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Formatting Dates With the DateTimeFormat Object

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Different parts of the world have different date formats. To deal with this, JavaScript has the Intl.DateTimeFormat constructor to let us format dates into different formats according to different locales.

This means that we can format dates for different places without manipulating date strings ourselves, making our lives much easier. The Intl.DateTimeFormat constructor takes a locale string as the argument.

With the DateTimeFormat constructed with the constructor, we can use the format instance method, which takes in a Date object to return a date string with the date formatted for the locale you specified in the Intl.DateTimeFormat constructor.


The Constructor and the Format Method

To use the Intl.DateTimeFormat constructor, we can use it like in the following example:

const date = new Date(2019, 0, 1, 0, 0, 0);  
console.log(new Intl.DateTimeFormat('en-US').format(date));  
console.log(new Intl.DateTimeFormat('fr-ca').format(date));  
console.log(new Intl.DateTimeFormat(['ban', 'de']).format(date));

In the above example, we created the Date object, and then we used the Intl.DateTimeFormat constructor with one or more locales passed in as a string.

Then, we called format by passing in the Date object. The first example would log 1/1/2019 since the United States use the MM/DD/YYYY date format.

The second example would log 2019–01–01 since French Canadian dates are in YYYY-MM-DD format. The third example takes an array where there are multiple locales, the ones further to the right are the fallback locales for the ones for the left.

In our example, since we have an invalid locale string ban in the first entry of the array, we use the German date format de instead, to format the Date object, so we get 1.1.2019 since Germany uses the DD.MM.YYYY date format.

As we can see from the examples above, the Intl.DateTimeFormat constructor takes a locale string or an array of locale strings. It also accepts Unicode extension keys for locale strings, so that we can append them to our language tag.

The extension keys nu for setting the numbering system, ca for the calendar to format the date, and hc for the hour cycle are supported.

nu’s possible values can be arab, arabext, bali, beng, deva, fullwide, gujr, guru, hanidec, khmr, knda, laoo, latn, limb, mlym, mong, mymr, orya, tamldec, telu, thai, tibt.

ca’s possible values include buddhist, chinese, coptic, ethiopia, ethiopic, gregory, hebrew, indian, islamic, iso8601, japanese, persian, roc.

hc’s possible values include h11, h12, h23, h24. For example, to format dates according to the Buddhist calendar, we can write:

const date = new Date(2019, 0, 1, 0, 0, 0);  
console.log(new Intl.DateTimeFormat('en-US-u-ca-buddhist').format(date));

Then we get 1/1/2562 in the console.log since the Buddhist calendar’s year 0 is at 545 BC.

The second argument takes an object that lets us set various options in its properties to format the date.

The localeMatcher option specifies the locale-matching algorithm to use. The possible values are lookup and best fit. The lookup algorithm searches for the locale until it finds the one that fits the character set of the strings that are being compared.

best fit finds the locale that is at least, but possibly more, suited than the lookup algorithm. The timeZone option lets us set the time zone which formats the date.

The most basic implementation only recognizes UTC, but others may recognize IANA time zone names in the IANA time zone data database, like Asia/Shanghai, Asia/Kolkata, America/New_York.

The hour12 option specifies whether the format is for 12-hour time or 24-hour time. The default is locale dependent. It overrides the hc language tag in the first argument.

It’s a true or false value where true means format the date time with 12-hour time. The hourCycle option has possible values of h11, h12, h23, h24 and overrides the hc language tag. hour12 takes precedence over this option if it’s specified.

The formatMatcher property specifies the matching algorithm to use. Possible values are basic and best fit. best fit is the default value.

