later IsSameOrAfter Methods , It can be used according to the actual demand , But these two methods need to rely on the corresponding plug-ins ！

Be careful ：
isAfter、isBefore、isSame、IsBetween The default is to change the date to milliseconds To compare , So these two methods have a second parameter . That is, specify the granularity of the comparison
console.log('isBefore', dayjs('2022-04-20').isBefore('2015-01-01', 'year'))

List of all available units ：

Company	abbreviation	describe
date	D	God 00:00
day	d	week 00:00
month	M	The first day of the month 00:00
year	y	1 month 1 Japan 00 spot
week	w	First day of the week 00:00
isoWeek		Zhou (ISO)
hour	h	Hours 00:00:00
minute	m	minute 00:00
second	s	second 00
millisecond	ms	millisecond （ Default comparison unit ）0

 

For more detailed usage, see Official documents
This article is only a record of my learning process , For reference only , If there is a problem , Welcome to point out ！