Java script

http://www.codeproject.com/KB/scripting/jsbeginner.aspx

Are Java and JavaScript the Same?

NO!

Java and JavaScript are two completely different languages in both concept and design!

Java (developed by Sun Micro systems) is a powerful and much more complex programming language - in the same category as C and C++.
What can a JavaScript Do?

* JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages
* JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("

" + name + "

") can write a variable text into an HTML page
* JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element
* JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element
* JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing
* JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser
* JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer

How to Put a JavaScript Into an HTML Page







HTML Comments to Handle Simple Browsers

Browsers that do not support JavaScript will display JavaScript as page content.

To prevent them from doing this, and as a part of the JavaScript standard, the HTML comment tag can be used to "hide" the JavaScript. Just add an HTML comment tag (end of comment) after the last JavaScript statement.








Where to Put the JavaScript

JavaScripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.

Scripts in the head section: Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it.






Scripts in the body section: Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page.








Scripts in both the body and the head section: You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.










Using an External JavaScript

Sometimes you might want to run the same JavaScript on several pages, without having to write the same script on every page.

To simplify this, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension.

Note: The external script cannot contain the





JavaScript is Case Sensitive

JavaScript Code

JavaScript code (or just JavaScript) is a sequence of JavaScript statements.

Each statement is executed by the browser in the sequence they are written.

This example will write a header and two paragraphs to a web page:



JavaScript Blocks

JavaScript statements can be grouped together in blocks.

Blocks start with a left curly bracket {, and ends with a right curly bracket }.

The purpose of a block is to make the sequence of statements execute together.

This example will write a header and two paragraphs to a web page:



JavaScript Comments

Comments can be added to explain the JavaScript, or to make it more readable.

Single line comments start with //.

This example uses single line comments to explain the code:



JavaScript Multi-Line Comments

Multi line comments start with /* and end with */.

This example uses a multi line comment to explain the code:



Using Comments at the End of a Line

In this example the comment is placed at the end of a line:



JavaScript Variables

As with algebra, JavaScript variables are used to hold values or expressions.

A variable can have a short name, like x, or a more descriptive name like carname.

Rules for JavaScript variable names:

* Variable names are case sensitive (y and Y are two different variables)
* Variable names must begin with a letter or the underscore character

NOTE: Because JavaScript is case-sensitive, variable names are case-sensitive.
Example

A variable's value can change during the execution of a script. You can refer to a variable by its name to display or change its value.

This example will show you how
Declaring (Creating) JavaScript Variables

Creating variables in JavaScript is most often referred to as "declaring" variables.

You can declare JavaScript variables with the var statement:

var x;
var carname;

After the declaration shown above, the variables have no values, but you can assign values to the variables while you declare them:

var x=5;
var carname="Volvo";

Note: When you assign a text value to a variable, you use quotes around the value.
Assigning Values to JavaScript Variables

You assign values to JavaScript variables with assignment statements:

x=5;
carname="Volvo";

The variable name is on the left side of the = sign, and the value you want to assign to the variable is on the right.

After the execution of the statements above, the variable x will hold the value 5, and carname will hold the value Volvo.
Assigning Values to Undeclared JavaScript Variables

If you assign values to variables that have not yet been declared, the variables will automatically be declared.

These statements:

x=5;
carname="Volvo";

have the same effect as:

var x=5;
var carname="Volvo";


Redeclaring JavaScript Variables

If you redeclare a JavaScript variable, it will not lose its original value.

var x=5;
var x;

After the execution of the statements above, the variable x will still have the value of 5. The value of x is not reset (or cleared) when you redeclare it.
JavaScript Arithmetic

As with algebra, you can do arithmetic with JavaScript variables:

y=x-5;
z=y+5;

You will learn more about the operators that can be used between JavaScript variables in the next chapter of this tutorial.


The operator = is used to assign values.

The operator + is used to add values.

The assignment operator = is used to assign values to JavaScript variables.

The arithmetic operator + is used to add values together.

y=5;
z=2;
x=y+z;

The value of x, after the execution of the statements above is 7.
JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic between variables and/or values.

