CpSc 217 - Structured and Dynamic Web Programming

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This chapter is a partial Review from 130

Numbers

• Integers: 0, -5, 678
• Floating Point: 3.14, .3333, 6.02e23, 1.473E-32
• Arithmetic: +, -, *, /. %
• Math Object (see page 33 of text for complete list
  Math.round(.6)
  Math.random() //0 <= x < 1.0
  Math.pow(2,5)
  Math.floor(.6)
  Math.ceil(.6)
• Predefined Global Variables you should know
  Infinity
  
  Number.POSITIVE_INFINITY
  1/0
  Number.MAX_VALUE + 1
  
  Number.NEGATIVE_INFINITY
  -1/0
  -Number.MAX_VALUE - 1
  
  NaN
  Number.NaN
  0/0
• Floating point rounding errors
  Sample

  var x = .3 - .2; // 30 cents minus 20 cents
  var y = .2 - .1;  // 20 cents minus 10 cents
  x == y  // false !! not the same
  x == .1  // false !! not the same

Date Object

• var later = new Date(2013, 0, 1, 17, 10, 30); //Jan 1, 2013 5:10:30pm
  Sample
• Date Methods: later.getFullYear()
  later.getMonth() // 0
  later.getDate() // 1 first of month
  later.getDay() // 2; 0 for sunday, 1 for Monday,...
  later.getHours() // 17 which is 5pm

Strings

• null
• backslash is used to escape special characters
• single quotes or double quotes
• \n, \t
• String methods (page 38-39)
  s.length
  s.charAt(0)
  s.substring(1,4) // 2nd, 3rd, and 4th characters
  s.slice(1,4) // 2nd, 3rd, and 4th characters
  s.slice(-3) // last 3 charcters
  s.toUpperCase() // returns upper case - does not change string
  s.replace("e","E") // replaces all lowercase e with uppercase - does not change string
  s.indexOf("x") //index of where x is in the string
  s.split(",")
  Try it See page 254 for regular expression special characters


• Sample
• Pattern Matching - text between slashes interpreted as a regular expresion - /expression/
  ^ - starts with
  [0-9] range
  a* any number of a's
  \bword\b - match as a word
  \s - white space
  \S - not white space
  \d - digit
  \D - not a digit
  \w - any ASCII word character (letter, digit, number)
  a+ one or more a's

Booleans

• true false
• ==
• && ||

Global Objects

• global properties: undefined, Infinity, NaN
• global functions: parseInt(), eval(), isNaN()
• constructor functions: Date(), RegExp(), String(), Object(), Array()
• global objects: Math, JSON

Wrapper Objects

• Temporary objects created when you access a property of a string, number, or boolean

  var s = "test"  // a string value
  var S = new String(s)  // a string object
  var n = 1  // a number 
  var N = new Number(n)  // a number object
  var b = true  // a boolean value
  var B = new Boolean(b)  // a boolean object
  

Immuatable and Mutable Objects

• Immutable Object

  var s = "hello"
  s.toUpperCase() //returns uppercase, but doesn't change s
  

• Mutable Object

  var o = {x:1}; // object with single property
  o.x = 2; //change or mutate o by changing x
  o.y = 3; //mutate o by adding a property
  

• Arrays are also mutable
• Comparing objects:
  arrays - array a is not equal to array b unless set equal (a=b). They are reference types. To compare two arrays, use a loop
  Objects are also reference types. Have to write code to compare each property
• Try both

Type Conversions

• Will attempt to convert on the fly. See table 3-2 on page 46
• Explicit Conversions:

  Number("3") // returns 3
  String(false) // returns "false"
  Boolean([]) // returns true
  Object(3) // returns new Number(3)
  ({x:1, y:2}).toString() // returns "[object Object]"
  [1,2,3].toString()  // returns "1,2,3"
  

Variable Scope

• Global variable gl
• Local variable loc

  var gl = "global"
  funtion x() {
     var loc = "local"
  }