The Date Object in JavaScript

The Date object in JavaScript is a global object used to handle dates and times. The Date object is based on the Unix Time Stamp, which is the number of milliseconds elapsed since 1st January 1970 UTC.

Description

The Date() constructor can accept four types of parameters: no parameters, a Unix time stamp, a time stamp string, and separate values for each date and time member. Additionally, the only way to create a new Date object is by using the new operator. If used as a regular function call, without the new operator, it will return a string instead of a Date object.

  • No parameters: If no parameters are provided, then the newly created Date object represents the date and time at the moment of instantiation.

  • Unix time stamp: A Unix time stamp is an integer value that represents the number of milliseconds elapsed since 1st January 1970 00:00:00 UTC - the Unix epoch and ignores leap seconds. Please note that most Unix time stamp functions are only accurate to the nearest second.

  • Time stamp string: A string value representing a date, which should be correctly recognized by the Date.parse() method, which means it should conform to an IETF-compliant RFC 2822 timestamp or a version of ISO8601.

  • Separate values for each date and time member: When at least the year and month are provided, this form of Date() returns a Date object with each member originating from the provided parameters. Any members not provided will default to the smallest possible value, with the date being 1 and the others being 0.

new Date();
new Date(value);
new Date(dateString);
new Date(year, monthIndex [, day [, hours [, minutes [, seconds [, milliseconds]]]]]);
console.log(new Date()); // Sun Oct 18 2020 10:46:54 GMT+0800 (China Standard Time)
console.log(new Date(1602989155183)); // Sun Oct 18 2020 10:45:55 GMT+0800 (China Standard Time)
console.log(new Date("2020-10-18 10:15:30")); // Sun Oct 18 2020 10:15:30 GMT+0800 (China Standard Time)
console.log(new Date(2020, 9, 18, 10, 15, 30)); // Sun Oct 18 2020 10:15:30 GMT+0800 (China Standard Time)
console.log(typeof(Date())); // string
console.log(typeof(new Date())); // object

Methods

Date.UTC()

Date.UTC(year,month[,date[,hrs[,min[,sec[,ms]]]]])
The Date.UTC() method accepts the same parameters as the date constructor when it accepts the maximum number of parameters and returns the number of milliseconds from 1970-1-1 00:00:00 UTC to the specified date.

  • year: A year after 1900.
  • month: An integer between 0 and 11 representing the month.
  • date: An integer between 1 and 31 representing the day of the month.
  • hrs: An integer between 0 and 23 representing the hour.
  • min: An integer between 0 and 59 representing the minute.
  • sec: An integer between 0 and 59 representing the second.
  • ms: An integer between 0 and 999 representing the millisecond.
console.log(Date.UTC(2020, 9, 18, 10, 15, 30)); // 1603016130000

Date.now()

Date.now()
The Date.now() method returns the number of milliseconds from 1st January 1970 00:00:00 (UTC) to the current time.

console.log(Date.now()); // 1602991355257

Date.parse()

Date.parse(dateString)
The Date.parse() method parses a string that represents a date. The dateString needs to conform to either RFC2822 or ISO 8601 date format strings (although other formats might be also supported, the results may not be as expected) and returns the number of milliseconds from 1970-1-1 00:00:00 UTC to the date object or the UTC time of that date object. If the string cannot be recognized, or in some cases, contains an invalid date value such as 2015-02-31, the return value is NaN. It is not recommended to use the Date.parse method before ES5, as the string parsing is entirely implementation-dependent. Even today, there are many differences in how different browsers parse date strings, so it is best to parse date strings manually or use a library, especially when adapting to different formats.

console.log(Date.parse("2020-10-18 10:15:30")); // 1602987330000 
console.log(Date.parse("2020-10-18 02:15:30 GMT")); // 1602987330000 
console.log(Date.parse("2020-10-18 02:15:30 UTC")); // 1602987330000 
console.log(Date.parse("2020-10-18 10:15:30 GMT")); // 1603016130000
console.log(Date.parse("2020-10-18 10:15:30 UTC")); // 1603016130000
console.log((1602987330000 - 1603016130000) / 1000 / 3600); // -8
// If you're in Greenwich, your epoch is `1st January 1970 00:00:00`.
// If you're in Beijing, your epoch is `1st January 1970 08:00:00`.
// For the same date and time, the timestamp in Beijing is less.
// Running Date.now() in different time zones will return the same timestamp, as the timestamp does not carry time zone information.
// If I get a timestamp t in Beijing, and in Greenwich, using new Date(t), they will be 8 hours apart.
// Alternatively, if you calculate the time using the same timestamp, the Beijing time is 8 hours ahead of Greenwich Mean Time.