Given that y=5, the table below explains the arithmetic operators:
Operator Description Example Result
+ Addition x=y+2 x=7
- Subtraction x=y-2 x=3
* Multiplication x=y*2 x=10
/ Division x=y/2 x=2.5
% Modulus (division remainder) x=y%2 x=1
++ Increment x=++y x=6
-- Decrement x=--y x=4

JavaScript Assignment Operators

Assignment operators are used to assign values to JavaScript variables.

Given that x=10 and y=5, the table below explains the assignment operators:
Operator Example Same As Result
= x=y x=5
+= x+=y x=x+y x=15
-= x-=y x=x-y x=5
*= x*=y x=x*y x=50
/= x/=y x=x/y x=2
%= x%=y x=x%y x=0

The + Operator Used on Strings

The + operator can also be used to add string variables or text values together.

To add two or more string variables together, use the + operator.

txt1="What a very";
txt2="nice day";
txt3=txt1+txt2;

After the execution of the statements above, the variable txt3 contains "What a verynice day".

To add a space between the two strings, insert a space into one of the strings:

txt1="What a very ";
txt2="nice day";
txt3=txt1+txt2;

or insert a space into the expression:

txt1="What a very";
txt2="nice day";
txt3=txt1+" "+txt2;

After the execution of the statements above, the variable txt3 contains:

"What a very nice day"
Adding Strings and Numbers

Look at these examples:

x=5+5;
document.write(x);

x="5"+"5";
document.write(x);

x=5+"5";
document.write(x);

x="5"+5;
document.write(x);



Comparison Operators

Comparison operators are used in logical statements to determine equality or difference between variables or values.

Given that x=5, the table below explains the comparison operators:
Operator Description Example
== is equal to x==8 is false
=== is exactly equal to (value and type) x===5 is true
x==="5" is false
!= is not equal x!=8 is true
> is greater than x>8 is false
< is less than x<8 is true >= is greater than or equal to x>=8 is false
<= is less than or equal to x<=8 is true How Can it be Used Comparison operators can be used in conditional statements to compare values and take action depending on the result: if (age<18) document.write("Too young"); You will learn more about the use of conditional statements in the next chapter of this tutorial. Logical Operators Logical operators are used to determine the logic between variables or values. Given that x=6 and y=3, the table below explains the logical operators: Operator Description Example && and (x < 10 && y > 1) is true
|| or (x==5 || y==5) is false
! not !(x==y) is true

Conditional Operator

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
Syntax

variablename=(condition)?value1:value2

Example

greeting=(visitor=="PRES")?"Dear President ":"Dear ";

If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value "Dear President " else it will be assigned "Dear".


Conditional statements in JavaScript are used to perform different actions based on different conditions.
Examples

If statement
How to write an if statement.

If...else statement
How to write an if...else statement.

If..else if...else statement
How to write an if..else if...else statement.

Random link
This example demonstrates a link, when you click on the link it will take you to W3Schools.com OR to RefsnesData.no. There is a 50% chance for each of them.
Conditional Statements

Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.

In JavaScript we have the following conditional statements:

* if statement - use this statement if you want to execute some code only if a specified condition is true
* if...else statement - use this statement if you want to execute some code if the condition is true and another code if the condition is false
* if...else if....else statement - use this statement if you want to select one of many blocks of code to be executed
* switch statement - use this statement if you want to select one of many blocks of code to be executed

If Statement

You should use the if statement if you want to execute some code only if a specified condition is true.
Syntax

if (condition)
{
code to be executed if condition is true
}

Note that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!
Example 1



Example 2



Note: When comparing variables you must always use two equals signs next to each other (==)!

Notice that there is no ..else.. in this syntax. You just tell the code to execute some code only if the specified condition is true.
If...else Statement

If you want to execute some code if a condition is true and another code if the condition is not true, use the if....else statement.
Syntax

if (condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}

Example



Conditional statements in JavaScript are used to perform different actions based on different conditions.
Examples

Switch statement
How to write a switch statement.
The JavaScript Switch Statement

You should use the switch statement if you want to select one of many blocks of code to be executed.
Syntax

switch(n)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is
different from case 1 and 2
}

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically.
Example



In JavaScript we can create three kinds of popup boxes: Alert box, Confirm box, and Prompt box.
Examples

Alert box

Alert box with line breaks

Confirm box

Prompt box
Alert Box

An alert box is often used if you want to make sure information comes through to the user.

