JScript

See also: HTML

Debugging

To enable client-side debugging:

• Open IE
   
• Tools -> Internet Options -> Advanced
   
• Clear the "Disable Script Debugging" checkbox in the Browsing section

The debugger can be activated using the JScript equivalent of "int 3": debugger
    e.g. if i==0 debugger;

Normal break points (red dots introduced by clicking in the margin of the source code) do not appear to work (lasted checked: RC2)

Commenting

Standard C++ comment characters can be used within the <Script> block.

Datatypes

The datatype (or more correctly, to object from which the variable was constructed) is held in the constructor property. For example, if (myVar.constructor == String) alert("Its a string!").

Arrays

Arrays can store any type (and combination of types). The declaration syntax is:

• var myArray = new Array()
• var myArray = new Array(size)
• var myArray = new Array(element1, element2, ..., elementN)
• var myArray: Array = [element1, element2, ..., elementN]
• var i : int[] = new int[ size ];
• var i : int[,] = new int[ size, size ]

for example,
        var someDetails = new Array("Dave", 30, Date());

Although arrays can be declared with round brackets, they can only be accessed through square brackets, e.g. fred[2] = 10;

Dates

Constructors:

• var myVar = new Date()
  Constructs with current date-time
   
• var myVar = new Date(Year, Month, Day [, Hour, Minute, Seconds, ...]
  Constructs the date-time using the specified values

There is no "get friendly format" functions. For example, there is no "get month name from month number"

Not that the getMonth() function is 0 based, yet the constructor is 1 based.

Strings

Length:    Use the length property (no len(...) fn)

Case:       .toUpperCase() and .toLowerCase(). (no toProperCase())

Splice & Dice:

• .charCodeAt( [index] )
  ASCII code at position index or 0 if index not supplied
   
• .fromCharCode( index [, index [, ...]] )
  Returns a new string made up from the characters at the specified index positions in the source string
   
• .concat( string )
  "+=" equivalent (+= is also supported by the way)
   
• .indexOf( searchString [, startIndex] )
  .search( regularExpression )
  indexOf is quivalent to "AT()" equivalent except strings are 0 based and "no match" returns -1. search uses a regular expression instead of a literal string.
   
• .match( regularExpression )
  Returns an array if one or matches are found, else returns null.
   
• .replace( regularExpression, replacementString )
  Replaces all expressions that match regularExpression in the original string with replacementString
   
• .splice( [stringOrRegularExpression [, arraySizeLimit ]] )
  Returns an array from the string by using stringOrRegularExpression as a deliminator. If stringOrRegularExpression is not supplied an array of characters are returned. If its a single space, whitespace is "compressed" in the return (for example "space-space-tab" would be treated as a single break between values)
   
• .slice( startIndex [,endIndex] )
  .substr( startIndex [, length] )
  .substring( startIndex, endIndexPlusOne )
  .substring( endIndex, startIndexPlusOne )
  Returns the specified portion of the string
   

Encoding/decoding

• escape(string)
  unescape(string)
  Convert to and from "%" format (e.g. "Hello World" <--> "Hello%20World")

Other:

• HTML formating: .bold(), .italic(), etc.

Regular Expression Matching

• Regular expressions are bounded by the / character
   
• Expressions are implemented by storing the regular expression string to a variable and then calling methods on that variable or by using a regular expression as an argument in a string expression. Examples include:
   
  • regularExpressionVar.test(sourceString)
    Returns character index to the first match (or -1 if no match found)
     
  • string.search( regularExpression )
    string.replace( regularExpression, replacementString )
    see section of string for details 
     
• Single character matching

Code(s)		Meaning
\b	\B	Word boundary / not word boundary
\d	\D	Decimal (0-9) / not decimal
\s	\S	Single whitespace character / single non-whitespace character
\w	\W	Alphanumerical (i.e. not symbolic) or underscore / doesn't match \w
[xyz]	[^xyz]	Any of the characters represented in xyz / anything but the characters represented in xyz
.		Not newline / end of line?

For example: /\b[AB]C\b/
means: All occurrences of the words AB and AC

• Multiple character matching (modification characters)
  These codes modify the expression immediately to their left

Code	Meaning
*	Match expression zero or more times
?	Match expression zero or once
+	Match expression one or more times
{n}	Match expression exactly n times
{min,}	Match expression min or more times
{min, max}	Match expression between at least min times, but no more than max times

For example: /abc*de?/
means: All strings that begin with "ab" followed immediately by zero or more "c"s followed immediately by a "d" followed immediately by no more that one (possibly by zero) "e"s.

• Other modifiers

Code	Meaning
^	Match expression that follows with beginning of lines only
$	Match expression that follows with end of lines only
|	Match expression to the left or to the right (Note that this is a single "|" rather than JScripts normal "||"
(expression)	A bracketed expression will be included as an extra matching section in the results array

For example: /^Test/
matches: "Testing 1 2 3" but not "England have lost the 2nd Test"

For example: /(d)(d)(d)/ on "123"
returns an array of 3 elements {"1","2","3"} while /ddd/ (which we'd normally express as /d{3}/ returns an array of 1 element containing "123"

 

Switch Statements

Comparisons in switch statements are "= = =" rather than "= =", so types must match as well as values.

Case statements cannot contain multiple values (e.g. case 1,2,4:). If they do, they do not error but none of the values in the list are checked. Use "fall through" instead (e.g. case 1: case 2: case 4: <code> break;)

 

Events

• The Event object is global
   
• The state of the modifier keys can be checked by looking at:
  • Event.ALT_MASK
  • Event.CONTROL_MASK
  • Event.SHIFT_MASK
  • Event.META_MASK    (= Windows / Apple key)
     
• Events can be captured in two ways:
  • At the specific object:
    <span onClick="someJavaFunction([parameters]);">..
     
  • By specifying the events and handlers separately, for example:
    window.captureEvents(Event.KEYPRESS | Event.CLICK);
    window.onKeyPress = myKeyPressHandler;
    window.onClick = myClickHandler;
    (window.releaseEvents() to stop event capturing)
    ("document" is more often used than "window" because of frames and the ilk, but technically any object can be used)
     
• Useful events include
  • onBlur           Lost focus
  • onChange
  • onClick
  • onDblClick    Double Click
  • onError
  • onKeyDown, onKeyPress, onKeyUp
  • onLoad
  • onMouseDown, onMouseUp, onMouseOut, onMouseOver
  • onMove        (window object)
  • onReset        (form object)

Classes

• No true class structure
   
• Create a function that assigns values to attributes - effectively a constructor. Call that function with the new command and it will return an object even though the constructor function contains no return command and there is no class definition. For example:
   
  x = new myConstructor(1,2,3);
  ....
   
  function myConstructor(a,b,c) {
      this.xyz = a + b + c;
      this.anotherAttribute = "Hello World";
  }
   
• Methods can also be added in the constructor:
  
  function myConstructor(a,b,c) {
      ...
      this.myFunc = myFunc;
  }
   
  function myFunc(x,y) {
      this.z = x + y;
  }

Timers

• window.setInterval("funciton(...)", intervalInMilliseconds);
  Calls function(...) every intervalInMilliseconds
   
• window.setTimer("funciton()", intervalInMilliseconds);
  Calls function(...) once.

Document Handlers

• Events can be trapped at document level as well as at SCRIPT FOR and tag level, for example:
      document.onmousemove = myFunction;