Date.prototype.getDate()

dateObj.getDate()
This method returns the day of the month for the specified date according to local time. The range is from 1 to 31.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getDate()); // 18

Date.prototype.getDay()

dateObj.getDay()
The getDay() method returns the day of the week for the specified date according to local time, where 0 represents Sunday.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getDay()); // 0

Date.prototype.getFullYear()

dateObj.getFullYear()
The getFullYear() method returns the year of the specified date according to local time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getFullYear()); // 2020

Date.prototype.getHours()

dateObj.getHours()
The getHours() method returns the hour for the specified date according to local time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getHours()); // 10

Date.prototype.getMilliseconds()

dateObj.getMilliseconds()
The getMilliseconds() method returns the milliseconds for the specified date according to local time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getMilliseconds()); // 0

Date.prototype.getMinutes()

dateObj.getMinutes()
The getMinutes() method returns the minutes for the specified date according to local time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getMinutes()); // 15

Date.prototype.getMonth()

dateObj.getMonth()
This method returns the month for the specified date according to local time. The month is a number from 0 to 11 where 0 represents January.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getMonth()); // 9

Date.prototype.getSeconds()

dateObj.getSeconds()
The getSeconds() method returns the seconds for the specified date according to local time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getSeconds()); // 30

Date.prototype.getTime()

dateObj.getTime()
The getTime method returns the numeric value corresponding to the time for the specified date according to local time. This value represents the number of milliseconds since January 1, 1970, 00:00:00.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getTime()); // 1602987330000

Date.prototype.getTimezoneOffset()

dateObj.getTimezoneOffset()
The getTimezoneOffset() method returns the time difference in minutes between Coordinated Universal Time (UTC) and the current time zone.

var date = new Date();
console.log(date.getTimezoneOffset() / 60); // -8

Date.prototype.getUTCDate()

dateObj.getUTCDate()
The getUTCDate() method returns the day of the month in the specified date according to Universal Time Coordinate (UTC).

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCDate()); // 18

Date.prototype.getUTCDay()

dateObj.getUTCDay()
The getUTCDay() method returns the day of the week in the specified date according to Universal Time Coordinate (UTC), where 0 represents Sunday.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCDay()); // 0

Date.prototype.getUTCFullYear()

dateObj.getUTCFullYear()
The getUTCFullYear() method returns the year of the specified date according to Universal Time Coordinate (UTC).

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCFullYear()); // 2020

Date.prototype.getUTCHours()

dateObj.getUTCHours()
The getUTCHours() method returns the hour for the specified date according to Universal Time Coordinate (UTC).

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCHours()); // 2

Date.prototype.getUTCMilliseconds()

dateObj.getUTCMilliseconds()
The getUTCMilliseconds() method returns the milliseconds for the specified date according to Universal Time Coordinate (UTC).

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCMilliseconds()); // 0

Date.prototype.getUTCMinutes()

dateObj.getUTCMinutes()
The getUTCMinutes() method returns the minutes in a specified date object according to universal time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCMinutes()); // 15

Date.prototype.getUTCMonth()

dateObj.getUTCMonth()
The getUTCMonth() method returns the month in a specified date object according to universal time. It is zero-indexed, with 0 representing the first month of the year.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCMonth()); // 9

Date.prototype.getUTCSeconds()

dateObj.getUTCSeconds()
The getUTCSeconds() method returns the seconds in a specified date object according to universal time.

var date = new Date("2020-10-18 10:15:30");
console.log(date.getUTCSeconds()); // 30

Date.prototype.setDate()

dateObj.setDate(dayValue)
The setDate() method sets the day of a specified date object based on local time.