When an alert box pops up, the user will have to click "OK" to proceed.

Syntax:

alert("sometext");


Confirm Box

A confirm box is often used if you want the user to verify or accept something.

When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.

If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false.

Syntax:

confirm("sometext");


Prompt Box

A prompt box is often used if you want the user to input a value before entering a page.

When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value.

If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.

Syntax:

prompt("sometext","defaultvalue");

A function is a reusable code-block that will be executed by an event, or when the function is called.
Examples

Function
How to call a function.

Function with arguments
How to pass a variable to a function, and use the variable in the function.

Function with arguments 2
How to pass variables to a function, and use these variables in the function.

Function that returns a value
How to let the function return a value.

A function with arguments, that returns a value
How to let the function find the product of two arguments and return the result.
JavaScript Functions

To keep the browser from executing a script when the page loads, you can put your script into a function.

A function contains code that will be executed by an event or by a call to that function.

You may call a function from anywhere within the page (or even from other pages if the function is embedded in an external .js file).

Functions can be defined both in the and in the section of a document. However, to assure that the function is read/loaded by the browser before it is called, it could be wise to put it in the section.
Example

If the line: alert("Hello world!!") in the example above had not been put within a function, it would have been executed as soon as the line was loaded. Now, the script is not executed before the user hits the button. We have added an onClick event to the button that will execute the function displaymessage() when the button is clicked.

You will learn more about JavaScript events in the JS Events chapter.
How to Define a Function

The syntax for creating a function is:

function functionname(var1,var2,...,varX)
{
some code
}

var1, var2, etc are variables or values passed into the function. The { and the } defines the start and end of the function.

Note: A function with no parameters must include the parentheses () after the function name:

function functionname()
{
some code
}

Note: Do not forget about the importance of capitals in JavaScript! The word function must be written in lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a function with the exact same capitals as in the function name.
The return Statement

The return statement is used to specify the value that is returned from the function.

So, functions that are going to return a value must use the return statement.
Example

The function below should return the product of two numbers (a and b):

function prod(a,b)
{
x=a*b;
return x;
}

When you call the function above, you must pass along two parameters:

product=prod(2,3);

The returned value from the prod() function is 6, and it will be stored in the variable called product.
The Lifetime of JavaScript Variables

When you declare a variable within a function, the variable can only be accessed within that function. When you exit the function, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different functions, because each is recognized only by the function in which it is declared.

If you declare a variable outside a function, all the functions on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

JavaScript Loops

Very often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal lines in a script we can use loops to perform a task like this.

In JavaScript there are two different kind of loops:

* for - loops through a block of code a specified number of times
* while - loops through a block of code while a specified condition is true

The for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax

for (var=startvalue;var<=endvalue;var=var+increment) { code to be executed } Example Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs. Note: The increment parameter could also be negative, and the <= could be any comparing statement.





Result

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

While loop
How to write a while loop. Use a while loop to run the same block of code while a specified condition is true.

Do while loop
How to write a do...while loop. Use a do...while loop to run the same block of code while a specified condition is true. This loop will always be executed at least once, even if the condition is false, because the statements are executed before the condition is tested.
The while loop

The while loop is used when you want the loop to execute and continue executing while the specified condition is true.

while (var<=endvalue) { code to be executed } Note: The <= could be any comparing statement. Example Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs.





Result

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

The do...while Loop

The do...while loop is a variant of the while loop. This loop will always execute a block of code ONCE, and then it will repeat the loop as long as the specified condition is true. This loop will always be executed at least once, even if the condition is false, because the code is executed before the condition is tested.

do
{
code to be executed
}
while (var<=endvalue); Example





Result

The number is 0
The number is 1
The number is 2

Continue

The continue command will break the current loop and continue with the next value.

Example







Result

The number is 0
The number is 1
The number is 2
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

JavaScript For...In Statement

The for...in statement is used to loop (iterate) through the elements of an array or through the properties of an object.