The following subsets of the date time are required to match the date object to the correct format:

  • weekday, year, month, day, hour, minute, second
  • weekday, year, month, day
  • year, month, day
  • year, month
  • month, day
  • hour, minute, second
  • hour, minute

weekday represents the weekday value, possible values are:

  • long (e.g., Friday)
  • short (e.g., Fri)
  • “narrow" (e.g., T). Note that two weekdays may have the same narrow style for some locales. For example, Tuesday‘s narrow style is also T.

era represents the era, possible values are:

  • long (e.g., Anno Domini)
  • short (e.g., AD)
  • narrow (e.g., A)

year represents the year. The possible values are:

  • numeric (e.g., 2019)
  • 2-digit (e.g., 19)

month is the representation of the month. The possible values are:

  • numeric (e.g., 2)
  • 2-digit (e.g., 02)
  • long (e.g., February)
  • short (e.g., Feb)
  • narrow (e.g., M). Note that two months may have the same narrow style for some locales (e.g. May‘s narrow style is also M).

day represents the day. Possible values are:

  • numeric (e.g., 2)
  • 2-digit (e.g., 02)

hour is the representation of the hour. The possible values are numeric, 2-digit.

minute is the representation of the minute. The possible values are numeric, 2-digit.

second is the representation of the second. The possible values are numeric, 2-digit.

timeZoneName is the representation of the time zone name. The possible values are:

  • long (e.g., Pacific Standard Time)
  • short (e.g., GMT-8)

The default value for each component property above is undefined, but if all components are undefined then the year, month, and day are assumed to be numeric.

An example for using the options is below:

const date = new Date(2019, 0, 1, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric'  
};  
console.log(new Intl.DateTimeFormat('en-ca', options).format(date));

In the code above, we set the locale to Canadian English, and in the options object we set weekday to long, year to numeric, month to long, and day to numeric, so that we get the full weekday name in English, year as a number, month with the full name, and day as a number.

The console.log will log “Tuesday, January 1, 2019”. The example above can have a time zone added to it, as in the following example:

const date = new Date(2019, 0, 1, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
console.log(new Intl.DateTimeFormat('en-ca', options).format(date));

In the example above, we added the timeZone and timeZoneLong so that we get the time zone displayed, so that we get “Tuesday, January 1, 2019, Pacific Standard Time”.

The Intl.DateTimeFormat constructor handles non-English format equally well. For example, if we want to format a date into Chinese, we can change the locale and keep the options the same as above like in the following code:

const date = new Date(2019, 0, 1, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
console.log(new Intl.DateTimeFormat('zh-Hant', options).format(date));

Then, we get “2019年1月1日 星期二 太平洋標準時間”, which is the same as “Tuesday, January 1, 2019, Pacific Standard Time” in traditional Chinese.


Other Instance Methods

Instances of the Intl.DateTimeFormat constructor object also have a few instance methods in addition to the format() method.

It also has the formatToParts() method to return an array of objects representing different parts of the date string. The resolvedOptions() method returns a new object with properties that reflect the locale and formatting options that we computed during the initialization of the object.

The formatRange() method accepts two Date objects as arguments and formats the date range in the most concise way, based on the locale and options provided when we instantiate the DateTimeFormat object.

Finally, it has the formatRangeToParts() method which accepts two Date objects as arguments and formats the date range in the most concise way based on the locale and options provided when we instantiate the DateTimeFormat object and return the date time parts in an array of objects.

For example, if we have the following code that calls the formatRangeToParts() method:

const startDate = new Date(2019, 0, 1, 0, 0, 0);  
const endDate = new Date(2019, 0, 2, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
const dateRange = new Intl.DateTimeFormat('zh-Hant', options).formatRangeToParts(startDate, endDate)  
console.log(dateRange);

Then we get the following date and time parts logged:

[  
  {  
    "type": "year",  
    "value": "2019",  
    "source": "startRange"  
  },  
  {  
    "type": "literal",  
    "value": "年",  
    "source": "startRange"  
  },  
  {  
    "type": "month",  
    "value": "1",  
    "source": "startRange"  
  },  
  {  
    "type": "literal",  
    "value": "月",  
    "source": "startRange"  
  },  
  {  
    "type": "day",  
    "value": "1",  
    "source": "startRange"  
  },  
  {  
    "type": "literal",  
    "value": "日 ",  
    "source": "startRange"  
  },  
  {  
    "type": "weekday",  
    "value": "星期二",  
    "source": "startRange"  
  },  
  {  
    "type": "literal",  
    "value": " ",  
    "source": "startRange"  
  },  
  {  
    "type": "timeZoneName",  
    "value": "太平洋標準時間",  
    "source": "startRange"  
  },  
  {  
    "type": "literal",  
    "value": " – ",  
    "source": "shared"  
  },  
  {  
    "type": "year",  
    "value": "2019",  
    "source": "endRange"  
  },  
  {  
    "type": "literal",  
    "value": "年",  
    "source": "endRange"  
  },  
  {  
    "type": "month",  
    "value": "1",  
    "source": "endRange"  
  },  
  {  
    "type": "literal",  
    "value": "月",  
    "source": "endRange"  
  },  
  {  
    "type": "day",  
    "value": "2",  
    "source": "endRange"  
  },  
  {  
    "type": "literal",  
    "value": "日 ",  
    "source": "endRange"  
  },  
  {  
    "type": "weekday",  
    "value": "星期三",  
    "source": "endRange"  
  },  
  {  
    "type": "literal",  
    "value": " ",  
    "source": "endRange"  
  },  
  {  
    "type": "timeZoneName",  
    "value": "太平洋標準時間",  
    "source": "endRange"  
  }  
]

As we can see from the console output above, we get the date and time parts in each entry of the array, with the parts of the startDate coming first and the endDate parts being in the latter parts of the array.

If we call the formatRange() method, like in the code below:

const startDate = new Date(2019, 0, 1, 0, 0, 0);  
const endDate = new Date(2019, 0, 2, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
const dateRange = new Intl.DateTimeFormat('en', options).formatRange(startDate, endDate)  
console.log(dateRange);

Then we get:

"Tuesday, January 1, 2019, Pacific Standard Time – Wednesday, January 2, 2019, Pacific Standard Time"

From the console.log.

To call the resolvedOptions method, we can write the code below:

const date = new Date(2019, 0, 1, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
const resolvedOptions = new Intl.DateTimeFormat('en', options).resolvedOptions(date)  
console.log(resolvedOptions);

Then we get the options that we passed in for formatting the date back:

{  
  "locale": "en",  
  "calendar": "gregory",  
  "numberingSystem": "latn",  
  "timeZone": "America/Vancouver",  
  "weekday": "long",  
  "year": "numeric",  
  "month": "long",  
  "day": "numeric",  
  "timeZoneName": "long"  
}

In the console.log.

To use the formatToParts() method, we can use it like the format() method, like in the following code:

const date = new Date(2019, 0, 1, 0, 0, 0);  
const options = {  
  weekday: 'long',  
  year: 'numeric',  
  month: 'long',  
  day: 'numeric',  
  timeZone: 'America/Vancouver',  
  timeZoneName: 'long'  
};  
const dateParts = new Intl.DateTimeFormat('en', options).formatToParts(date)  
console.log(dateParts);

Then we get the parts of the formatted date in the console.log like in the output below:

[  
  {  
    "type": "weekday",  
    "value": "Tuesday"  
  },  
  {  
    "type": "literal",  
    "value": ", "  
  },  
  {  
    "type": "month",  
    "value": "January"  
  },  
  {  
    "type": "literal",  
    "value": " "  
  },  
  {  
    "type": "day",  
    "value": "1"  
  },  
  {  
    "type": "literal",  
    "value": ", "  
  },  
  {  
    "type": "year",  
    "value": "2019"  
  },  
  {  
    "type": "literal",  
    "value": ", "  
  },  
  {  
    "type": "timeZoneName",  
    "value": "Pacific Standard Time"  
  }  
]

As we can see, the Intl.DateTimeFormat constructor is very useful for formatting dates for different locales. It eliminates a lot of hassle when formatting dates.

The constructor takes one or more locales as the first argument and a variety of options as the second argument.

It can format dates into one string and also format them and break them up into parts. This saves a lot of hassle when formatting dates for different regions since we don’t have to do any date string manipulation.

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