  • dayValue: An integer representing the day of the month.
var date = new Date("2020-10-18 10:15:30");
date.setDate(1);
console.log(date); // Thu Oct 01 2020 10:15:30 GMT+0800 (China Standard Time)

Date.prototype.setFullYear()

dateObj.setFullYear(yearValue[, monthValue[, dayValue]])
The setFullYear() method sets the year for a specified date object based on local time.

  • yearValue: An integer value for the year, for example 1995.
  • monthValue: An integer value between 0 and 11, representing January to December.
  • dayValue: An integer value between 1 and 31, representing the day of the month. If dayValue is specified, monthValue must also be specified.
var date = new Date("2020-10-18 10:15:30");
date.setFullYear(2019, 0, 1);
console.log(date); // Tue Jan 01 2019 10:15:30 GMT+0800 (China Standard Time)

Date.prototype.setHours()

dateObj.setHours(hoursValue[, minutesValue[, secondsValue[, msValue]]])
The setHours() method sets the hours for a specified date object based on local time, returning the number of milliseconds elapsed since January 1, 1970 00:00:00 UTC. Prior to JavaScript 1.3, it only accepted one parameter.

  • hoursValue: An integer between 0 and 23 representing the hour.
  • minutesValue: An integer between 0 and 59 representing the minutes.
  • secondsValue: An integer between 0 and 59 representing the seconds. If secondsValue is specified, minutesValue must also be specified.
  • msValue: A number between 0 and 999 representing the milliseconds. If msValue is specified, both minutesValue and secondsValue must also be specified.
var date = new Date("2020-10-18 10:15:30");
console.log(date.setHours(8)); // 1602980130000
console.log(date); // Sun Oct 18 2020 08:15:30 GMT+0800 (China Standard Time)

Date.prototype.setMilliseconds()

dateObj.setMilliseconds(millisecondsValue)
The setMilliseconds() method sets the milliseconds for a specified date object based on local time.

  • millisecondsValue: A number between 0 and 999 representing the milliseconds.
var date = new Date("2020-10-18 10:15:30");
date.setMilliseconds(1);
console.log(date.getMilliseconds()); // 1

Date.prototype.setMinutes()

dateObj.setMinutes(minutesValue[, secondsValue[, msValue]])
The setMinutes() method sets the minutes for a specified date object based on local time. Prior to JavaScript 1.3, it only accepted the first parameter.

  • minutesValue: An integer between 0 and 59 representing the minutes.
  • secondsValue: An integer between 0 and 59 representing the seconds. If secondsValue is specified, minutesValue must also be specified.
  • msValue: A number between 0 and 999 representing the milliseconds. If msValue is specified, both minutesValue and secondsValue must also be specified.
var date = new Date("2020-10-18 10:15:30");
date.setMinutes(1);
console.log(date); // Sun Oct 18 2020 10:01:30 GMT+0800 (China Standard Time)
### Date.prototype.setMonth()
`dateObj.setMonth(monthValue[, dayValue])`  
The `setMonth()` method sets the month for a given date object based on local time, and returns the number of milliseconds between `1970-01-01 00:00:00 UTC` and the updated date object instance. Prior to `JavaScript 1.3`, only the first parameter was accepted.

