Common methods and applications of JavaScript date objects

I feel like this title is too big

In fact, date objects are not commonly used, and there don’t seem to be many applications
But we need to understand some basic usage

Date object

Date date object is the native js constructor
Unlike arrays, objects, etc., it has no corresponding constant form
Creating a date object is very simple

var date = new Date();

Date() can take parameters (string), specify the date and time like this

console.log(new Date("2016/1/1"));

Without parameters, the current date and time are used

Date() is mainly used to obtain the current Timestamp (number of milliseconds since January 1, 1970)
This value can be obtained through the getTime method of the date object

Let’s take a look at the commonly used methods of obtaining date objects

• getFullYear() Get the year

• getMonth() Get the month

• ##getDate() Get the number of days

• getDay() Get the day of the week

• getHours() Get the hours

• getMinutes() Get the minutes

• getSeconds() Get seconds

• getTime() Get timestamp

If you want to set the date object, put the previous Get has been changed to set, and I feel that it is not necessary.

The thing to note is not to use getYear(), because it returns the year difference from 1900, and no one uses it
There is also the getMonth() method The returned month starts from zero, that is, 0 to 11, representing January to December.
The range of getDay() is 0 to 6, 0 represents Sunday.
Let’s practice encapsulating a function to print the current date information.
Look at the table, today is 18:45 on November 6, 2016

function getCurrentDate(){    var date = new Date();
    console.log('年份：' + date.getFullYear(),                
    '月份：' + (date.getMonth() + 1),                
    '天数：' + date.getDate(),                
    '小时：' + date.getHours(),                
    '分钟：' + date.getMinutes(),                
    '秒数：' + date.getSeconds());
}
getCurrentDate();

Console printing:

If you do not use new, call Date() directly, What is returned is a string of date information

Date There is another static method to mention is parse(), which is very similar to getTime()

The definition given by w3c: returns January 1, 1970 The number of milliseconds from midnight to the specified date (string)
Use this way

Application

In fact, there are not many applications for date objects

It is nothing more than getting the current date, Performance test
To get the current date, just instantiate a date object directly, and then call the method

Performance test is to use timestamp/time cutoff

function loop(){
    for(var i = 0; i < 1000; i++){
        console.log(1);
    }
}var timeStart = new Date().getTime();
loop();var timeEnd = new Date().getTime();
console.log(&#39;程序运行时间：&#39; + (timeEnd - timeStart));

This code is my test loop function How long did it take to run?

Or you can use the method I used in the JavaScript single-threaded underlying principle

function loop(){
    for(var i = 0; i < 1000; i++){
        console.log(1);
    }
}var timeStart = +new Date();
loop();var timeEnd = +new Date();
console.log(&#39;程序运行时间：&#39; + (timeEnd - timeStart));

The effect is the same, but it is not recommended to use forced type conversion for date types.

The plus sign is equivalent to the implicit conversion of the instantiated date object into a number
That is, calling the valueOf() overridden by the Date object

The new date object static method now in ES5 () is more convenient. Get the current timestamp directly

function loop(){
    for(var i = 0; i < 1000; i++){
        console.log(1);
    }
}var timeStart = Date.now();
loop();var timeEnd = Date.now();
console.log(&#39;程序运行时间：&#39; + (timeEnd - timeStart));

We can also write a polyfill (supplementary code/padding code) for older versions of browsers

if(!Date.now){    Date.now = function(){
        return new Date().getTime();
    }
}

The above is the JavaScript date object Commonly used methods and applications, please pay attention to the PHP Chinese website (www.php.cn) for more related content!