CSC 107      Spring 2003

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. Variables are given values by using 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 the browser.

alert Anchor Area Array assign blur Boolean Button break Checkbox class clearTimeout close closed confirm continue Date defaultStatus delete document Document Element else escape eval false FileUpload focus for Form Frame frames function Function getClass Hidden History if Image in isNaN java JavaArray JavaClass JavaObject JavaPackage length Link Location location Math MimeType name navigate Navigator netscape new Number null Object onblur onerror onfocus onload onunload open opener Option Packages parent parseFloat parseInt Password Plugin prompt prototype Radio ref Reset return scroll Select self setTimeout status String submit sun taint Text Textarea this top toString true typeof unescape untaint valueOf void while window Window with




Operators:

Operator	Name	Data Types	Expressions	Values
+	Addition or Concatenation	Number String	3 + 1 4 + 7.432 "foo" + "bar"	4 11.432 "foobar"
-	Subtraction	Number	7 - 2 5 - 3.359	5 1.641
*	Multiplication	Number	2 * 5 10 * 9.773	10 97.73
/	Division	Number	10 / 4 2.5 / 8	2.5 0.3125
%	Remainder	Number	10 % 4 2 % 0.75	2 0.5
&&	AND	Boolean	true && true true && false false && true false && false	true false false false
||	OR	Boolean	true || true true || false false || true false || false	true true true false
!	NOT	Boolean	!true !false	false true




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 String*	2 < 3.1415 "a" < "b"
<=	Less Than or Equal	Number String*	17 <= 17 "ABC" <= "ABD"
>	Greater Than	Number String*	12 > -4 "foo" > "bar"
>=	Greater Than or Equal	Number String*	3.99 >= 3.98 "fool" >= "foo"
*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... /* Comment... */	// A one line comment. /* A comment that goes onto more than one line */
Assignment Statement	variable = expression; variable: sequence of letters, digits, and underscores that starts with a letter. expression: either a simple value (number, string, or boolean) or else operators applied to values. The value of the expression on the right-hand side is assigned to the variable on the left-hand side.	x = 7.5; FirstName = "Dave"; flag = true; prod2to4 = 2 * 3 * 4; // assigns value 24 y = (x + 1) * 3; // assigns value 25.5 hi_message = "Hello " + FirstName; // assigns value "Hello Dave" BOOL = true && !false; // assigns value true
If-Then Statement	if (test) { if-clause } else { else-clause } test: Evaluates to true or false. if-clause: Executed if test==true. else-clause: Executed if test==false. The else-clause is optional.	if (x >= 0) { x = x + 3; } if (x < 0) { x = x - 1; } else { x = x + 1; }
While Loop	while (test) { loop-body } test: Evaluates to true or false. loop body: Executed repeatedly, as long as test==true.	while (x >= 0) { x = x - 5; } int repCount = 0; while (repCount < 10) { document.write("Howdy<br>"); repCount = repCount + 1; }




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
Alert	alert("Welcome to my page."); The following alert box will appear.
Prompt	yourName = prompt("Please enter your name","Anonymous"); The following dialog box will appear, and yourName 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,...) { variable-declarations function-body return return-value; } 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" { return "foo"; } function BarFunc(N) // Assumes: N >= 0 // Returns: string of N "bar"s { var theStr; theStr = ""; while (N > 0) { theStr = theStr+"bar"; N = N - 1; } return theStr; } function Greet(name) // Assumes: name is a string // Results: displays greeting { document.write("Hi "+name); }
Function Call	myVar = FuncName(arg1, arg2,...); 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(); // Result: Str1 == "foo" Str2 = BarFunc(3); // Result: Str2 == "barbarbar" Greet("Dave"); // Result: displays "Hi Dave"