The Bitwise Operators

There are following bitwise operators supported by JavaScript language
Assume variable A holds 2 and variable B holds 3 then:

Operator	Description	Example
&	Called Bitwise AND operator. It performs a Boolean AND operation on each bit of its integer arguments.	(A & B) is 2 .
|	Called Bitwise OR Operator. It performs a Boolean OR operation on each bit of its integer arguments.	(A | B) is 3.
^	Called Bitwise XOR Operator. It performs a Boolean exclusive OR operation on each bit of its integer arguments. Exclusive OR means that either operand one is true or operand two is true, but not both.	(A ^ B) is 1.
~	Called Bitwise NOT Operator. It is a is a unary operator and operates by reversing all bits in the operand.	(~B) is -4 .
<<	Called Bitwise Shift Left Operator. It moves all bits in its first operand to the left by the number of places specified in the second operand. New bits are filled with zeros. Shifting a value left by one position is equivalent to multiplying by 2, shifting two positions is equivalent to multiplying by 4, etc.	(A << 1) is 4.
>>	Called Bitwise Shift Right with Sign Operator. It moves all bits in its first operand to the right by the number of places specified in the second operand. The bits filled in on the left depend on the sign bit of the original operand, in order to preserve the sign of the result. If the first operand is positive, the result has zeros placed in the high bits; if the first operand is negative, the result has ones placed in the high bits. Shifting a value right one place is equivalent to dividing by 2 (discarding the remainder), shifting right two places is equivalent to integer division by 4, and so on.	(A >> 1) is 1.
>>>	Called Bitwise Shift Right with Zero Operator. This operator is just like the >> operator, except that the bits shifted in on the left are always zero,	(A >>> 1) is 1.

The Comparison Operators

here are following comparison operators supported by JavaScript language
Assume variable A holds 10 and variable B holds 20 then:

Operator	Description	Example
==	Checks if the value of two operands are equal or not, if yes then condition becomes true.	(A == B) is not true.
!=	Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

What is an operator?

Simple answer can be given using expression 4 + 5 is equal to 9. Here 4 and 5 are called operands and + is called operator. JavaScript language supports following type of operators.

• Arithmetic Operators
• Comparision Operators
• Logical (or Relational) Operators
• Assignment Operators
• Conditional (or ternary) Operators

Lets have a look on all operators one by one.

The Arithmatic Operators:

There are following arithmatic operators supported by JavaScript language:
Assume variable A holds 10 and variable B holds 20 then:

Operator	Description	Example
+	Adds two operands	A + B will give 30
-	Subtracts second operand from the first	A - B will give -10
*	Multiply both operands	A * B will give 200
/	Divide numerator by denumerator	B / A will give 2
%	Modulus Operator and remainder of after an integer division	B % A will give 0
++	Increment operator, increases integer value by one	A++ will give 11
--	Decrement operator, decreases integer value by one	A-- will give 9

Note: Addition operator (+) works for Numeric as well as Strings. e.g. "a" + 10 will give "a10".

JavaScript Reserved Words

The following are reserved words in JavaScript. They cannot be used as JavaScript variables, functions, methods, loop labels, or any object names.

abstract boolean break byte case catch char class const continue debugger default delete do double

else enum export extends false final finally float for function goto if implements import in

instanceof int interface long native new null package private protected public return short static super

switch synchronized this throw throws transient true try typeof var void volatile while with

JavaScript Variable Scope

The scope of a variable is the region of your program in which it is defined. JavaScript variable will have only two scopes.

• Global Variables: A global variable has global scope which means it is defined everywhere in your JavaScript code.
• Local Variables: A local variable will be visible only within a function where it is defined. Function parameters are always local to that function.

Within the body of a function, a local variable takes precedence over a global variable with the same name. If you declare a local variable or function parameter with the same name as a global variable, you effectively hide the global variable. Following example explains it:

<script type="text/javascript"> <!-- var myVar = "global"; // Declare a global variable function checkscope( ) { var myVar = "local"; // Declare a local variable document.write(myVar); } //--> </script>

This produces the following result:

local

JavaScript DataTypes

One of the most fundamental characteristics of a programming language is the set of data types it supports. These are the type of values that can be represented and manipulated in a programming language.
JavaScript allows you to work with three primitive data types:

• Numbers eg. 123, 120.50 etc.
• Strings of text e.g. "This text string" etc.
• Boolean e.g. true or false.

JavaScript also defines two trivial data types, null and undefined, each of which defines only a single value.

JavaScript in External File

As you begin to work more extensively with JavaScript, you will likely find that there are cases where you are reusing identical JavaScript code on multiple pages of a site.

You are not restricted to be maintaining identical code in multiple HTML files. The script tag provides a mechanism to allow you to store JavaScript in an external file and then include it into your HTML files.


Here is an example to show how you can include an external JavaScript file in your HTML code using script tag and its src attribute:

<html>
<head>
<script type="text/javascript" src="filename.js" ></script>
</head>
<body>
.......
</body>
</html>