How to convert date in javascript

In web development, date processing is often required, including date format conversion. In JavaScript, you can use the built-in Date object and some methods to convert dates.

1. Creation of Date Object

To create a date object, you can use the Date() constructor, with or without parameters. Without parameters, the current date and time will be automatically obtained.

var date = new Date(); //获取当前日期和时间

If you want to create a date object that specifies the date and time, you can pass in parameters such as year, month, day, hour, minute, and second.

var date = new Date(2022, 0, 1, 12, 0, 0); //创建2022年1月1日12:00:00的日期对象

Among them, the month starts counting from 0, so 0 represents January, 1 represents February, and so on. Hours are in 24-hour format.

2. Conversion of date format

JavaScript provides multiple methods to convert date format, we will introduce them separately below.

(1) Convert date object to string

You can convert date object to string by calling the toString() method of Date object.

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

The output results are as follows:

Tue Oct 19 2021 17:22:48 GMT+0800 (中国标准时间)

(2) Convert date object to timestamp

The timestamp refers to since January 1, 1970 00:00:00 UTC The number of seconds since. You can get the timestamp of a date object by calling the getTime() method of the Date object.

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

The output results are as follows:

1634640291737

(3) Convert timestamp to date object

Can be created by calling the constructor of the Date object and passing in a timestamp parameter A date object.

var timestamp = 1634640291737;
var date = new Date(timestamp);
console.log(date.toString());

The output results are as follows:

Tue Oct 19 2021 17:24:51 GMT+0800 (中国标准时间)

(4) Convert the date object to a string in the specified format

To format a date object into the specified string format, You can use some other methods of the Date object, such as getFullYear(), getMonth(), getDate(), getHours(), getMinutes(), getSeconds() and other methods to obtain the year, month, day, hour, minute, and second of the date object. Wait for the information, and then use string concatenation to construct a string that meets the requirements.

For example, to format a date object into the format of "yyyy-MM-dd hh:mm:ss", you can use the following code:

function formatDate(date) {
    var year = date.getFullYear(),
        month = date.getMonth() + 1,
        day = date.getDate(),
        hour = date.getHours(),
        minute = date.getMinutes(),
        second = date.getSeconds();
    return year + "-" + formatNumber(month) + "-" + formatNumber(day) + " " + formatNumber(hour) + ":" + formatNumber(minute) + ":" + formatNumber(second);
}

function formatNumber(number) {
    return number < 10 ? "0" + number : number;
}

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

The output result is as follows:

2021-10-19 17:31:51

3. Date operation

In JavaScript, date objects can be added and subtracted. For example, you can use the following method to calculate the number of days difference between two date objects.

function dateDiffInDays(date1, date2) {
    var timeDiff = date2.getTime() - date1.getTime();
    var dayDiff = timeDiff / (1000 * 3600 * 24);
    return Math.floor(dayDiff);
}

var date1 = new Date(2021, 0, 1);
var date2 = new Date(2021, 9, 19);
console.log(dateDiffInDays(date1, date2));

The output result is:

291

4. Summary

In JavaScript, you can use the Date object to handle dates and their format conversion. To create a date object, use the Date() constructor. To convert a date object to a string, you can use the toString() method. To convert a date object to a timestamp, you can use the getTime() method. To convert a timestamp to a date object, you can use the Date() constructor and pass in the timestamp parameter. To format a date object into a string in a specified format, you can use other methods to obtain the year, month, day, hour, minute, second and other information of the date object, and then use string concatenation to construct a string that meets the requirements. Date objects can also be added and subtracted.

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