Notice: This material is excerpted from Special Edition Using JavaScript, ISBN: 0-7897-0789-6. The electronic version of this material has not been through the final proof reading stage that the book goes through before being published in printed form. Some errors may exist here that are corrected before the book is published. This material is provided "as is" without any warranty of any kind.

APPENDIX D - JavaScript Commands and Grammar

Finding information on programming in JavaScript can be a bit like looking for the Holy Grail. Between Netscape's site, online tutorials, and examples, information seems to be everywhere but at your fingertips. So here is the information you're looking for in one place, including statements, operators, and color values.

JavaScript Statements

The statements used to control program flow in JavaScript are similar to Java and C. A statement can span several lines if needed, or several statements can be placed on the same line. The important key to remember is that a semicolon must be placed between all statements. Since JavaScript is not strict in its formatting, you must provide the line breaks and indentation to make sure the code is readable and easy to understand later.

break

Terminates the current for or while loop and passes control to the first statement after the loop.

comment

Notes from the script author that are ignored by the interpreter. Single line comments are preceded by //. Multiple line comments begin with /* and end with */.

continue

Passes control to the condition in a while loop and to the update expression in a for loop.

for

Creates a loop with three optional expressions enclosed in parentheses and separated by semicolons, followed by a set of statements to be executed during the loop:

for( initialExpression; condition; updateExpression) {
statements...
}

The initial expression is used to initialize the counter variable, which can be a new variable declared with var. The condition expression is evaluated on each pass through the loop. If the condition is true, the loop statements are executed. The update expression is used to increment the counter variable.

for...in

Iterates a variable for all of properties of an object:

for (variable in object) {
statements...
}

For each property, it executes the statement block.

function

Declares a JavaScript function with a name and parameters. To return a value, the function must include a return statement. A function definition cannot be nested within another function.

function name ([parameter] [...,parameter]) {
statements...
}

if...else

A conditional statement that executes the first set of statements if the condition is true, and the statements following else if false. If...else statements can be nested to any level.

if (condition) {
statements...
} [else {
 statements...
}]

return

Specifies a value to be returned by a function.

return expression;

var

Declares a variable and optionally initializes it to a value. The scope of a variable is the current function or-when declared outside a function-the current document.

var variableName [=value] [..., variableName [=value]]

while

Repeats a loop while an expression is true.

while (condition) {
statements...
}

with

Establishes a default object for a set of statements. Any property references without an object are assumed to use the default object.

with (object) {
statements...
}

This statement is especially useful when applied to the Math object for a set of calculations. For example:

with (Math) {
var Value1 = cos(angle);
var Value2 = sin(angle);
}

replaces:

{
var Value1 = Math.cos(angle);
var Value2 = Math.sin(angle);
}

Operator Precedence

Precedence refers to the order in which compound operations are computed. Operators on the same level have equal precedence. Calculations are computed from left to right on all binary operations beginning with the operators at the top of the list and working down.

• call, member . [] ()
• negation/increment ++ - ! ~ -
• multiply/divide * / %
• addition/subtraction + -
• shift << >> >>>
• relational < > <= >=
• equality == !=
• bitwise AND &
• bitwise XOR ^
• bitwise OR |
• logical AND &&
• logical OR ||
• conditional ?:
• assignment = op=
• comma ,

JavaScript Objects

JavaScript is an object-oriented language, and as such, includes a set of built-in objects to represent the HTML document, especially form elements. Built-in objects can be accessed by both the client and server.

String

Contains a string of characters.

Math

Provides numerical constants and mathematical functions.

Date

Stores a date in the number of milliseconds since 1/1/1970, 00:00:00, and returns a date string in the format "Thu, 11 Jan 1996 06:20:00 GMT".

Document

The foundation object created with an HTML <BODY> tag and used to write other information to the page.

Form

An object for gathering and echoing data, created by HTML <FORM> tags.

Window

The highest precedence object accessible by JavaScript relating to the current open Navigator window. New windows and frames can also be created.

Reserved Words

The following words cannot be used as user objects or variables in coding JavaScript. Not all are currently in use by JavaScript-they are reserved for future use.

• abstract
• boolean
• break
• byte
• case
• catch
• char
• class
• const
• continue
• default
• do
• double
• else
• extends
• false
• final
• finally
• float
• for
• function
• goto
• if
• implements
• import
• in
• instanceof
• int
• interface
• long
• native
• new
• null
• package
• private
• protected
• public
• return
• short
• static
• super
• switch
• synchronized
• this
• throw
• throws
• transient
• true
• try
• var
• void
• while
• with

Color Values

Colors can be referenced in a variety of properties in two ways: by using the string literal or a RGB hexadecimal triplet formed by combining the three color values. For example, aliceblue is represented as F0F8FF.

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