Built in object (bottom)

Date object

Date Object is used to process date and time

Constructor to define a date object :

var Date object =new Date( Parameters )

Parameter format ：MM( month )  DD( Japan ),YYYY( year ),hh:mm:ss

Example ：

var  today=new Date();   // Returns the current date and time

var tdate=new Date("9 1,2022,14:38:12");// Return to a specific time

The first way of writing :

Recommended The second way of writing :

The point of attention is to ensure that ten seconds to : Division , Year, month and day are divided by blank numbers , Point segmentation and other segmentation can .

The third way of writing :

This way is based on   Pass parameters by numeric type , Have a fixed way of writing , And the order shall not be disordered

Common methods

Method say bright

getDate() return Date Every day of the month of the object , Its value is between 1～31 Between

getDay() return Date Every day of the subject's week , Its value is between 0～6 Between （ notes ：0- Sunday ）

getMonth() return Date Month of object , Its value is between 0～11 Between （ notes ：0-1 month ）

getFullYear() return Date Year of object , Its value is 4 digit

If you don't set the hour, minute and second, it will be in 00:00:00 As the default value

getHours() return Date Hours of objects , Its value is between 0～23 Between

getMinutes() return Date Minutes of objects , Its value is between 0～59 Between

getSeconds() return Date The number of seconds of the object , Its value is between 0～59 Between

getSetDate) Change the current date object by setting the date

The first way of writing can only be changed 30 Within days

The first er This writing method can be changed at any time

Function encapsulation and the use of ternary expressions

If you want to print the date , Each has to be IF Judge +0, Then we can use   Function to encapsulate , Use the feature that functions can be called repeatedly to give every month / God / when / Minute and second +0, It can also be in if Use ternary expressions in , More streamlined processing , Eliminate unnecessary lengthy code .

As shown in the figure :

Use what we have learned to do an exercise , Let's call today's date .

notes : You can see that I put the function under our time , Then he was also called . This shows that our function is JS China is a first-class citizen , Pre parsing will put the function at the top , So there will still be time , He will first define in execution ,, Even at the bottom , Code can also operate normally .

For the week we show, the code is a number 123..., Then we can also use our array to convert it , Get rid of ours if Judge , Directly add a group of arrays to him , We're calling xi[xingqi] The subscript of is ok .

Time stamp

The first one is : Get milliseconds , The time to the present can be calculated by the number of seconds , Timestamp is unique / Mobility ., You can get the current and past milliseconds

What can we do with timestamp ? You can get the date object with the number of milliseconds by timestamp

The second kind : Get milliseconds quickly , This method is faster than the first , But you can only get the current number of milliseconds , Cannot get the number of milliseconds of the specified date

Give me a little way . How to reflect their calculation time :

Exercises : Output current date 3 What day is next

Use Date object , Output current date 3 What day is next