JavaScript Introduction | Standard Objects | Date Methods

Date.now() Method

The Date.now() method returns the time from January 1, 1970 00:00:00 to the present as an integer in milliseconds.

var nowMiliSec = Date.now();
nowMiliSec;           // milliseconds from January 1, 1970 00:00:00 to now
new Date(nowMiliSec); // returns the same result as new Date().
new Date();

Date.prototype getter Methods

Every Date instance inherits methods and properties from Date.prototype.

Date.prototype getter methods are methods for retrieving date-related information. The most commonly used representative getter methods are as follows.

1. getFullYear()
2. getDate()
3. getDay()
4. getTime()

getFullYear() Method

The getFullYear() method returns the current year as a four-digit number (YYYY).

var date = new Date();
document.write("This year is " + date.getFullYear() + "."); // returns the current year.

getDate() Method

The getDate() method returns the number corresponding to the current day of the month.

var date = new Date();
document.write("Today is " + date.getMonth() + "/" + date.getDate() + "."); // returns the current date.

getDay() Method

The getDay() method returns the number corresponding to the current day of the week.

In JavaScript, a week starts with Sunday (0) and ends with Saturday (6).

var date = new Date();
var day;
switch (date.getDay()) { // returns the current day of the week.
    case 0:
        day = "Sun";
        break;
    case 1:
        day = "Mon";
        break;
    ...
    case 6:
        day = "Sat";
        break;
}
document.write("Today is " + day + ".");

Using an array lets you output the day of the week more simply.

var date = new Date();
var days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
document.write("Today is " + days[date.getDay()] + ".");

getTime() Method

The getTime() method returns the time from January 1, 1970 00:00:00 to the present converted to milliseconds as a number.

var date = new Date();
var period = date.getTime() / 86400000 // one day is calculated as 86,400,000 milliseconds.
document.write(period.toFixed() + " days have passed since January 1, 1970."); // omits the decimal part.

JavaScript Date.prototype getter Methods

JavaScript Date.prototype UTC getter Methods

Date.prototype setter Methods

Date.prototype setter methods are methods for setting date-related information. The most commonly used representative setter methods are as follows.

1. setFullYear()
2. setDate()

setFullYear() Method

The setFullYear() method sets the value of a Date object to a specific date.

var date = new Date();
date.setFullYear(1982, 1, 19); // February is 1 in JavaScript.
date.getFullYear();            // 1982
date.getMonth();               // 1
date.getDate();                // 19

setDate() Method

The setDate() method sets the day value of a Date object to a specific day.

var date = new Date();
date.setDate(10);              // sets the day value of the Date object to the 10th.
document.write(date + "<br>");
date.setDate(40);              // setting day 40 moves to the next month by the excess days.
document.write(date);

JavaScript Date.prototype setter Methods

There is no setDay() method in JavaScript.

JavaScript Date.prototype UTC setter Methods