Detailed explanation of Date type and Math type in Javascript_Basic knowledge

Date type

The Date type in ECMASCript is built on the java.util.Date class in early Java. For this purpose, the Date type uses the number of milliseconds that have elapsed since midnight (0:00) on January 1, 1970 UTC (Coordinated International Time) to save the date.

Create date object

1. Create the current date. No parameters need to be passed in
2. Create a specified date. Parameters need to be passed in, and the number of milliseconds representing the date must be passed in (that is, the number of milliseconds that elapsed from midnight on January 1, 1970 to this date). In order to simplify this calculation process, ECMAScript provides two methods: Date.parse() and Date.UTC().

var now = new Date()//新创建的对象自动获得当前日期和时间
var someDate = new Date('May 25, 2004')
var allFives = new Date(2015, 4, 4, 17, 55, 55)

Date.parse() and Date.UTC()

Date.parse()

Receives a string parameter representing a date, and then attempts to return the milliseconds of the corresponding date based on this string
var someDate = new Date(Date.parse('May 25,2015'))
Note: ECMA-262 does not define which date formats Date.parse() should support, so this method is implementation-specific and often region-specific. In fact, passing the string representing the date to the Date constructor will also call Date.parse() in the background.

Date.UTC()

The parameters are: year, 0-based month, day, hour, minute, second, and millisecond. Only the first two parameters are required. If other parameters are omitted, they are all assumed to be 0.

// GMT时间2016年1月1日午夜0时
var M = new Date(Date.UTC(2016, 0));

// GMT时间2015年5月5日下午5:55:55
var allFives = new Date(Date.UTC(2015, 4, 4, 17, 55, 55));

Note: The Date constructor also mimics Date.UTC(), but with one obvious difference: dates and times are created based on the local time zone rather than GMT. However, the Date constructor still receives the same parameters as Date.UTCf().

Date.now()

Returns the date and time in milliseconds when this method was called.

// 取得开始时间
var start = Date.now();

// 调用函数
doSomthing();

// 取得停止时间
var stop = Date.now();

result = stop - start;

Compatibility: IE9+, Firfox3+, Safari3+, Opera10.5, Chrome. In browsers that do not support it, the same purpose can be achieved by using the + operator to convert the Date object into a string

Date formatting method

Method to format date into string

1. toDateString()
2. toTimeString()
3. toLocalDateString()
4. toLocalTimeString()
5. toUTCString()
   

Recommended: toUTCString()

Note: UTC date refers to the date value without time zone deviation (converting the date to GMT time).

Math type

min( ) and max( )

var value = [1,2,3,4,5,6,7,8];
var max = Math.max.apply(Math, values);

Rounding method

Math.ceil( ):向上舍入
Math.floor( ):向下舍入
Math.round( ):四舍五入
random( )
Math.random( )方法返回介于0和1之间的一个随机数，不包括0和1
var num = Math.floor(Math.random()*10, + 1)//返回1-10之间的数