JavaScript Reference Card [Goelz & Schwartz 2004-09-10].pdf

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Addison-Wesley’s
JavaScript Reference Card
Kathleen M. Goelz and Carol J. Schwartz, Rutgers University
Javascript : A scripting language designed to be integrated
into HTML code to produce enhanced, dynamic, interac-
tive web pages.
VARIABLES
Definition : A placeholder for storing data. In JavaScript, a
declaration statement consists of the reserved word var and
the name (identifier) of one or more variables.
Format :
var variable_name
[ var command is used to declare (create) variables]
Examples :
var myHouseColor
var myAddress
var vacation_house, condominium,
primaryResidence
Rules for Naming Variables :
1. Variables cannot be reserved words.
2. Variables must begin with a letter or underscore and
cannot begin with symbols, numbers, or arithmetic
notations.
3. Spaces cannot be included in a variable name.
Hints :
1. Although variables in JavaScript can be used without
being declared, it is good programming practice to
declare (initialize), all variables.
2. Variable names are case sensitive; for example X does
not equal x.
DATA TYPES
Definition : The classification of values based on the specific
categories in which they are stored.
Primitive Types : String, Boolean, Integer, Floating Point,
Null, Void
Composite Types: Object, Array, Function. Composite data
types are in separate sections of the code.
NUMERIC
Integer: Positive or negative numbers with no fractional
parts or decimal places.
Floating Point : Positive or negative numbers that contain a
decimal point or exponential notations.
String : A sequence of readable characters or text, surround-
ed by single or double quotes.
Boolean : The logical values True/False, etc. used to com-
pare data or make decisions.
Null: The variable does not have a value; nothing to report.
Null is not the same as zero, which is a numeric value.
Casting : Moving the contents of a variable of one type to a
variable of a different type. You don’t move the contents to
a different variable; it stays in the same variable but the
data type is changed or “re-cast”.
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ISBN 0-321-32075-1
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INITIALIZING VARIABLES
Use the declaration statement to assign a value to the vari-
able. The value is on the right of the equal sign; the variable
is on the left.
Format :
var variable_name = value
Examples :
var myHouseColor = “yellow”
[literal string value yellow assigned to variable
myHouseColor ]
var myAddress = 473
[numeric value 473 assigned to variable myAddress ]
var bookTitle = “Time Capsule”, cost =
28.95, publisher = “Tucker Bay”
[multiple variables can be assigned in one statement]
IF-ELSE Statement: A conditional branching statement
that includes a path to follow if the condition is TRUE and
a path to follow if the condition is FALSE.
Format :
if (condition) {
statements if condition is TRUE;
}
else {
statements if condition is FALSE;
}
Example :
if (score >= 65) {
grade = “Pass”;
message = “Congratulations”;
}
else {
grade = “Fail”
message = “Try again”;
DECISION MAKING AND
CONTROL STRUCTURES
}
IF-ELSE IF Statement: A conditional branching statement
that allows for more than two possible paths. The first time
a true condition is encountered, the statement is executed
and the remaining conditions will not be tested.
Format:
if (condition) {
Statements if condition is TRUE;
Definition : Statements and structures used to change the
order in which computer operations will occur.
Types :
Conditional Branching IF, IF-ELSE, IF-ELSE IF, SWITCH,
WHILE, DO, FOR
CONDITIONALS
IF Statement: A conditional branching statement used to
determine whether a stated condition is TRUE.
Format :
if (condition) {
statements if condition is TRUE
}
else if (condition) {
Statements if condition is TRUE;
}
else {
Statements if no prior condition is
true;
}
Example :
if (score >= 65”) {
grade = “Pass”;
message = “Congratulations”;
}
}
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Example:
if
(score>=90) {
grade=”A”;
Example:
switch (colorchoice) {
case “red”:
document.bgColor=”red”;
break;
case “blue”:
document.bgColor=”blue”;
break;
default:
document.bgColor=”white”;
break;
}
else if (score>=80) {
grade=”B”;
}
else if (score>=70) {
grade=”C”;
}
else if (score>=65) {
grade=”D”;
}
}
else
{
LOOPS
Loops cause a segment of code to repeat until a stated
condition is met. You can use any loop format for any
type of code
grade=”F”;
}
SWITCH Statement: An alternative to the IF-ELSE IF
statement for handling multiple options. Compares the
expression to the test values to find a match.
