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JavaScript : Variables
A variable's purpose is to store information so that it can be used later.
It is ideal to name a variable something that is logical, so that you'll
remember what you are using it for. For example, if you were writing a program
to calculate the speed, it could be confusing if you called your variables
inputOne, inputTwo, result because you may forget which one is the distance,
which one is the time, and which one is the speed. A more logical approach
would be to name them just that: distance, time, speed.
Naming Conventions: Basic Rules
- Variable names are case sensitive (myVal and MyVal are two different variables
in Javascript)
- They must start with a letter or underscore ("_")
- Subsequent characters can also be digits (0-9) or letters (A-Z and/or a-z).
- We cannot use reserved word as a variable name
- Variable name cannot contain space character
How to Create Variable
To declare a new variable called age using var keyword
Example:
var age ;
Intializing the Variable
var age=30 ;
var name="Abhishek" ;
If I declare a variable in one statement and later want to assign a value to it,the
sequence of statement is :
var age ;
age=30 ;
Datatype In JavaScript
| Type | Example | Description |
| String | "Abhishek" | A series of characters inside quote marks |
| Number | 7.9 | Any number not inside quote marks |
| Boolean | true | A logical true or false |
| NULL | null | Completely devoid of any value |
| Object | arrays | A software "thing" that is defined by its properties and method |
| Function | sqr | A function defintion |
Example
<html>
<head>
<title>Variable Example</title>
</head>
<body>
<script type="text/javascript">
var FirstName;
FirstName="Abhishek";
document.write(FirstName);
document.write("<br />");
var LastName="Sinha";
document.write(FirstName+" "+LastName);
</script>
<p> I am from B.H.U</p>
</body>
</html>
Output
Abhishek
Abhishek Sinha
I am from B.H.U
Scope of Variable
Global Variable
When you declare a variable by assignment outside of a function, it is called a global variable, because it is available everywhere in the current document
Local Variable
When you declare a variable within a function, it is called a local variable, because it is available only within the function.
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