MCS 170 - Spring 2005

---

Data Types:

Data Type	Examples
Number	1 1024 18.0 3.14159 1.024e3
String	"" "foo" "2 words"
Boolean	true false

Variables:

A variable is a symbolic name for an unspecified value in an expression or statement. A variable can be used in any situation where the data that it refers to can be used. A variable name can refer to any of the data types, described above. Variables are given values by using the "=" symbol (the assignment operator)  as described below. All of the examples below make use of variables (e.g. x, y, Str, flag, etc...)

The following lists identify variable names that should be avoided because they are already used by JavaScript or Netscape.

JavaScript Reserved Words break continue delete else <br> false for function if<br> in new null return<br> this true typeof var<br> void while with<br> Java Keywords Reserved by JavaScript abstract boolean byte case<br> char class const default<br> do double export extends<br> final finally float goto<br> implements import instanceof int<br> interface long native package<br> private protected public short<br> static super switch synchronized<br> throw throws transient try<br> Other Variable Names to Avoid alert Anchor Area arguments<br> Array assign blur Boolean<br> Button callee caller CaptureEvents<br> Checkbox clearInterval clearTimeout close<br> closed confirm constructor Date<br> defaultStatus Document document Element<br> escape eval FileUpload find<br> focus Form Frame frames Function getClass Hidden History<br> history Image Infinity innerHeight<br> innerWidth isFinite isNaN java<br> JavaArray JavaClass JavaObject JavaPackage<br> length Link Location location<br> locationbar Math menubar MimeType<br> moveBy moveTo name NaN<br> navigate Navigator netscape Number<br> Object onblur onerror onfocus<br> onload onunload open opener<br> Option outerHeight outerWidth Packages<br> pageXOffset pageYOffset parent parseFloat parseInt Password personalbar<br> Plugin<br> print prompt prototype Radio ref RegExp releaseEvents Reset<br> resizeBy resizeTo routeEvent scroll scrollBars scrollBy scrollTo Select<br> self setInterval setTimeout status statusbar stop String Submit<br> sun taint Text Textarea<br> toolbar top toString unescape<br> untaint unwatch valueOf watch Window window<br>
Source: JavaScript the Definitive Guide. David Flanagan, O'Reilly & Associates, Inc. 1998.

Operators:

Operator	Name	Data Types	Examples	Result
=	Assignment	Number String Boolean	x = 3; y = 7.654; Str = "foo"; flag = true;	x == 3 y == 7.654 Str == "foo" flag == true
+	Addition or Concatenation	Number String	x = 4 + 3; y = x + 7.432; Str = "foo" + "bar";	x == 7 y == 14.432 Str == "foobar"
-	Subtraction	Number	x = 7 - 2; y = x - 3.359;	w == 5 y == 1.641
*	Multiplication	Number	x = 2 * 5; y = x * 9.773;	x == 10 y == 97.73
/	Division	Number	x = 10 / 4; y = x / 8;	x == 2.5 y == .3125
%	Remainder1	Number	x = 10 % 4; y = x % .75;	x == 2 y == .5
&&	AND	Boolean	flag = true; D = true && flag; D = D && false;	flag == true D == true D == false
||	OR	Boolean	flag = true; D = flag || true; D = false || D;	flag == true D == true D == false
!	NOT	Boolean	D = !true; D = !D;	D == false D == true
1. The Remainder operator is often referred to as the Modulo operator.

Comparison:

Operator	Name	Data Types	Examples
==	Equality	Number String Boolean	3 == 3 "test" == "test" false == false
!=	Inequality	Number String Boolean	12 != 39 "foo" != "bar" false != true
<	Less Than	Number String1	2 < 3.1415 "a" < "b"
<=	Less Than or Equal	Number String1	17 <= 17 "ABC" <= "ABD"
>	Greater Than	Number String1	12 > -4 "foo" > "bar"
>=	Greater Than or Equal	Number String1	3.99 >= 3.98 "fool" >= "foo"
1. Strings follow standard dictionary ordering, i.e.,     "A" < "B" < ... < "Z" < "a" < "b" ... < "z"     "a" < "aa" < ... < "ab" < "aba" < ... < "b"