* `monthValue`: An integer between `0` and `11`, representing January to December.
* `dayValue`: An integer between `1` and `31`, representing the day of the month. `0` represents the last day of the previous month.

```javascript
var date = new Date("2020-10-18 10:15:30");
date.setMonth(1);
console.log(date); // Tue Feb 18 2020 10:15:30 GMT+0800 (China Standard Time)

Date.prototype.setSeconds()

dateObj.setSeconds(secondsValue[, msValue])
The setSeconds() method sets the seconds for a given date object based on local time. Prior to JavaScript 1.3, only the first parameter was accepted.

  • secondsValue: An integer between 0 and 59.
  • msValue: A number between 0 and 999, representing milliseconds.
var date = new Date("2020-10-18 10:15:30");
date.setSeconds(1);
console.log(date); // Sun Oct 18 2020 10:15:01 GMT+0800 (China Standard Time)

Date.prototype.setTime()

dateObj.setTime(timeValue)
The setTime() method sets the time for a Date object using the number of milliseconds from 1970-1-1 00:00:00 UTC.

  • timeValue: An integer representing the number of milliseconds from 1970-1-1 00:00:00 UTC.
var date = new Date("2020-10-18 10:15:30");
date.setTime(1603011933306);
console.log(date); // Sun Oct 18 2020 17:05:33 GMT+0800 (China Standard Time)

Date.prototype.setUTCDate()

dateObj.setUTCDate(dayValue)
The setUTCDate() method sets the date of a specific date object based on global time.

  • dayValue: An integer between 1 and 31, specifying the date.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCDate(1);
console.log(date.toUTCString()); // Thu, 01 Oct 2020 10:15:30 GMT

Date.prototype.setUTCFullYear()

dateObj.setUTCFullYear(yearValue[, monthValue[, dayValue]])
The setUTCFullYear() method sets the year for a specific date based on Coordinated Universal Time (UTC). Prior to JavaScript 1.3, only the first parameter was accepted.

  • yearValue: An integer specifying the year, for example, 1995.
  • monthValue: An integer between 0 and 11, representing January to December.
  • dayValue: An integer between 1 and 31, representing the day of the month. If dayValue is specified, monthValue must also be specified.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCFullYear(2019);
console.log(date.toUTCString()); // Fri, 18 Oct 2019 10:15:30 GMT

Date.prototype.setUTCHours()

dateObj.setUTCHours(hoursValue[, minutesValue[, secondsValue[, msValue]]])
The setUTCHours() method sets the hour for a specific date based on Coordinated Universal Time (UTC), and returns the number of milliseconds between 1970-1-1 00:00:00 UTC and the updated date instance.

  • hoursValue: An integer representing the hour, between 0 and 23.
  • minutesValue: An integer representing the minutes, between 0 and 59.
  • secondsValue: An integer representing the seconds, between 0 and 59. If this parameter is specified, minutesValue must also be specified.
  • msValue: An integer representing the milliseconds, between 0 and 999. If this parameter is specified, both minutesValue and secondsValue must be specified.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCHours(1);
console.log(date.toUTCString()); // Sun, 18 Oct 2020 01:15:30 GMT

Date.prototype.setUTCMilliseconds()

dateObj.setUTCMilliseconds(millisecondsValue)
The setUTCMilliseconds() method sets the milliseconds of a specific time based on Coordinated Universal Time (UTC).

  • millisecondsValue: A value between 0 and 999, representing milliseconds.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCMilliseconds(111);
console.log(date.getUTCMilliseconds()); // 111

Date.prototype.setUTCMinutes()

dateObj.setUTCMinutes(minutesValue[, secondsValue[, msValue]])
The setUTCMinutes() method sets the minutes for a specified date according to Coordinated Universal Time (UTC), returning the number of milliseconds between the date and midnight of January 1, 1970.

  • minutesValue: Represents the minutes to be set and is an integer between 0 and 59.
  • secondsValue: Represents the seconds to be set, also an integer between 0 and 59. If this parameter is passed, the previous parameter minutesValue must also be passed.
  • msValue: Represents the milliseconds to be set, a number between 0 and 999. If this parameter is passed, the previous two parameters minutesValue and secondsValue must also be passed.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCMinutes(1);
console.log(date.toUTCString()); // Sun, 18 Oct 2020 10:01:30 GMT

Date.prototype.setUTCMonth()

dateObj.setUTCMonth(monthValue[, dayValue])
The setUTCMonth() method sets an exact month according to Coordinated Universal Time (UTC), returning the number of milliseconds between the date and midnight of January 1, 1970.

  • monthValue: An integer from 0 to 11, representing January to December.
  • dayValue: An integer from 1 to 31, representing the day of the month.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCMonth(1);
console.log(date.toUTCString()); // Tue, 18 Feb 2020 10:15:30 GMT

Date.prototype.setUTCSeconds()

dateObj.setUTCSeconds(secondsValue[, msValue])
The setUTCSeconds() method sets the seconds for a specific date according to Coordinated Universal Time (UTC), returning the number of milliseconds between the date and midnight of January 1, 1970.

