On the basic knowledge of date and time in javascript
- 2021-07-02 23:15:34
- OfStack
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Before you introduce Date objects, you should first learn something about dates and times. For example, leap year, UTC and so on. A deeper understanding of these helps to better understand Date objects in javascript. This article will introduce the basic knowledge of javascript about date and time
Standard Time 1 Generally speaking, standard time refers to GMT and UTC, which used to be GMT and now is UTC
GMT
Greenwich Mean Time (GMT) is the standard time at the Royal Greenwich Observatory on the outskirts of London, because the prime meridian is defined as the meridian passing through it
In theory, noon GMT refers to the time when the sun crosses the Greenwich meridian (that is, when it is at its highest point over Greenwich). Due to the uneven velocity of the Earth in its elliptical orbit, this time may be 16 minutes away from the actual solar time
The Earth's daily rotation is somewhat irregular and is slowing down slowly. Therefore, Greenwich Mean Time is no longer used as standard time. The current standard time-Universal Coordinated Time (UTC) is provided
UTC
Universal Coordinated Time (UTC), also known as Universal Time, Universal Standard Time and Universal Coordinated Time, is a time measurement system based on atomic time and seconds, which is as close as possible to Universal Time in time
This time system has been used in many Internet and World Wide Web standards. The time difference between mainland China, Hong Kong, Macau, Taiwan, Mongolia, Singapore, Malaysia, Philippines and Western Australia and UTC is +8, that is, UTC +8
In the military, the Coordinated Universal Time Zone is represented by "Z". Since Z uses "Zulu" for radio communication, UTC will also be called "Zulu time"
Date time string format
ECMAScript defines a date-time string interchange format based on the simplified ISO 8601 extended format
The full date and time format is: YYYY-MM-DDTHH: mm: ss. sssZ
[Note] The prefix 0 cannot be omitted, otherwise an error will be reported in the case of complete format
YYYY Gregorian middle-aged 10 Binary number, if the parameter value is in 0-99 Is added to it 1900
- Directly in the string with " - " ( Dash ) Appear twice
MM 1 The month of the year, from 01(1 Month ) To 12(102 Month )
DD The date in the month, from the 01 To 31
T Directly in the string with " T "Occurs to indicate the beginning of a time element
HH With two 10 Represented by binary numbers since midnight 0 Hours since
: Directly in the string with " : " ( Colon ) Appear twice
mm Is to use two 10 The number of minutes since the beginning of the hour, expressed by a binary number
ss Is to use two 10 The number of seconds since the beginning of the minute, expressed by a binary number
. Directly in the string with " . " ( Point ) Appear
sss Is to use 3 A 10 The number of milliseconds since the beginning of the second, expressed by a binary number
Z Is the time zone offset, which is determined by (" Z " ( Refer to UTC) Or " + "Or" - ") and the following time expression hh:mm Composition Date only format: YYYY YYYY-MM YYYY-MM-DD
[Note] All numbers must be decimal. If the MM or DD fields are missing, use "01" as their values. If mm or ss fields are missing, use "00" as their value, and for missing sss, use "000" as its value. Use "Z" for missing time zone offsets
Leap year
Years are divided into leap years and peace years, with 365 days in ordinary years and 366 days in leap years. February in leap years is one day longer than ordinary years
A leap year is defined as a year (divisible by 4) and (not divisible by 100) or (divisible by 400)
The formula is: 1 leap in 4 years, not leap in 100 years, and leap again in 400 years
function IsLeapYear(year){
if(typeof year == 'number'){
if((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0){
return 'leap year'
}else{
return 'common year'
}
}
return 'please input number'
}
console.log(IsLeapYear(4));//'leap year'
console.log(IsLeapYear(400));//'leap year'
console.log(IsLeapYear(2000));//'leap year'
console.log(IsLeapYear(1900));//'common year'Month day
There are 12 months in a year, including 30 days in April, June, September and November; If it is a leap year, there are 29 days in February, otherwise, there are 28 days in February. There are 31 days in each month in January, March, May, July, August, October and December
In javascript, the calculation of month starts from 0, so January-December are represented by 0-11 respectively; The calculation of the day starts with 1, and 1 represents the first day, and so on
if(month == 2){
// If it's a leap year
if((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0){
days = 29;
// If it is a normal year
}else{
days = 28;
}
// If it is the first 4 , 6 , 9 , 11 Month
}else if(month == 4 || month == 6 ||month == 9 ||month == 11){
days = 30;
}else{
days = 31;
}In javascript, the abbreviation of month is often used in the date string
1 Month Jan January
2 Month Feb February
3 Month Mar March
4 Month Apr April
5 Month May May
6 Month Jun June
7 Month Jul July
8 Month Aug August
9 Month Sep September
10 Month Oct October
101 Month Nov November
102 Month Dec DecemberWeek
The week begins on Sunday and ends on Saturday, which is represented by 0-6 respectively
In javascript, the shorthand for each week is often used in the date string
Sunday sunday Sun
Week 1 monday Mon
Week 2 Tuesday Tue
Week 3 Wednesday Wed
Week 4 Thursday Thu
Week 5 Fridday Fri
Week 6 Saturday SarTime and second
1 Days = 24 Hours = 24*60(1440) Points = 24*60*60(86400) Seconds = 86,400,000 Milliseconds
1 Points = 60 Seconds
1 Hours = 3600 Seconds
1 Days = 86400 Seconds The Date object returns a number of milliseconds, which often needs to be converted to hours and seconds
date = 100000s
day( Days ) = Math.floor(100000/86400) = 1
hour( Hours ) = Math.floor((100000%86400)/3600) = 3
minute( Points ) = Math.floor((100000%3600)/60) = 46
second( Seconds ) = Math.floor(100000%60)=40
console.log(100000 === 1*86400+ 3*3600+ 46*60+40);//true