Syntax

Values

-Most of JavaScript’s data is separated in to things called values.
-There are six basic types of values.

• Numbers
  • Only one number type (no integers)
  • 64-bit floating point
  • Does not map well to common understanding of arithmetic
  • NaN
    • Not a number
    • NaN = Nan = False
    • NaN not > NaN or < NaN
  • Number Function
    • Number(value)
    • convert a value such as string to a number if string cant be converted return NaN
  • ParseInt Function
    • ParseInt(value,10)
    • Converts the value into a number
    • The radix argument should be required as it tells what base to calculate
  • JS has a Separate Math Object (modeled on Java’s Math Class)
    • floor *most useful
    • abs
    • log
    • max
    • pow
    • random
    • round
    • sin
    • sqrt
    • absolute value
    • integer
    • logarithm
    • maximum
    • raise to a power
    • random number
    • nearest integer
    • sine
    • square root

• Strings
  • Sequence of 0 or more 16-bit Characters (ucs-2 not quite UTF-16: Created before unicode have matured)
  • No Separate Character Type
  • Characters are represented as strings with a length of 1
  • Strings are immutable > once a string is made it can’t be modified
  • Similar strings are equal (==)
  • String literals can use single or double quotes
  • String Length
    • string.length
    • determines the number of 16-bit characters in a string
  • String Function
    • String(value)
    • converts value to a string (number function can do too, slightly more graceful)
  • String Methods
    • charAt
    • concat
    • indexOf
    • lastIndexOf
    • match
    • replace
    • search
    • slice
    • split
    • subString
    • toLowerCase
    • toUpperCase

• Booleans
  • True
  • False
  • Boolean Function
    • boolean(value)
    • returns true if value is truthy
    • returns false if value is falsy
    • similar to !! prefix operator
• Undefined
  • a value that isn’t even that
  • the default value for variables and parameters
  • the value of missing members in objects
  • Falsy Values
    • false
    • null
    • undefined
    • ” ” empty string
    • 0
    • NaN
    • All other values (including all objects) are truthy (beware of “0” and “false” these are often confused for false
• Null
  • a value that isn’t anything
• Objects (everything else)
  • Unification of Object and Hashtable
    • newObject()
    • produces and empty container of name/value pairs
      • a name can be any string, a value can be any value except undefined

JavaScript is Syntactically a C Family Language

-It differs from C mainly in its type system which allows functions to be values
Identifiers

• Starts with a letter or _ or $
• Followed by zero or more letters, digits, _ or $
• Case Sensitibbe
• by convention, all bariables, parameters, membersm and function names start with lower case
• except for constructors which start with upper case
• intitial _ should be reserved for implementations
• @ should be reserved for machines (better to avoid)

Reserved Words

• abstract
• boolean break byte
• case catch char class const continue
• debugger default delete do double
• else enum export extends
• false final finally float for function
• goto
• if implements import in instanceof int interfence
• long
• native new null
• package private protected public
• return
• short static super switch synchronized
• this throw throws transient true try typeof
• var volatile void
• while with

Comments

• // line comment
• /* block comment */

Operators

• Arithmetic: + – * / %
• Comparison: == !- <> <= >=
• Logical: && || !
• Bitwise: $ | ^ >> >>> <<
• Ternary: ?:

Sourced from (http://www.diycomputerscience.com/courses/course/JAVASCRIPT/competency/185) Douglas Crockford