  • secondsValue: An integer between 0 and 59 representing the seconds.
  • msValue: A number between 0 and 999, representing the milliseconds.
var date = new Date("2020-10-18 10:15:30 GMT");
date.setUTCSeconds(1);
console.log(date.toUTCString()); // Sun, 18 Oct 2020 10:15:01 GMT

Date.prototype.toDateString()

dateObj.toDateString()
The toDateString() method returns the date portion of a date object as a string.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toDateString()); // Sun Oct 18 2020

Date.prototype.toISOString()

dateObj.toISOString()
The toISOString() method returns a string in the ISO 8601 Extended Format format YYYY-MM-DDTHH:mm:ss.sssZ, where the timezone is always Coordinated Universal Time (UTC), marked with a suffix Z.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toISOString()); // 2020-10-18T02:15:30.000Z

Date.prototype.toJSON()

dateObj.toJSON()
The toJSON() method returns the string form of the Date object, calling toJSON() returns a string in JSON format using toISOString(), representing the value of the date object. By default, this method is commonly used for JSON serialization of Date objects.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toJSON()); // 2020-10-18T02:15:30.000Z

Date.prototype.toLocaleDateString()

dateObj.toLocaleDateString([locales [, options]])
The toLocaleDateString() method returns a string representing the date portion of the date object. The format of the string varies by language. The addition of the locales and options parameters allows the program to specify which language formatting rules to use, allowing customization of the method's behavior. In older browser versions, the locales and options parameters are ignored, and the language environment and returned string format are independently implemented.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toLocaleDateString()); // 2020/10/18

Date.prototype.toLocaleString()

dateObj.toLocaleString([locales [, options]])
The toLocaleString() method returns a string representing the date object. The format of the string varies by language. The addition of the locales and options parameters allows the program to specify which language formatting rules to use, allowing customization of the method's behavior. In older browser versions, the locales and options parameters are ignored, and the language environment and returned string format are independently implemented.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toLocaleString()); // 2020/10/18 上午10:15:30

Date.prototype.toLocaleTimeString()

dateObj.toLocaleTimeString([locales [, options]])
The toLocaleTimeString() method returns a string representing the time portion of the given date object. The format of the string may vary depending on the language. The newly added locales and options parameters allow the program to specify which language formatting rules to use, allowing customization of the behavior of this method. In older versions of browsers, the locales and options parameters are ignored, and the language environment used and the format of the returned string are independently implemented.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toLocaleTimeString()); // 上午10:15:30

Date.prototype.toString()

dateObj.toString()
The toString() method returns a string representing the Date object.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toString()); // Sun Oct 18 2020 10:15:30 GMT+0800 (China Standard Time)

Date.prototype.toTimeString()

dateObj.toTimeString()
The toTimeString() method returns a string representing the time portion of a date object.

var date = new Date("2020-10-18 10:15:30");
console.log(date.toTimeString()); // 10:15:30 GMT+0800 (China Standard Time)

Date.prototype.toUTCString()

dateObj.toUTCString()
The toUTCString() method converts a date to a string using the UTC time zone.

var date = new Date("2020-10-18 10:15:30 GMT");
console.log(date.toUTCString()); // Sun, 18 Oct 2020 10:15:30 GMT

Date.prototype.valueOf()

dateObj.valueOf()
The valueOf() method returns the primitive value of a Date object.

var date = new Date("2020-10-18 10:15:30");
console.log(date.valueOf()); // 1602987330000

Date.prototype[@@toPrimitive]

Date()[Symbol.toPrimitive]()
The [@@toPrimitive]() method converts a Date object to a primitive value. If the hint is "string" or "default", [@@toPrimitive]() will call toString, and if the toString property does not exist, it will call valueOf. If valueOf also does not exist, it will throw a TypeError. If the hint is "number", [@@toPrimitive]() will first try valueOf, and if that fails, it will try toString. When an object is received instead of a primitive value, JavaScript can automatically call the [@@toPrimitive]() method to convert the object to a primitive value, so you rarely need to call this method yourself.

var date = new Date("2020-10-18 10:15:30");
console.log(date[Symbol.toPrimitive]("string")); // Sun Oct 18 2020 10:15:30 GMT+0800 (China Standard Time)

Daily question

https://github.com/WindrunnerMax/EveryDay

Reference

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
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