PHP Developers

Wednesday, August 29, 2012

JavaScript Objects Introduction

JavaScript is an Object Based Programming language.

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

Object Based Programming

JavaScript is an Object Based Programming language, and 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:

<script>
var txt="Hello World!";
document.write(txt.length);
</script>

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:

<script>
var str="Hello world!";
document.write(str.toUpperCase());
</script>

The output of the code above will be:

HELLO WORLD!

Tuesday, August 28, 2012

JavaScript Guidelines

Some other important things to know when scripting with JavaScript.

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:

var name="Hege";
var 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 Special Characters

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.

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
\\	backslash
\n	new line
\r	carriage return
\t	tab
\b	backspace
\f	form feed

JavaScript Throw Statement

The throw statement allows you to create an exception.

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

The example below determines the value of a variable called x. If the value of x is higher than 10, lower than 5, or not a number, we are going to throw an error. The error is then caught by the catch argument and the proper error message is displayed:

Example

<!DOCTYPE html>
<html>
<body>
<script>
var x=prompt("Enter a number between 5 and 10:","");
try
  {
  if(x>10)
    {
    throw "Err1";
    }
  else if(x<5)
    {
    throw "Err2";
    }
  else if(isNaN(x))
    {
    throw "Err3";
    }
  }
catch(err)
  {
  if(err=="Err1")
    {
    document.write("Error! The value is too high.");
    }
  if(err=="Err2")
    {
    document.write("Error! The value is too low.");
    }
  if(err=="Err3")
    {
    document.write("Error! The value is not a number.");
    }
  }
</script>
</body>
</html>

Try it yourself »