Detailed explanation of JS built-in objects Math and Date

1. Methods of Math object

1. Find the maximum value method
①min()
Syntax: Math.min (num1,num2…numN)
Function: Find the minimum value in a set of numbers.
Return value: Number.

②max()
Syntax: Math.max(num1,num2…numN)
Function: Find the maximum value in a set of numbers.
Return value: Number.

<script>
    var min=Math.min(5,-4,0,9,108,-55);
    console.log(min);//-55
    
    var min1=Math.min(5,-4,0,9,108,-55,"abc");
    console.log(min1);//NaN
    
    var max=Math.max(88,0,6,85,199);
    console.log(ma);//199
</script>

2. Rounding method

①ceil()
Syntax: Math.ceil(num)
Function: Round up, that is, return greater than The smallest integer of num.
Return value: Number.

②floor
Syntax: Math.floor(num)
Function: Round down and return the integer part of num.
Return value: Number.

③round()
Syntax: Math.round (num)
Function: Round the value to the nearest integer.
Return value: Number.

var num=Math.ceil(189.99);
console.log(num);//190
var num1=Math.ceil(189.09);
console.log(num1);//190


var num2=189.09;
var int1=Math.ceil(num2);//190
var int2=Math.floor(num2);//189

var int3=Math.round(num2);//189
var num3=189.69;
var int3=Math.round(num3);//190

3. Find the absolute value
①abs()
Syntax: Math.abs (num)
Function: Return the absolute value of num.
Return value: Number.

var nums=-55;
console.log(Math.abs(nums));//55

4. Generate random numbers
①random()
Syntax: Math.random()
Function: Return a random number greater than or equal to 0 and less than 1.
Return value: Number.

Instructions:
The formula for finding a random integer between n and m:
random=Math.floor(Math.random()*(m-n 1) n);

var random=Math.random();
console.log(random);//每一次刷新都不一样，小于1的随机数：0.458541256325412

//生成x~x之间的随机整数
function getRandom(n,m){
    var choise=m-n+1;//随机整数的个数
    return Math.floor(Math.random()*choise+n);
}
var random1=getRandom(2,6);
console.log(random1);//5 3 2...

2. Date object

1. Method of creating date object
Syntax: new Date();
Function: Create a date and time Object
Return value: Returns the current date and time object without passing parameters.

Note:
If you want to create a date object based on a specific date and time, you must pass in the number of milliseconds representing the date or a set of comma-separated values ​​representing the year, month, day, hour, minute, and second. parameters.

2. Method of obtaining date and time
1. getFullYear(): Returns the 4-digit year
2. getMonth(): Returns the Month, the return value is 0-11
3. getDate(): returns the number of days in the month
4. getDay(): returns the week, the return value is 0-6
5. getHours(): returns Hour
6, getMinutes(): Returns minutes
7, getSeconds(): Returns seconds
8, getTime(): Returns the number of milliseconds representing the date

<script>
    //创建一个日期时间对象
    var weeks=["日","一","二","三","四","五","六"],
        today=new Date();
    console.log(today);//Thu Jan 04 2018 15:43:49 GMT+0800 (中国标准时间)
    
    var today=new Date(),
        year=today.getFullYear(),
        month=today.getMonth()+1,
        date=today.getDate(),
        week=today.getDay(),
        hours=today.getHours(),
        minutes=today.getMinutes(),
        seconds=today.getSeconds(),
        times=today.getTime(),
        time=year+'年'+month+'月'+date+'日'+hours+'时'
            +minutes+'分'+seconds+'秒 星期'+weeks[week];
            
    console.log("现在是："+time); //现在是：2018年1月4日15时51分41秒 星期四
    console.log(times);//从1970年1月1日00:00:00开始到现在时间的毫秒数：1515052409017
</script>

3. Methods for setting date and time
1. setFullYear(year): Set the 4-digit year
2. setMonth(mon): Set the month in the date, starting from 0, 0 means January
3. setDate(): Set the date
4. setDay(): Set the day of the week, starting from 0, 0 means Sunday
5. setHours(): Set the hours
6. setMinutes(): Set the minutes
7. setSeconds(): Set seconds
8. setTime(): Set the date in milliseconds, which will change the entire date

//创建一个日期时间对象
var today=new Date();
today.setFullYear(2015);
console.log(today.getFullYear());//2015

today.setMonth(8);
console.log(today.getMonth());//8

today.setMonth(13);
console.log(today.getMonth());//1

Case: the day of the week after 50 days

<script>
    var today=new Date();
    
    //第一种做法
    //today.setDate(today.getDate()+50);
    //console.log(today.getDay());
    //5
    
    //第二种做法
    var weeks=["日","一","二","三","四","五","六"];
    var year=today.getFullYear();
    var month=today.getMonth();
    var day=today.getDate();
    //创建一个目标日期对象
    var temp = new Date(year,month,day+50);
    console.log("50天后的今天是："+temp.getFullYear()+'-'+(temp.getMonth()+1)+'-'+temp.getDate()
                                +'-'+'星期'+weeks[temp.getDay()]);
    //50天后的今天是：2018-2-23-星期五
</script>

Recommended tutorial: "JS Tutorial"

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