Constructor_ Date constructor

Date Constructors

effect

• Date It's a constructor , But it can also be called directly ;

  • Use new Key word call ： Create a Date Instance object , This instance presents a moment in time ;

  • Call directly ： The return value is a string , Present a moment in time ;

grammar

• new Date([value])
  • new Date()
    • No parameters passed , So the newly created Date Object represents the date and time of the instantiation time ;
  • new Date(value)
    • The parameter is timestamp ： From 1970 year 1 month 1 Japan 00:00:00 UTC（the Unix epoch） Milliseconds since ( That is to say 1970 year 1 month 1 The conversion time between the sum of the number of milliseconds of the day and the number of milliseconds of the parameter )
    • 1 second == 1000 millisecond
  • new Date(year,mounth,[date],[hours],[minutes],[seconds],[milliseconds])
    • The parameters are date and time members , Year and month are required parameters , The rest are optional parameters ：
    • mounth Choose as 0-11, in other words 0 Express 1 month
• Be careful ： If the parameter is a string , The resolution is not local time but UTC Time
  • new Date(‘1655953575839’)
  • new Date(‘2022-1-1’)

Methods of constructors

• Get the timestamp of the current date
  • Date.now()
  • Date.parse() -String type

The method of prototype chain

• [1] Gets the year of the specified date 、 month 、 Japan 、 when 、 branch 、 second 、 millisecond ;

  • year ：getFullYear()
  • month ：getMonth()
  • Japan ：getDate()
  • when ：getHours()
  • branch ：getMinutes()
  • second ：getSeconds()

• Get the day of the week that the specified date belongs to

  • getDay()
  • The return value is 0-6,0 Sunday ;

• Get the timestamp of the specified date

  • getTime()-Number type
  • valueOf()-Number type

Common logic

[1] Today, ( Including today ) Not optional after date

// now() Functions are constructors Date Methods ---> You can get the number of seconds of the current time 
//  The number of milliseconds in a day is  24*3600*1000= 86400000 = 8.64*10 Of 7 Power  = 8.64e7
Date.now() - 8.64e7

[2] Today, ( Not including today ) After date is not optional

Date.now() - 8.64e6

[3] Convert time to timestamp

//  Get the timestamp of the current time -Number data type 
Date.now() 

//  Get the timestamp of the specified time -Number data type 
Number(new Date()) 
new Date().getTime()
new Date().valueOf()

//  Get the timestamp of the current time -string data type 
Date.parse()

[3] Convert timestamp to time

const date = new Date(1655968066474)
//  error - Because the acquisition of month is 0-11, Normal month is 1-12, Normally, you should add 1
console.log(`${
      date.getFullYear()}-${
      date.getMonth()}-${
      date.getDate()}`)
console.log(`${
      date.getFullYear()}-${
      date.getMonth()+1}-${
      date.getDate()}`)