d3/docs/d3-time-format.md

d3-time-format

This module provides an approximate JavaScript implementation of the venerable strptime and strftime functions from the C standard library, and can be used to parse or format dates in a variety of locale-specific representations. To format a date, create a formatter from a specifier (a string with the desired format directives, indicated by %); then pass a date to the formatter, which returns a string. For example, to convert the current date to a human-readable string:

const formatTime = d3.utcFormat("%B %d, %Y");
formatTime(new Date()); // "May 31, 2023"

Likewise, to convert a string back to a date, create a parser:

const parseTime = d3.utcParse("%B %d, %Y");
parseTime("June 30, 2015"); // 2023-05-31

You can implement more elaborate conditional time formats, too. For example, here’s a multi-scale time format using time intervals:

const formatMillisecond = d3.utcFormat(".%L"),
    formatSecond = d3.utcFormat(":%S"),
    formatMinute = d3.utcFormat("%I:%M"),
    formatHour = d3.utcFormat("%I %p"),
    formatDay = d3.utcFormat("%a %d"),
    formatWeek = d3.utcFormat("%b %d"),
    formatMonth = d3.utcFormat("%B"),
    formatYear = d3.utcFormat("%Y");

function multiFormat(date) {
  return (d3.utcSecond(date) < date ? formatMillisecond
      : d3.utcMinute(date) < date ? formatSecond
      : d3.utcHour(date) < date ? formatMinute
      : d3.utcDay(date) < date ? formatHour
      : d3.utcMonth(date) < date ? (d3.utcWeek(date) < date ? formatDay : formatWeek)
      : d3.utcYear(date) < date ? formatMonth
      : formatYear)(date);
}

This module is used by D3 time scales to generate human-readable ticks.

Also see date.toLocaleString.

timeFormat(specifier)

d3.timeFormat("%b %d")

An alias for locale.format on the default locale.

timeParse(specifier)

d3.timeParse("%b %d")

An alias for locale.parse on the default locale.

utcFormat(specifier)

d3.utcFormat("%b %d")

An alias for locale.utcFormat on the default locale.

utcParse(specifier)

d3.utcParse("%b %d")

An alias for locale.utcParse on the default locale.

isoFormat

d3.isoFormat(new Date()) // "2023-05-31T18:17:36.788Z"

Source · The full ISO 8601 UTC time formatter. Where available, this method will use Date.toISOString to format.

isoParse

d3.isoParse("2023-05-31T18:17:36.788Z")

Source · The full ISO 8601 UTC time parser. Where available, this method will use the Date constructor to parse strings. If you depend on strict validation of the input format according to ISO 8601, you should construct a UTC parser function:

const strictIsoParse = d3.utcParse("%Y-%m-%dT%H:%M:%S.%LZ");

locale.format(specifier)

d3.timeFormat("%b %d")

Source · Returns a new formatter for the given string specifier. The specifier string may contain the following directives:

• %a - abbreviated weekday name.*
• %A - full weekday name.*
• %b - abbreviated month name.*
• %B - full month name.*
• %c - the locale’s date and time, such as %x, %X.*
• %d - zero-padded day of the month as a decimal number [01,31].
• %e - space-padded day of the month as a decimal number [ 1,31]; equivalent to %_d.
• %f - microseconds as a decimal number [000000, 999999].
• %g - ISO 8601 week-based year without century as a decimal number [00,99].
• %G - ISO 8601 week-based year with century as a decimal number.
• %H - hour (24-hour clock) as a decimal number [00,23].
• %I - hour (12-hour clock) as a decimal number [01,12].
• %j - day of the year as a decimal number [001,366].
• %m - month as a decimal number [01,12].
• %M - minute as a decimal number [00,59].
• %L - milliseconds as a decimal number [000, 999].
• %p - either AM or PM.*
• %q - quarter of the year as a decimal number [1,4].
• %Q - milliseconds since UNIX epoch.
• %s - seconds since UNIX epoch.
• %S - second as a decimal number [00,61].
• %u - Monday-based (ISO 8601) weekday as a decimal number [1,7].
• %U - Sunday-based week of the year as a decimal number [00,53].
• %V - ISO 8601 week of the year as a decimal number [01, 53].
• %w - Sunday-based weekday as a decimal number [0,6].
• %W - Monday-based week of the year as a decimal number [00,53].
• %x - the locale’s date, such as %-m/%-d/%Y.*
• %X - the locale’s time, such as %-I:%M:%S %p.*
• %y - year without century as a decimal number [00,99].
• %Y - year with century as a decimal number, such as 1999.
• %Z - time zone offset, such as -0700, -07:00, -07, or Z.
• %% - a literal percent sign (%).

