JS built-in objects Math and Data

1.Math

(1) Math.PI represents constant π

  console.log(Math.PI)                              //3.1415926535   

(2) Math.max () maximum

        Math.min () minimum

  console.log(Math.max(1,8,9,6,59,658,569,542))             //658
  console.log(Math.min(658,569,542,586,358,785,459,264))    //264

(4) Math.ceil () ceiling, rounding up  

        Math.floor () rounding down floor

  console.log(Math.ceil(3.1))             //4
  console.log(Math.floor(3.7))            //3

(6) Math.round () rounding

console.log(Math.round(3.1))        //3
  console.log(Math.round(3.7))    //4

(7) Math.random random number [0 to 1)

[0~1) :

console.log(Math.random())       //0.8593806925764069

[0~3) :

console.log(Math.random())       //2.7221629645726204

An integer between [0-3]

 console.log(Math.floor(Math.random()*4))  

(8) Math.abs absolute value   

console.log(Math.abs(-3.1))        //3.1    
console.log(Math.abs(3.7))        //3.7

2.Data date and time

(1) new Date () to create the current time

  var date=new Date()                         
  console.log(date) 

(2) Time Format

 var date=new Date()                         
 console.log(date.toLocaleString())    //2019/9/29 下午8:35:13

 

var date=new Date()                         
  console.log(date.toLocaleDateString())     //2019/9/29

 

  var date=new Date()                         
  console.log(date.toLocaleTimeString())  

(3) for specific dates

 var date=new Date()                         
  console.log(date.getFullYear())     //2019

 

var date=new Date()                         

  console.log(date.getMonth()+1)     //

 

var DATE = new new a Date ()                          
  the console.log (date.getDay ()) // 0 Sunday

 

 var date=new Date()                         
  console.log(date.getHours())    //20   

 

 var date=new Date()                         
  console.log(date.getMinutes())   //48

 

 var date=new Date()                         
  console.log(date.getSeconds())

(4) the timestamp from 1970 to the present time in milliseconds total

 var date=+new Date()                         
  console.log(date) 

(5) Countdown

Time difference: T = parseInt ((end timestamp -start timestamp) / 1000)

Day: day = parseInt (T / 3600/24)

H: hour = parseInt (T / 60/60)% 24

分   ：   minute=parseInt（T/60）%60

Sec: second = time% 60