The code in the body of the for ... in loop is executed once for each element/property.

Syntax

for (variable in object)
{
code to be executed
}

The variable argument can be a named variable, an array element, or a property of an object.
Example

Using for...in to loop through an array:









Events

By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be detected by JavaScript.

Every element on a web page has certain events which can trigger JavaScript functions. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks on the button. We define the events in the HTML tags.

Examples of events:

* A mouse click
* A web page or an image loading
* Mousing over a hot spot on the web page
* Selecting an input box in an HTML form
* Submitting an HTML form
* A keystroke

Note: Events are normally used in combination with functions, and the function will not be executed before the event occurs!

For a complete reference of the events recognized by JavaScript, go to our complete Event reference.
onload and onUnload

The onload and onUnload events are triggered when the user enters or leaves the page.

The onload event is often used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.

Both the onload and onUnload events are also often used to deal with cookies that should be set when a user enters or leaves a page. For example, you could have a popup asking for the user's name upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you could have another popup saying something like: "Welcome John Doe!".
onFocus, onBlur and onChange

The onFocus, onBlur and onChange events are often used in combination with validation of form fields.

Below is an example of how to use the onChange event. The checkEmail() function will be called whenever the user changes the content of the field:




onSubmit

The onSubmit event is used to validate ALL form fields before submitting it.

Below is an example of how to use the onSubmit event. The checkForm() function will be called when the user clicks the submit button in the form. If the field values are not accepted, the submit should be cancelled. The function checkForm() returns either true or false. If it returns true the form will be submitted, otherwise the submit will be cancelled:

onMouseOver and onMouseOut

onMouseOver and onMouseOut are often used to create "animated" buttons.

Below is an example of an onMouseOver event. An alert box appears when an onMouseOver event is detected:





The try...catch statement allows you to test a block of code for errors.
Examples

The try...catch statement
How to write a try...catch statement.

The try...catch statement with a confirm box
Another example of how to write a try...catch statement.
JavaScript - Catching Errors

When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us there is a runtime error and asking "Do you wish to debug?". Error message like this may be useful for developers but not for users. When users see errors, they often leave the Web page.

This chapter will teach you how to trap and handle JavaScript error messages, so you don't lose your audience.

There are two ways of catching errors in a Web page:

* By using the try...catch statement (available in IE5+, Mozilla 1.0, and Netscape 6)
* By using the onerror event. This is the old standard solution to catch errors (available since Netscape 3)

Try...Catch Statement

The try...catch statement allows you to test a block of code for errors. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs.
Syntax

try
{
//Run some code here
}
catch(err)
{
//Handle errors here
}

Note that try...catch is written in lowercase letters. Using uppercase letters will generate a JavaScript error!
Example 1

The example below contains a script that is supposed to display the message "Welcome guest!" when you click on a button. However, there's a typo in the message() function. alert() is misspelled as adddlert(). A JavaScript error occurs:












To take more appropriate action when an error occurs, you can add a try...catch statement.

The example below contains the "Welcome guest!" example rewritten to use the try...catch statement. Since alert() is misspelled, a JavaScript error occurs. However, this time, the catch block catches the error and executes a custom code to handle it. The code displays a custom error message informing the user what happened:












Example 2

The next example uses a confirm box to display a custom message telling users they can click OK to continue viewing the page or click Cancel to go to the homepage. If the confirm method returns false, the user clicked Cancel, and the code redirects the user. If the confirm method returns true, the code does nothing:












The throw statement allows you to create an exception.
Examples

The throw statement
How to use the throw statement.
The Throw Statement

The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages.
Syntax

throw(exception)

The exception can be a string, integer, Boolean or an object.

Note that throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error!
Example 1

The example below determines the value of a variable called x. If the value of x is higher than 10 or lower than 0 we are going to throw an error. The error is then caught by the catch argument and the proper error message is displayed:












In JavaScript you can add special characters to a text string by using the backslash sign.
Insert Special Characters

The backslash (\) is used to insert apostrophes, new lines, quotes, and other special characters into a text string.