Format:
switch (expression or variable name) {
case label:
statements if expression matches
this label;
break;
case label:
statements if expression matches
this label;
break;
default:
statements if expression does not
match any label;
break;
FOR LOOP :
Format:
For (intialize; conditional test;
increment/decrement) {
Statements to execute;
}
Example:
For (var i=0; i<=10; i++) {
document.write (“This is line “ + i);
}
DO/WHILE LOOP :
Format:
do {
Statements to execute;
}
while (condition);
Example:
var i=0;
do {
document.write (“This is line “ + i);
i++;
}
}
while (i <=10);
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WHILE LOOP:
Format:
while (condition) {
Statements;
Increment/decrement;
Initializing Arrays :
Array items can be treated as simple variables:
days[0] = “Sunday”;
days[1] = “Monday”;
etc.
}
Example:
var i = 0;
while (i<=10) {
document.write (“This is line “ + i);
i++;
STRING OBJECT
Definition: String object is created by assigning a string to a
variable, or by using the new object constructor.
Example:
var name = “Carol”;
var name = new String(“Carol”);
Properties:
Length: returns the number of characters in the
string
Prototype: allows the user to add methods and
properties to the string
}
Hint: Watch out for infinite loops, which do not have a
stopping condition or have a stopping condition that will
never be reached.
OBJECTS
Definition: Objects are a composite data type which con-
tain properties and methods. JavaScript contains built-in
objects and allows the user to create custom objects.
Creating Objects: Use the new constructor
var X = new Array()
Examples:
date, time, math, strings, arrays
Methods:
String formatting methods (similar to HTML formatting tags)
String.big
String.blink
String.italics
Substring methods (allow user to find, match, or change
patterns of characters in the string)
indexOf()
charAt()
replace()
ARRAY OBJECT
Definition: Array object is a variable that stores multiple val-
ues. Each value is given an index number in the array and
each value is referred to by the array name and the
index number. Arrays, like simple variables, can hold any
kind of data. You can leave the size blank when you create
an array. The size of the array will be determined by the
number of items placed in it.
Format:
var arrayname = new Array(size)
Hint: When you create an array, you create a new instance
of the array object. All properties and methods of the array
object are available to your new array.
Example:
var days = new Array (7)
This creates an array of seven elements using the array
constructor.
The first item is days[0] , the last item is days[6] .
MATH OBJECT
Definition: Math object allows arithmetic calculations not
supported by the basic math operators. Math is a built-in
object that the user does not need to define.
Examples:
Math.abs(number) returns absolute value of
the numeric argument
Math.cos(number) returns the cosine of the
argument, in radians
Math.round(number) rounds number to the
nearest integer
DATE/TIME OBJECTS
Date object provides methods for getting or setting infor-
mation about the date and time.
Note: Dates before January 1, 1970 are not supported.
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FUNCTIONS
PUTTING IT TOGETHER:
JAVASCRIPT AND HTML
ON THE WEB
Definition: A pre-written block of code that performs a
specific task. Some functions return values; others perform
a task like sorting, but return no value. Function names
follow the same rules as variables names. There may or
may not be an argument or parameter in the parenthesis,
but the parenthesis has to be there.
User-defined Functions:
Example:
ParseInt() or ParseFloat() convert a string to a
number.
To create a function:
Format:
function name_of_function (arguments) {
statements to execute when
function is called;
Cookies : Text-file messages stored by the browser on the
user’s computer
Purpose : To identify the user, store preferences, and present
customized information each time the user visits the page
Types :
Temporary (transient, session) — stored in temporary
memory and available only during active browser session
Persistent (permanent, stored) — remain on user’s comput-
er until deleted or expired
Browser Detection : A script written to determine which
browser is running; determine if the browser has the capabili-
ties to load the webpage and support the javascript code; and,
if needed, load alternate javascript code to match the browser
and platform.
}
Example:
function kilosToPounds (){
pounds=kilos*2.2046;
Sniffing : A script written to determine whether a specific
browser feature is present; i.e., detecting the presence of
Flash before loading a webpage.
}
This new function takes the value of the variable kilos,
multiplies it by 2.2046, and assigns the result to the vari-
able pounds.
To call a function: Give the name of the function followed
by its arguments, if any
ParseInt(X); converts the data stored in the variable
X into a numeric value.
kilosToPounds(17); converts 17 kilos to the same
mass in pounds, returning the value 37.4782.
Event Handling: Use HTML event attributes (mouseover,
mouse click, etc.) and connect event to a JavaScript function
called an event handler
METHODS
Definition : A special kind of function used to describe or
instruct the way the object behaves. Each object type in
JavaScript has associated methods available.
Examples :
array.sort();
document.write();
string.length();
Calling: To call or use a method, state the method name
followed by its parameters in parentheses.
Example:
document.write(“Hello, world!”);
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