ES6

The Primitives

Goal

• Review ECMAScript Version 6 extensions and changes to the primitive values, with:
  • Support in current environments
  • Function types
  • Simple code examples

Number

• Octal Literals

  Base 8 number literal syntax

  0o10 === 8 && 0O10 === 8

• Binary Literals

  Base 2 number literal syntax

  0b10 === 2 && 0B10 === 2

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.isFinite
  Number -> Boolean

  Returns false for Infinity and NaN, true otherwise

  Number.isFinite(Infinity)  === false

  Number.isFinite(-Infinity) === false

  Number.isFinite(NaN)       === false

  Number.isFinite(1)         === true

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.isInteger
  Number -> Boolean

  Returns true if the input is an integer, false otherwise.

  Number.isInteger(Infinity)  === false

  Number.isInteger(-Infinity) === false

  Number.isInteger(NaN)       === false

  Number.isInteger(1.1)       === false

  Number.isInteger(1)         === true

  Number.isInteger(0)         === true

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.isSafeInteger
  Number -> Boolean

  Returns true for integers between -253 and 253, false for other values.

  Number.isSafeInteger(-Math.pow(2, 53))     === false

  Number.isSafeInteger(-Math.pow(2, 53) + 1) === true

  Number.isSafeInteger(Math.pow(2, 53))      === false

  Number.isSafeInteger(Math.pow(2, 53) - 1)  === true

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.isNaN
  a -> Boolean

  Returns true for NaN, false otherwise.

  Number.isNaN(NaN) === true

  Number.isNaN(0)   === false

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.EPSILON

  The value 2-52. Very loosely, the smallest difference that can be represented as a Number.

  Number.EPSILON  === Math.pow(2, -52) === 2.220446049250313e-16

  0.1 + 0.2       !== 0.3

  0.1 + 0.2 - 0.3 === 5.551115123125783e-17

  0.1 + 0.2 - 0.3 <   Number.EPSILON

• Full
• Beta
• Flag
• None
• Non-Standard

Number

• Number.MIN_SAFE_INTEGER

  The number -253-1 or -9007199254740991

• Number.MAX_SAFE_INTEGER

  The number 253-1 or 9007199254740991

• Full
• Beta
• Flag
• None
• Non-Standard

String

• Template Strings

  A new type of string literal allowing:

  • Value interpolation
  • Multi-line strings
  • String processing functions (tagged template strings)

  var name = 'bob';
  `my name is ${name}` === 'my name is bob'

  `Here is a 
  Multi-line 
  string`

• Full
• Beta
• Flag
• None
• Non-Standard

String

• Unicode code point escapes

  Allows all Unicode characters to be represented by a single code point value.

  '\u{1D306}' === '\uD834\uDF06'

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.fromCodePoint
  ...[Number] -> String

  Returns a string composed of the code point arguments.

  String.fromCodePoint(55, 78) === '7N'

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.raw
  [String], ...[*] -> String

  A built in template string tag. Returns a string with all escape sequences rendered literally.

  String.raw`A\nB` !== 'A\nB'

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.codePointAt
  @String, Number -> Number

  Returns the UTF-16 encoded code point value at the given index of the receiving string.

  String.fromCodePoint('01234'.codePointAt(3)) === '3'

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.normalize
  @String, String -> String

  Returns the "Unicode Normalization Form" of the receiving string, according to the specified form.

  '\u1E9B\u0323'.normalize('NFKC') !== '\u1E9B\u0323'.normalize('NFD')

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.repeat
  @String, Number -> String

  Returns a new string formed by concatenating the receiving string with it self the specified number of times.

  'abc'.repeat(4) === 'abcabcabcabc'

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.startsWith
  @String, String -> Boolean

  Returns true if the receiving string begins with the passed string, false otherwise.

  'abcdefg'.startsWith('abc')  === true

  ' abcdefg'.startsWith('abc') === false

  'abcdefg'.startsWith('')     === true

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.endsWith
  @String, String -> Boolean

  Returns true if the receiving string ends with the passed string, false otherwise.

  'abcdefg'.endsWith('efg')  === true

  'abcdefg '.endsWith('efg') === false

  'abcdefg'.endsWith('')     === true

• Full
• Beta
• Flag
• None
• Non-Standard

String

• String.prototype.includes
  @String, String, Number -> Boolean

  Returns true if the receiving string has a substring matching the passed string, beginning at the passed index; false otherwise.

  'abcdefg'.includes('efg')    === true

  'abcdefg'.includes('abc', 4) === false

  'abcdefg'.includes('')       === true

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol
  String -> Symbol

  Returns a new Symbol with the passed string label. The label is not unique.

  Symbol('abc') !== Symbol('abc')

  var prop  = Symbol(),
      obj   = {};
  obj[prop] = 'My value';
  
  obj[prop]     === 'My value'
  obj[Symbol()] === undefined

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol.for
  String -> Symbol

  Returns the shared symbol from the global symbol registry for the provided string.

  Symbol.for('abc') === Symbol.for('abc')

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol.keyFor
  Symbol -> String

  Returns the string key for the passed symbol in the global symbol registry.

  Symbol.keyFor(Symbol.for('abc')) === 'abc'

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol.hasInstance

  Customizes instanceof operator.

• Symbol.isConcatSpreadable

  Customizes Array.prototype.concat.

• Symbol.iterator

  Customizes for...of loops.

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol.species

  Reference to an object's constructor function.

• Symbol.toPrimitive

  Customizes internal ToPrimitive operation.

• Symbol.toStringTag

  Customizes object's stringification.

• Full
• Beta
• Flag
• None
• Non-Standard

Symbol

• Symbol.unscopables

  Customizes with operator.

• Full
• Beta
• Flag
• None
• Non-Standard