Directives marked with an asterisk (*) may be affected by the locale definition.

For %U, all days in a new year preceding the first Sunday are considered to be in week 0. For %W, all days in a new year preceding the first Monday are considered to be in week 0. Week numbers are computed using interval.count. For example, 2015-52 and 2016-00 represent Monday, December 28, 2015, while 2015-53 and 2016-01 represent Monday, January 4, 2016. This differs from the ISO week date specification (%V), which uses a more complicated definition!

For %V,%g and %G, per the strftime man page:

In this system, weeks start on a Monday, and are numbered from 01, for the first week, up to 52 or 53, for the last week. Week 1 is the first week where four or more days fall within the new year (or, synonymously, week 01 is: the first week of the year that contains a Thursday; or, the week that has 4 January in it). If the ISO week number belongs to the previous or next year, that year is used instead.

The % sign indicating a directive may be immediately followed by a padding modifier:

• 0 - zero-padding
• _ - space-padding
• - - disable padding

If no padding modifier is specified, the default is 0 for all directives except %e, which defaults to _. (In some implementations of strftime and strptime, a directive may include an optional field width or precision; this feature is not yet implemented.)

The returned function formats a specified date, returning the corresponding string.

const formatMonth = d3.timeFormat("%B"),
    formatDay = d3.timeFormat("%A"),
    date = new Date(2014, 4, 1); // Thu May 01 2014 00:00:00 GMT-0700 (PDT)

formatMonth(date); // "May"
formatDay(date); // "Thursday"

locale.parse(specifier)

d3.timeParse("%b %d")

Source · Returns a new parser for the given string specifier. The specifier string may contain the same directives as locale.format. The %d and %e directives are considered equivalent for parsing.

The returned function parses a specified string, returning the corresponding date or null if the string could not be parsed according to this format’s specifier. Parsing is strict: if the specified string does not exactly match the associated specifier, this method returns null. For example, if the associated specifier is %Y-%m-%dT%H:%M:%SZ, then the string "2011-07-01T19:15:28Z" will be parsed as expected, but "2011-07-01T19:15:28", "2011-07-01 19:15:28" and "2011-07-01" will return null. (Note that the literal Z here is different from the time zone offset directive %Z.) If a more flexible parser is desired, try multiple formats sequentially until one returns non-null.

locale.utcFormat(specifier)

d3.utcFormat("%b %d")

Source · Equivalent to locale.format, except all directives are interpreted as Coordinated Universal Time (UTC) rather than local time.

locale.utcParse(specifier)

d3.utcParse("%b %d")

Source · Equivalent to locale.parse, except all directives are interpreted as Coordinated Universal Time (UTC) rather than local time.

timeFormatLocale(definition)

const enUs = d3.timeFormatLocale({
  dateTime: "%x, %X",
  date: "%-m/%-d/%Y",
  time: "%-I:%M:%S %p",
  periods: ["AM", "PM"],
  days: ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"],
  shortDays: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"],
  months: ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
  shortMonths: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
});

Source · Returns a locale object for the specified definition with locale.format, locale.parse, locale.utcFormat, locale.utcParse methods. The definition must include the following properties:

• dateTime - the date and time (%c) format specifier (e.g., "%a %b %e %X %Y").
• date - the date (%x) format specifier (e.g., "%m/%d/%Y").
• time - the time (%X) format specifier (e.g., "%H:%M:%S").
• periods - the A.M. and P.M. equivalents (e.g., ["AM", "PM"]).
• days - the full names of the weekdays, starting with Sunday.
• shortDays - the abbreviated names of the weekdays, starting with Sunday.
• months - the full names of the months (starting with January).
• shortMonths - the abbreviated names of the months (starting with January).

timeFormatDefaultLocale(definition)

const enUs = d3.timeFormatDefaultLocale({
  dateTime: "%x, %X",
  date: "%-m/%-d/%Y",
  time: "%-I:%M:%S %p",
  periods: ["AM", "PM"],
  days: ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"],
  shortDays: ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"],
  months: ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"],
  shortMonths: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"]
});

Source · Equivalent to d3.timeFormatLocale, except it also redefines d3.timeFormat, d3.timeParse, d3.utcFormat and d3.utcParse to the new locale’s locale.format, locale.parse, locale.utcFormat and locale.utcParse. If you do not set a default locale, it defaults to U.S. English.