Look at the following JavaScript code:

var txt="We are the so-called "Vikings" from the north.";
document.write(txt);

In JavaScript, a string is started and stopped with either single or double quotes. This means that the string above will be chopped to: We are the so-called

To solve this problem, you must place a backslash (\) before each double quote in "Viking". This turns each double quote into a string literal:

var txt="We are the so-called \"Vikings\" from the north.";
document.write(txt);

JavaScript will now output the proper text string: We are the so-called "Vikings" from the north.

Here is another example:

document.write ("You \& I are singing!");

The example above will produce the following output:

You & I are singing!

The table below lists other special characters that can be added to a text string with the backslash sign:
Code Outputs
\' single quote
\" double quote
\& ampersand
\\ backslash
\n new line
\r carriage return
\t tab
\b backspace
\f form feed

JavaScript is Case Sensitive

A function named "myfunction" is not the same as "myFunction" and a variable named "myVar" is not the same as "myvar".

JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables, objects and functions.
White Space

JavaScript ignores extra spaces. You can add white space to your script to make it more readable. The following lines are equivalent:

name="Hege";
name = "Hege";


Break up a Code Line

You can break up a code line within a text string with a backslash. The example below will be displayed properly:

document.write("Hello \
World!");

However, you cannot break up a code line like this:

document.write \
("Hello World!");

JavaScript is an Object Oriented Programming (OOP) language.

An OOP language allows you to define your own objects and make your own variable types.
Object Oriented Programming

JavaScript is an Object Oriented Programming (OOP) language. An OOP language allows you to define your own objects and make your own variable types.

However, creating your own objects will be explained later, in the Advanced JavaScript section. We will start by looking at the built-in JavaScript objects, and how they are used. The next pages will explain each built-in JavaScript object in detail.

Note that an object is just a special kind of data. An object has properties and methods.
Properties

Properties are the values associated with an object.

In the following example we are using the length property of the String object to return the number of characters in a string:



The output of the code above will be:

12


Methods

Methods are the actions that can be performed on objects.

In the following example we are using the toUpperCase() method of the String object to display a text in uppercase letters:



The output of the code above will be:

HELLO WORLD!

The String object is used to manipulate a stored piece of text.
Examples

Return the length of a string
How to use the length property to find the length of a string.

Style strings
How to style strings.

The indexOf() method
How to use the indexOf() method to return the position of the first occurrence of a specified string value in a string.

The match() method
How to use the match() method to search for a specified string value within a string and return the string value if found

Replace characters in a string - replace()
How to use the replace() method to replace some characters with some other characters in a string.
Complete String Object Reference

For a complete reference of all the properties and methods that can be used with the String object, go to our complete String object reference.

The reference contains a brief description and examples of use for each property and method!
String object

The String object is used to manipulate a stored piece of text.

Examples of use:

The following example uses the length property of the String object to find the length of a string:

var txt="Hello world!";
document.write(txt.length);

The code above will result in the following output:

12

The following example uses the toUpperCase() method of the String object to convert a string to uppercase letters:

var txt="Hello world!";
document.write(txt.toUpperCase());

The code above will result in the following output:

HELLO WORLD!

The Date object is used to work with dates and times.
Examples

Return today's date and time
How to use the Date() method to get today's date.

getTime()
Use getTime() to calculate the years since 1970.

setFullYear()
How to use setFullYear() to set a specific date.

toUTCString()
How to use toUTCString() to convert today's date (according to UTC) to a string.

getDay()
Use getDay() and an array to write a weekday, and not just a number.

Display a clock
How to display a clock on your web page.
Complete Date Object Reference

For a complete reference of all the properties and methods that can be used with the Date object, go to our complete Date object reference.

The reference contains a brief description and examples of use for each property and method!
Create a Date Object

The Date object is used to work with dates and times.

The following code create a Date object called myDate:

var myDate=new Date()

Note: The Date object will automatically hold the current date and time as its initial value!
Set Dates

We can easily manipulate the date by using the methods available for the Date object.

In the example below we set a Date object to a specific date (14th January 2010):

var myDate=new Date();
myDate.setFullYear(2010,0,14);

And in the following example we set a Date object to be 5 days into the future:

var myDate=new Date();
myDate.setDate(myDate.getDate()+5);

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself!
Compare Two Dates

The Date object is also used to compare two dates.

