Java Script Quick Reference

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

assignment operator

x

y

Str

flag

JavaScript Reserved Words

break continue delete else false for function if in new null return this true typeof var void while with

Java Keywords Reserved by JavaScript

absract boolean byte case char class const default do double extends final finally float goto implements import instanceof int interface long native package private protected public short static super switch synchronized throw throws transient try

Other Variable Names to Avoid

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

Source: JavaScript the Definitive Guide. David Flanagan, O'Reilly & Associates, Inc. 1997.

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	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`
++	Increment	Number	`x++;`	`x = x + 1`
--	Decrement	Number	`y--;`	`y = y - 1`
&&	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 also called the Modulus 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
For Loop	`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.
If-Then Statement	`test`: Evaluates to `true` or `false`. `if-clause`: Executed if `test==true`. `else-clause`: Execued if `test==false`. The else-clause is optional.
While Loop	`test`: Evaluates to `true` or `false`. If `test==true` the loop body is executed and the test is performed again.

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`
Parse Float	`x = parseFloat("12.8"); y = parseFloat("ABC");`	`x == 12.8 y == NaN`
Prompt	`theName = prompt("Enter Your Name:","Default Value");` Netscape will display the following 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	`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 Call	`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.