Statements:

Statement Name	General Form	Examples
Comment	// Comment...<br> /* Comment... */<br>	// A one line comment.<br> /* A comment that goes onto more than one line */<br>
If-Then Statement	if (test) { if-clause<br> } else { else-clause<br> }<br> test: Evaluates to true or false. if-clause: Executed if test==true. else-clause: Execued if test==false. The else-clause is optional.	// add 3 to x if non-neg.<br> if (x &amp;gt;= 0) { x = x + 3;<br> }<br> // decrement x if neg.,<br> // otherwise increment<br> if (x &amp;lt; 0) { x = x - 1;<br> }<br> else { x = x + 1;<br> }<br>
While Loop	while (test) { loop-body<br> }<br> test: Evaluates to true or false. If test==true the loop body is executed and the test is performed again.	// sum = x+(x-1)+...+3+2+1<br> sum = 0;<br> while (x &amp;gt;= 1) { sum = sum + x; x = x - 1;<br> }<br>
For Loop	for (init; test; action) { loop-body<br> }<br> init: Evaluated once when the for loop is first reached. test: If test==true the loop body will execute. action: Executed after the loop body and before the next evaluation of test.	// sum = 1+2+3+...+x<br> sum = 0;<br> for (i = 1; i &amp;lt;= x; i = i + 1) { sum = sum + i;<br> }<br> // fact = 1*2*3*...*10<br> fact = 1;<br> for (j = 2; j &amp;lt;= 10; j = j + 1) { fact = fact * j;<br> }<br>

Built In Functions:

Function	Examples	Result
Square Root	x = Math.sqrt(9);	x == 3
Absolute Value	x = Math.abs(-23); y = Math.abs(99);	x == 23 y == 99
Maximum	x = Math.max(3,14);	x == 14
Minimum	x = Math.min(3,14);	x == 3
Power	x = Math.pow(2,3);	x == 8
Floor	x = Math.floor(3.14159); y = Math.floor(4.5623);	x == 3 y == 4
Ceiling	x = Math.ceil(3.14159); y = Math.ceil(4.5623);	x == 4 y == 5
Round	x = Math.round(3.14159); y = Math.round(4.5623);	x == 3 y == 5
ParseFloat	x = parseFloat("12.8"); y = parseFloat("ABC");	x == 12.8 y == NaN
Prompt	theName = prompt("Enter Your Name:","Default Value"); Netscape will display a dialog box, and theName will be assigned the value that is entered in the text field.
Write	document.write("Howdy"); document.write(2+3);	displays "Howdy" displays 5

User Defined Functions

Action	General Form	Examples
Function Definition	function FuncName(param1, param2,...) {<br> variable-declarations function-body return return-value;<br> }<br> FuncName: The name of the function. param1: The name of the first parameter passed to the function. variable-declarations: list of local variables (if any) that appear in the function, preceded by var. function-body: JavaScript statements to be executed when the function is called. return-value: Value that is returned from this function. The return statement is optional.	function FooFunc() // Returns: the string "foo"<br> { return "foo";<br> }<br> function BarFunc(N)<br> // Assumes: N &amp;gt;= 0<br> // Returns: string of N "bar"s<br> { var i, theStr; theStr = ""; for (i = 1; i &amp;lt;= N; i = i + 1) {<br> theStr = theStr+"bar"; } return theStr;<br> }<br> function Greet(name)<br> // Assumes: name is a string<br> // Results: displays greeting<br> { document.write("Hi "+name);<br> }<br>
Function Call	myVar = FuncName(arg1, arg2,...);<br> myVar: Variable to hold the value (if any) returned by the function. FuncName: Name of the function to call. arg1: Argument 1, the value for the first parameter of the function.	Str1 = FooFunc();<br> // Result: Str1 == "foo" Str2 = BarFunc(3);<br> // Result: Str2 == "barbarbar"<br> Greet("Dave");<br> // Result: displays "Hi Dave"<br>