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NotesOnJavascriptTypes.md

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Data about JS Types for storage

Null

  • A value: null

Undefined

  • A value: undefined
    • Create safely with void 0

Boolean

  • Can be one of two values:
    • true
    • false

Object-Wrapped Boolean

  • Stores true or false as an Object wrapping a Boolean primitive
  • Can store arbitrary data on itself with String or Symbol keys

String

  • Stores text
  • All strings are immutable
  • Two instances of the same string share a reference to the same global string
  • Can hold unicode symbols without special conversions or encodings

Object-Wrapped String

  • Stores text as an Object wrapping a String primitive
  • Is represented internally as an array of characters
  • Can store arbitrary data on itself with String or Symbol keys

Number

  • A double-precision 64-bit binary format IEEE 754 value.
  • Can be decimal or integer, though all values are technically decimal
  • Can be positive or negative
  • Can represent numbers between -2^53 - 1 and 2^53 - 1
  • Has special number values:
    • -0
    • Infinity
    • -Infinity
    • NaN
  • Can also be specified with alternative literals, but these do not affect the value
    • binary (0b_)
    • octal (0_, 000_ and 0o_)
    • hexidecimal (0x_)

Object-Wrapped Number

  • Stores any Number as an Object wrapping a Number primitive
  • Can store arbitrary data on itself with String or Symbol keys

Regex

  • Regular pattern specified with slashes and optional flags afterward
  • Regex to data => [REGEX.source, REGEX.flags, REGEX.lastIndex]
  • Data representation to Regex => new Regex(DATA[0], DATA[1]), then, set the lastIndex value to DATA[2]
  • Can store arbitrary data on itself with String or Symbol keys

Date

  • Object containing date/time data
  • Date to Number => DATE.getTime()
  • Number to Date => new Date(TIME_NUMBER)
  • Note: If a Date was constructed with a value that cannot be converted into a date, the result is a Date Object with a value of "Invalid Date".
    • This can be detected by checking for NaN value when calling getTime()
    • Invalid Date objects created separately do not equal each other by default
    • This type of Date object can be encoded with an empty string
  • Can store arbitrary data on itself with String or Symbol keys

Object

  • key/value pairs
  • key can be a String or Symbol
  • value can be anything, including a reference to the parent object

Symbol

  • Globally unique value, usually
  • Can be used as an Object key
  • Creating Symbol by using Symbol() or Symbol(SOME_STRING) will always be unique, even if the SOME_STRING is used elsewhere
  • Symbol references can be duplicated, however, and will show being equal to themselves. var sym = new Symbol(); console.log(sym === sym); // true
  • Creating Symbol by using Symbol.for(SOME_STRING) will create a Registered Symbol with any other Symbol created with the same SOME_STRING using .for()
  • Passing a non-string to .for() will convert the value to a string using the String constructor
  • If the Symbol is Registered, calling Symbol.keyFor(SOME_SYMBOL) will result in the string key value for that Symbol
  • When creating a unique Symbol with a string Symbol('my string'), converting the Symbol to a string will retain the string value:
    • String(Symbol('my string')) // => Symbol(my string)
    • This includes empty string: String(Symbol('')) // => Symbol()
  • Symbols cannot accept arbitrary String or Symbol keys like some other Object-like types.
  • Cannot store arbitrary data on itself with String or Symbol keys

Array

  • A set of indexed values
  • Can store anything, including a reference to the array object
  • Can be a sparce array, so only store values at used indices
  • Optionally, non-integer String and Symbol keys can be attached to the Array, because it is built on Object.
  • Specifying integer keys as Strings will overwrite/create refer to the integer position in the Array, not the String key. That is, String keys of integers cannot be used with Arrays.
    • Even if specifying a key outside the range using an int converted to string will result in the creation of a sparce array with integer key.

Specified TypedArrays

  • Types
    • Int8Array
    • Uint8Array
    • Uint8ClampedArray
    • Int16Array
    • Uint16Array
    • Int32Array
    • Uint32Array
    • Float32Array
    • Float64Array
  • For the purposes of storage, acts very similarly to standard Arrays
  • Limited to storing numerical values in the indexed fields
  • Cannot be expanded beyond the defined bounds
  • Cannot be sparse -- by default, the unset values are initialized to 0
  • Can store other data via String or Symbol keys

ArrayBuffer

TODO

SharedArrayBuffer

TODO

Set

TODO

Map

TODO

Blob

TODO

File

TODO

BigInt

TODO