The following example compares today's date with the 14th January 2010:

var myDate=new Date();
myDate.setFullYear(2010,0,14);

var today = new Date();

if (myDate>today)
{
alert("Today is before 14th January 2010");
}
else
{
alert("Today is after 14th January 2010");
}


The Array object is used to store multiple values in a single variable.
Examples

Create an array
Create an array, assign values to it, and write the values to the output.

For...In Statement
How to use a for...in statement to loop through the elements of an array.

Join two arrays - concat()
How to use the concat() method to join two arrays.

Put array elements into a string - join()
How to use the join() method to put all the elements of an array into a string.

Literal array - sort()
How to use the sort() method to sort a literal array.

Numeric array - sort()
How to use the sort() method to sort a numeric array.
Complete Array Object Reference

For a complete reference of all the properties and methods that can be used with the Array object, go to our complete Array object reference.

The reference contains a brief description and examples of use for each property and method!
Create an Array

The following code creates an Array object called myCars:

var myCars=new Array()

There are two ways of adding values to an array (you can add as many values as you need to define as many variables you require).

1:

var myCars=new Array();
mycars[0]="Saab";
mycars[1]="Volvo";
mycars[2]="BMW";

You could also pass an integer argument to control the array's size:

var myCars=new Array(3);
mycars[0]="Saab";
mycars[1]="Volvo";
mycars[2]="BMW";

2:

var myCars=new Array("Saab","Volvo","BMW");

Note: If you specify numbers or true/false values inside the array then the type of variables will be numeric or Boolean instead of string.
Access an Array

You can refer to a particular element in an array by referring to the name of the array and the index number. The index number starts at 0.

The following code line:

document.write(myCars[0]);

will result in the following output:

Saab


Modify Values in an Array

To modify a value in an existing array, just add a new value to the array with a specified index number:

myCars[0]="Opel";

Now, the following code line:

document.write(myCars[0]);

will result in the following output:

Opel


The Boolean object is used to convert a non-Boolean value to a Boolean value (true or false).
Examples

Check Boolean value
Check if a Boolean object is true or false.
Complete Boolean Object Reference

For a complete reference of all the properties and methods that can be used with the Boolean object, go to our complete Boolean object reference.

The reference contains a brief description and examples of use for each property and method!
Create a Boolean Object

The Boolean object represents two values: "true" or "false".

The following code creates a Boolean object called myBoolean:

var myBoolean=new Boolean();

Note: If the Boolean object has no initial value or if it is 0, -0, null, "", false, undefined, or NaN, the object is set to false. Otherwise it is true (even with the string "false")!

All the following lines of code create Boolean objects with an initial value of false:

var myBoolean=new Boolean();
var myBoolean=new Boolean(0);
var myBoolean=new Boolean(null);
var myBoolean=new Boolean("");
var myBoolean=new Boolean(false);
var myBoolean=new Boolean(NaN);

And all the following lines of code create Boolean objects with an initial value of true:

var myBoolean=new Boolean(true);
var myBoolean=new Boolean("true");
var myBoolean=new Boolean("false");
var myBoolean=new Boolean("Richard");

The Math object allows you to perform mathematical tasks.
Examples

round()
How to use round().

random()
How to use random() to return a random number between 0 and 1.

max()
How to use max() to return the number with the highest value of two specified numbers.

min()
How to use min() to return the number with the lowest value of two specified numbers.
Complete Math Object Reference

For a complete reference of all the properties and methods that can be used with the Math object, go to our complete Math object reference.

The reference contains a brief description and examples of use for each property and method!
Math Object

The Math object allows you to perform mathematical tasks.

The Math object includes several mathematical constants and methods.

Syntax for using properties/methods of Math:

var pi_value=Math.PI;
var sqrt_value=Math.sqrt(16);

Note: Math is not a constructor. All properties and methods of Math can be called by using Math as an object without creating it.
Mathematical Constants

JavaScript provides eight mathematical constants that can be accessed from the Math object. These are: E, PI, square root of 2, square root of 1/2, natural log of 2, natural log of 10, base-2 log of E, and base-10 log of E.

