Understanding JavaScript part - 2 (Introdution to variables and pop-up boxes)

Hello,
It's been long time since I wrote my last article on this series. You may like to read first part of this series named Understanding-javasript-part-1-getting-started. Let's continue on with part 2. Today you will learn how to declare/create variables, how to use them, what are their types, and what are pop-up boxes.

*Introduction to Variables:

What are variables? Variables are nothing but a construct in which we store values. Variables are important in Javascript. You should get familiar with this term. Don't worry,by the end of this topic you will be more familiar with variables.

Creating Variables:

To create variable there is syntax you should be familiar with:

Syntax:

var your_variable_name = "string" or (number);

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Notes,
Example

var (then) my_first_variable = 'this is var';

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That's it! You just created your first variable.So lets checked if you do it right or so,
To check what is variable use 'alert' command to check this out.

alert(my_first_variable);

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You will get whatever contain you defined variable in output screen.In this case you will get 'this is var'

*Pop-up boxes

Before we go further lets take a look at what are pop-up boxes,

Like alert which you know very well now and which use to show alert messages to user we have two more commands available which works very much similar to alert.

1. Prompt

In prompt you can ask questions to user and without answering them he could not go further in you web site. This prompt boxes are useful to get user's name or city name etc.

Example

prompt('Please enter your name','xyz')

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Here in above code,first string, i.e. in between quotes ('') will ask a user his name and second string will give some default value to it so that user can change it or leave it as it is. However second one is optional.

The output of above will be,

2. Confirm

Confirm command can use to ask user whether he want to continue on or not. Let's take an example,

confirm('This will continue to next page,'+'\n'+' Do you want to continue??');

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Then user will get two options ('OK','cancel') then you can use Javascript to execute bit of code if user clicks on 'OK' or execute another bit of code if he clicks 'cancel' etc.
Here how it will look,
This above three commands commonly known as 'pop-up' boxes. Pop-up boxes normally use in demonstration purpose only. You should be careful while using this boxes on your remote website at a time this boxes may become frustrating to your users and they might leave your website,and that what you don't want at any cost. right? :-)

*Continue on with variables:

var myElement = 'This is My variable';

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As you know variable can have stings or numbers in it. Like other programming languages,there is one more advantage in Javascript that there is no float, int like keywords to define strings and numbers separately. In Javascript we only use 'var' keyword to define all this things.

*Types of variables:

1. Global

2. Local

Global Variables:
The defined Global variables are available to use anywhere in Javascript. The scope of global variables is far more larger than that of local variables. Declaring global variables are easy,

<script type="text/Javascript">
                      	Var my_Global_Variable = "This is my global variable which i can use anywhere in Javascript"
                      </script> 

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Local Variables:
Local variables are those who can not used anywhere in Javascript,they have some limitation. Local variables are declared in function. Their scope is small but they are far more important than global ones. You should always avoid to make global variables.

<script type="text/Javascript">
                      	Function myfuncion() {
                      		Var my_local_Variable = "this variable is only used in this particular function"
                      	}
                      <script>

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In simple words,
Variables which are outside of functions are global variables and those who are inside functions are local variables.

<script type="text/Javascript">
                      
                      Var global_variable = "This is global variable";
                      
                      Function myfunction () {
                      	Var myElement= "This is local variable";
                      
                      }
                      </script>

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*Something you should keep remember:

*Summary:

By the end of this article you have got basic knowledge of declaring and creating variables. You also knew how to create pop-up boxes on your own,how they works and when to use them. So try practicing them and get grip of this topic.Next up,statements in Javascript.

Quiz,

Lets quickly take a quiz on variables and check if oyu can solve this question.The answers will be at end of this article.I will suggest you not to check answers without solving it first.

1.The variable name var _myVariable is valid.
A) True
B) False.

2.The variable name can start with a [i]'$' [/i]sign?
A) False
B) True

3.Variables are of two types Local variables and ______ ??
A) Global
B) Nobal

4.What is the purpose of prompt command??
A) To get a name from user and display it in webpage
B) Ask user whether s/he want to continue on further.

5.The syntax of variable is,
A)int your_variable_name = "string" or (number)
B)var your_variable_name = "string" or (number);

Answers:
1: B
2: B
3: A
4: A
5: B

Hope everybody have got full marks. If not then please go on and read this article again and specially grab variables concept perfectly. See you at next part.