Numbers

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Number Literals

• Decimal numbers: 42, 0.42
• Exponential notation: 4.2e-10
• Hexadecimal: 0x2A
• Binary: 0b101010
• Octal: 0o52
  • Old-style octal syntax invalid in strict mode: 052
• parseInt, toString have optional base argument (between 2 and 36):
  • (1000).toString(16) // '3E8'
  • parseInt('3E8', 16) // '1000'
• 0. -0 are considered different by a few functions (Object.is)
• Infinity, -Infinity, NaN

Number Functions and Methods

• Static Number functions isFinite, isNaN
  • Do not use the global functions isFinite, isNaN
  • These functions convert other types to numbers first: isNaN('Fred'), isFinite([0]) are true
• Global functions parseFloat, parseInt, also in Number.
• Static Number functions isInteger, isSafeInteger
• Number instance methods for floating-point formatting toFixed, toExponential, toPrecision:
  • Math.sqrt(2).toPrecision(6) is '1.41421'

Constants

• Number constants MIN_VALUE, MAX_VALUE, MIN_SAFE_INTEGER, MAX_SAFE_INTEGER, EPSILON
  • Also NaN, POSITIVE_INFINITY, NEGATIVE_INFINITY
  • Same as global NaN, Infinity, -Infinity
• Math constants E, PI, SQRT2, SQRT1_2,LN2, LN10, LOG2E, LOG10E

Static Math Functions

Big Integers

• Arbitrary precision integers.
• Suffix n indicates big integer: 18446744073709551616n

  let n = 18446744073709551616n
  n * n // 340282366920938463463374607431768211456n

• Or create as BigInt(integer expression)
• Cannot mix BigInt with other numbers:

  let offset = 1
  n + offset // Error
  n + BigInt(offset) // Ok

• Just two static functions: BigInt.asIntN(bits, n) and BigInt.asUintN(bits, n) reduce modulo 2^bits into [-2^{bits - 1}...2^{bits - 1} - 1] or [0...2^bits - 1]

Dates

Constructing Dates

• Date measured in “milliseconds” (adjusted for leap seconds) since the “epoch” (midnight of January 1, 1970 UTC).
• Valid range ±100,000,000 days from epoch.
• new Date() yields current date/time.
• new Date(milliseconds) constructs Date from milliseconds.
  • new Date(10**12) // 2001-09-09T01:46:40.000Z
• Caution: Dates are converted to numbers in arithmetic expressions.

Constructing Calendar Dates

• Construct local calendar date/time: new Date(year, zeroBasedMonth, day, hours, minutes, seconds, milliseconds)
  • Everything starting from Day is optional.
  • const brendanEichsBirthday = new Date(1961, 6 /* July */, 4)
  • Caution: Out-of-range zeroBasedMonth, day, hours, etc. silently roll.
  • new Date(2019, 13, -2) // 2020-01-28
• For UTC, construct with date string in format YYYY-MM-DDTHH:mm:ss.sssZ (with literal T, Z):
  • const firstMillennialUTCnoon = new Date('2000-01-01T12:00:00.000Z')
  • Use ±YYYYYY for years outside 0000...9999
  • Caution: Other string formats may be accepted, but their format is not standardized.
• Caution: Date(...) without new constructs string (in non-standard format).

Static Date Functions

• Date.UTC(year, zeroBasedMonth, day, hours, minutes, seconds, milliseconds)
  • Everything after year optional.
• Date.parse(dateString)
  • Guaranteed support for YYYY-MM-DDTHH:mm:ss.sssZ format.
  • Other formats implementation-dependent.
• Date.now() is current date/time.
• All of these yield milliseconds, not Date object.

Getters and Setters

• Traditional getter/setter methods getHours/setHours, not get/set methods.
• Local time: getFullYear, getMonth (0-11), getDate (1-31), getHours (0-23), getMinutes, getSeconds, getMilliseconds
• Setters setFullYear, setMonth, and so on.
  • Setters silently roll: birthday.setMonth(13)
• getYear, setYear obsolete.
• UTC variants getUTCFullYear, getUTCMonth, and so on.
• Setters setUTCFullYear, setUTCMonth, and so on.

Date Formatting

• toIsoString yields string in YYYY-MM-DDTHH:mm:ss.sssZ format.
• toString, toDateString, toTimeString yield “humanly readable” string in local time zone, or only the date/time portion:

  'Tue Jul 09 2019 07:23:48 GMT+0200 (GMT+02:00)'
  'Tue Jul 09 2019'
  '07:23:48 GMT+0200 (GMT+02:00)'
  

• toUTCString yields “humanly readable” string in UTC:

  'Tue, 09 Jul 2019 05:23:48 GMT'

• toLocaleString, toLocaleDateString, toLocaleTimeString yield localized string:

  d.toLocaleTimeString('en-US') // '7:23:48 AM'
  d.toLocaleTimeString('de') // '07:23:48'
  

End of Lesson 5