You may reference these constants from your JavaScript like this:

Math.E
Math.PI
Math.SQRT2
Math.SQRT1_2
Math.LN2
Math.LN10
Math.LOG2E
Math.LOG10E


Mathematical Methods

In addition to the mathematical constants that can be accessed from the Math object there are also several methods available.

The following example uses the round() method of the Math object to round a number to the nearest integer:

document.write(Math.round(4.7));

The code above will result in the following output:

5

The following example uses the random() method of the Math object to return a random number between 0 and 1:

document.write(Math.random());

The code above can result in the following output:

0.0639301019295192

The following example uses the floor() and random() methods of the Math object to return a random number between 0 and 10:

document.write(Math.floor(Math.random()*11));

The code above can result in the following output:

3

What is RegExp

RegExp, is short for regular expression.

When you search in a text, you can use a pattern to describe what you are searching for. RegExp IS this pattern.

A simple pattern can be a single character.

A more complicated pattern consists of more characters, and can be used for parsing, format checking, substitution and more.

You can specify where in the string to search, what type of characters to search for, and more.
Defining RegExp

The RegExp object is used to store the search pattern.

We define a RegExp object with the new keyword. The following code line defines a RegExp object called patt1 with the pattern "e":

var patt1=new RegExp("e");

When you use this RegExp object to search in a string, you will find the letter "e".
Methods of the RegExp Object

The RegExp Object has 3 methods: test(), exec(), and compile().
test()

The test() method searches a string for a specified value. Returns true or false
Example:

var patt1=new RegExp("e");

document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

true

Try it yourself
exec()

The exec() method searches a string for a specified value. Returns the text of the found value. If no match is found, it returns null
Example 1:

var patt1=new RegExp("e");

document.write(patt1.exec("The best things in life are free"));

Since there is an "e" in the string, the output of the code above will be:

e

Try it yourself
Example 2:

You can add a second parameter to the RegExp object, to specify your search. For example; if you want to find all occurrences of a character, you can use the "g" parameter ("global").

For a complete list of how to modify your search, visit our complete RegExp object reference.

When using the "g" parameter, the exec() method works like this:

* Finds the first occurence of "e", and stores its position
* If you run exec() again, it starts at the stored position, and finds the next occurence of "e", and stores its position

var patt1=new RegExp("e","g");
do
{
result=patt1.exec("The best things in life are free");
document.write(result);
}
while (result!=null)

Since there is six "e" letters in the string, the output of the code above will be:

eeeeeenull

Try it yourself
compile()

The compile() method is used to change the RegExp.

compile() can change both the search pattern, and add or remove the second parameter.
Example:

var patt1=new RegExp("e");

document.write(patt1.test("The best things in life are free"));

patt1.compile("d");

document.write(patt1.test("The best things in life are free"));

Since there is an "e" in the string, but not a "d", the output of the code above will be:

truefalse

Try it yourself
Complete RegExp Object Reference

For a complete reference of all the properties and methods that can be used with the RegExp object, go to our complete RegExp object reference.

The reference contains a brief description and examples of use for each property and method including the string object

More JavaScript Objects

Follow the links to learn more about the objects and their collections, properties, methods and events.
Object Description
Window The top level object in the JavaScript hierarchy. The Window object represents a browser window. A Window object is created automatically with every instance of a or tag
Navigator Contains information about the client's browser
Screen Contains information about the client's display screen
History Contains the visited URLs in the browser window
Location Contains information about the current URL

The HTML DOM

The HTML DOM is a W3C standard and it is an abbreviation for the Document Object Model for HTML.

The HTML DOM defines a standard set of objects for HTML, and a standard way to access and manipulate HTML documents.

All HTML elements, along with their containing text and attributes, can be accessed through the DOM. The contents can be modified or deleted, and new elements can be created.

The HTML DOM is platform and language independent. It can be used by any programming language like Java, JavaScript, and VBScript.

Follow the links below to learn more about how to access and manipulate each DOM object with JavaScript:
Object Description
Document Represents the entire HTML document and can be used to access all elements in a page
Anchor Represents an element
Area Represents an element inside an image-map
Base Represents a element
Body Represents the element
Button Represents a